
[Federal Register: July 21, 2008 (Volume 73, Number 140)]
[Rules and Regulations]
[Page 42443-42504]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr21jy08-12]


[[Page 42443]]

-----------------------------------------------------------------------

Part III





Department of Transportation





-----------------------------------------------------------------------



Federal Aviation Administration



14 CFR Parts 25, 26, 121 et al.



Reduction of Fuel Tank Flammability in Transport Category Airplanes;
Final Rule


[[Page 42444]]


-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 25, 26, 121, 125, and 129

[Docket No. FAA-2005-22997; Amendment Nos. 25-125, 26-2, 121-340, 125-
55, and 129-46]
RIN 2120-AI23


Reduction of Fuel Tank Flammability in Transport Category
Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule, request for comments.

-----------------------------------------------------------------------

SUMMARY: This final rule amends FAA regulations that require operators
and manufacturers of transport category airplanes to take steps that,
in combination with other required actions, should greatly reduce the
chances of a catastrophic fuel tank explosion. The final rule does not
direct the adoption of specific inerting technology either by
manufacturers or operators, but establishes a performance-based set of
requirements that set acceptable flammability exposure values in tanks
most prone to explosion or require the installation of an ignition
mitigation means in an affected fuel tank. Technology now provides a
variety of commercially feasible methods to accomplish these vital
safety objectives.

DATES: These amendments become September 19, 2008. Send your comments
by January 20, 2009. The incorporation by reference of the document
listed in the rule is approved by the Director of the Federal Register
as of September 19, 2008.

FOR FURTHER INFORMATION CONTACT: If you have technical questions about
this action, contact Michael E. Dostert, FAA, Propulsion/Mechanical
Systems Branch, ANM-112, Transport Airplane Directorate, Aircraft
Certification Service, 1601 Lind Avenue, SW., Renton, Washington 98057-
3356; telephone (425) 227-2132, facsimile (425) 227-1320; e-mail:
mike.dostert@faa.gov. Direct any legal questions to Doug Anderson, ANM-
7, FAA, Office of Regional Counsel, 1601 Lind Avenue, SW, Renton, WA
98057-3356; telephone (425) 227-2166; facsimile (425) 227-1007, e-mail
Douglas.Anderson@faa.gov.

SUPPLEMENTARY INFORMATION: Later in this preamble under the ADDITIONAL
INFORMATION section, we discuss how you can comment on a certain
portion of this final rule and how we will handle your comments.
Included in this discussion is related information about the docket,
privacy, and the handling of proprietary or confidential business
information. We also discuss how you can get a copy of this final rule
and related rulemaking documents.

Authority for Rulemaking

    The FAA's authority to issue rules regarding aviation safety is
found in Title 49 of the United States Code. Subtitle I, Section 106
describes the authority of the FAA Administrator. Subtitle VII,
Aviation Programs, describes in more detail the scope of the agency's
authority.
    This rulemaking is promulgated under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701, ``General
requirements.'' Under that section, the FAA is charged with promoting
safe flight of civil aircraft in air commerce by prescribing minimum
standards required in the interest of safety for the design and
performance of aircraft; regulations and minimum standards in the
interest of aviation safety for inspecting, servicing, and overhauling
aircraft; and regulations for other practices, methods, and procedures
the Administrator finds necessary for safety in air commerce. This
regulation is within the scope of that authority because it prescribes
     New safety standards for the design of transport category
airplanes, and
     New requirements necessary for safety for the design,
production, operation and maintenance of those airplanes, and for other
practices, methods, and procedures related to those airplanes.

Table of Contents

I. Executive Summary
    A. Statement of the Problem
    B. Reducing the Chance of Ignition
    C. Reducing the Likelihood of an Explosion After Ignition
II. Background
    A. Summary of the NPRM
    B. Related Activities
    C. Differences Between the NPRM and the Final Rule
III. Discussion of the Final Rule
    A. Summary of Comments
    B. Necessity of Rule
    1. Estimates/Conclusions Supporting Need for Rule
    2. Additional Research Needed
    3. Consistent Safety Level With Other Systems
    4. Human Errors
    5. Explosion Risk Analysis
    6. Special Certification Review Process vs. Rulemaking
    7. Flammability Reduction Means (FRM) Effectiveness
    C. Applicability
    1. Airplanes With Fewer Than 30 Seats
    2. Part 91 and 125 Operators
    3. All-Cargo Airplanes
    4. Specific Airplane Models
    5. Wing Tanks
    6. Auxiliary Fuel Tanks
    7. Existing Horizontal Stabilizer Fuel Tanks
    8. Foreign Persons/Air Carriers Operating U.S. Registered
Airplanes
    9. Airplanes Operated Under Sec.  121.153
    10. International Aspects of Production Requirements
    D. Requirements for Manufacturers and Holders of Type
Certificates, Supplemental Type Certificates and Field Approvals
    1. General Comments About Design Approval Holder (DAH)
Requirements
    2. Flammability Exposure Level Requirements for New Airplane
Designs
    3. Flammability Exposure Requirements for Current Airplane
Designs
    4. Continued Airworthiness and Safety Improvements
    E. Flammability Exposure Requirements for Airplane Operators
    1. General Comments About Applicability to Existing Airplanes
    2. Authority to Operate With an Inoperative FRM, IMM or FIMM
    3. Availability of Spare Parts
    4. Requirement That Center Fuel Tank be Inert Before First
Flight of the Day
    F. Appendix M--FRM Specifications
    1. Fleet Average Flammability Exposure Levels
    2. Inclusion of Ground and Takeoff/Climb Phases of Flight
    3. Clarification of Sea Level Ground Ambient Temperature
    4. Deletion of Proposed Paragraph M25.2 (Showing Compliance)
    5. Deletion of ``Fuel Type'' From List of Requirements in
Proposed Paragraph M25.2(b)
    6. Latent Failures
    7. Identification of Airworthiness Limitations
    8. Catastrophic Failure Modes
    9. Reliability Reporting
    G. Appendix N--Fuel Tank Flammability Exposure and Reliability
Analysis
    1. General
    2. Definitions
    3. Input Parameters
    4. Verification of ``Flash Point Temperature''
    H. Critical Design Configuration Control Limitations (CDCCL)
    1. Remove Requirement
    2. Clarification on Responsibility for Later Modifications
    3. Limit CDCCL's to Fuel Tanks That Require FRM or IMM
    4. STC Holders May Not Have Data to Comply
    I. Methods of Mitigating the Likelihood of a Fuel Tank Explosion
    1. Alternatives to Inerting
    2. Inerting Systems Could Create Ignition Sources
    3. Instruments to Monitor Inerting Systems
    4. Risk of Nitrogen Asphyxiation
    5. Warning Placards
    6. Definition of ``Inert''
    7. Use of Carbon Dioxide
    8. Environmental Impact of FRM
    9. Current FRMs Fail to Meet Requirements

[[Page 42445]]

    10. FRM Based on Immature Technology
    J. Compliance Dates
    1. Part 26 Design Approval Holder Compliance Dates
    2. Operator Fleet Retrofit Compliance Dates
    K. Cost/Benefit Analysis
    1. Security Benefits
    2. Likelihood of Future Explosions in Flight
    3. Costs to Society of Future Accidents
    4. Value of a Prevented Fatality
    5. Cost Savings if Transient Suppression Units (TSUs) are not
Required
    6. Corrections About Boeing Statements
    7. 757 Size Category
    8. Number of Future Older In-Service Airplanes Overestimated
    9. Revisions to the FRM Kit Costs
    10. Revisions to the Labor Time to Retrofit FRM Components
    11. Retrofitting Costs per Airplane
    12. Percentage of Retrofits Completed During a Heavy Check
    13. Number of Additional Days of Out-of-Service Time to Complete
a Retrofit
    14. Economic Losses From an Out-of-Service Day
    15. Updated FRM Weight Data
    16. Updated Fuel Consumption Data
    17. Updated Fuel Cost Data
    18. Cost of Inspections
    19. Inspection and Maintenance Labor Hours
    20. Daily Check
    21. Spare Parts Costs
    22. Air Separation Model (ASM) Replacement
    L. Miscellaneous
    1. Harmonization
    2. Part 25 Safety Targets
IV. Regulatory Notices and Analyses
V. The Amendment

I. Executive Summary

A. Statement of the Problem

    Fuel tank explosions have been a constant threat with serious
aviation safety implications for many years. Since 1960, 18 airplanes
have been damaged or destroyed as the result of a fuel tank explosion.
Two of the more recent explosions--one involving a Boeing 747 (Trans
World Airways (TWA) Flight 800) off Long Island, New York in 1996 and
the other, a Boeing 727 terrorist-initiated explosion (Avianca Flight
203) in Bogot[aacute], Columbia in 1989 \1\--occurred during flight and
led to catastrophic losses (including the deaths of 337 individuals).
Two other recent explosions on airplanes operated by Philippine
Airlines and Thai Airlines occurred on the ground (resulting in nine
fatalities).\2\ While the accident investigations of the TWA,
Philippine Airlines and Thai Airlines accidents failed to identify the
ignition source that caused the explosion, the investigations found
several similarities. In each instance:
---------------------------------------------------------------------------

    \1\ Although it was determined that a terrorist's bomb had
caused the explosion of the center tank in the Bogot[aacute]
accident, the NTSB determined the ``bomb explosion did not
compromise the structural integrity of the airplane; however, the
explosion punctured the [center wing tank] and ignited the fuel-air
vapors in the ullage, resulting in destruction of the airplane.''
    \2\ Philippine Airlines Boeing 737 accidnet in Manila in 1990,
and a Thai Airlines Boeing 737 accident in Bangkok in 2001.
---------------------------------------------------------------------------

    1. The weather was warm, with an outside air temperature over 80
[deg]F;
    2. The explosion occurred on the ground or soon after takeoff; and
    3. The explosion involved empty or nearly empty tanks that
contained residual fuel from the previous fueling.
    Additionally, investigators were able to conclude that the center
wing fuel tank in all three airplanes contained flammable vapors in the
ullage (that portion of the fuel tank not occupied by liquid fuel) when
the fuel tanks exploded. This was also the case with the Avianca
airplane.
    A system designed to reduce the likelihood of a fuel tank fire, or
mitigate the effects of a fire should one occur, would have prevented
these four fuel tank explosions.
    A statistical evaluation of these accidents has led the FAA to
project that, unless remedial measures are taken, four more United
States (U.S.) registered transport category airplanes will likely be
destroyed by a fuel tank explosion in the next 35 years. Although we
cannot forecast precisely when these accidents will occur, computer
modeling that has been an accurate predictor in the past indicates
these events are virtually certain to occur. We believe at least three
of these explosions are preventable by the adoption of a comprehensive
safety regime to reduce both the incidence of ignition sources
developing and the likelihood of the fuel tank containing flammable
fuel vapors.

B. Reducing the Chance of Ignition

    To address the first part of this comprehensive safety regime, we
have taken several steps to reduce the chances of ignition. Since 1996,
we have imposed numerous airworthiness requirements (including
airworthiness directives or ``ADs'') directed at the elimination of
fuel tank ignition sources. Special Federal Aviation Regulation No. 88
of 14 Code of Federal Regulations (CFR) part 21 (SFAR 88; 66 FR 23086,
May 7, 2001) requires the detection and correction of potential system
failures that can cause ignition. Although these measures should
prevent some of the four forecast explosions, our review of the current
transport category airplane designs of all major manufacturers has
shown that unanticipated failures and maintenance errors will continue
to generate unexpected ignition sources. Since manufacturers completed
their SFAR 88 ignition prevention reviews, we have had reports of
potential ignition sources (including unsafe conditions) that were not
identified in the SFAR 88 reviews. For example:
     We issued AD 2006-06-14 to require the inspection of fuel
quantity indicating probes within the fuel tanks of Airbus A320
airplanes to prevent an ignition source due to sparks that could be
created following a lightning strike. This failure mode was not
identified as a possible ignition source in the SFAR 88 analysis
presented to the FAA.
     We issued AD 2006-12-02 following a report of an
improperly installed screw inside the fuel pump housings of A320
airplanes that could loosen and fall into the pump's electrical
windings. This could create a spark and ignite fuel vapors in the pump.
The ignited vapors could then exit the fuel pump housing, enter the
fuel tank through the hole created when the screw fell out of the
housing, and cause a fuel tank explosion. This failure mode was not
identified as a possible ignition source in the SFAR 88 analysis
presented to the FAA.
     We received an in-service report on a Boeing 777 that was
operated for over 30 days with an open vent hole between the center
wing fuel tank and the wheel well of the airplane. During maintenance,
a vent hole cover used to facilitate venting of the tank was
inadvertently left off. This was not discovered until a flight occurred
where the tank was fueled to a level where the fuel spilled from the
tank into the wheel well during pitching up of the airplane for
takeoff. Since the airplane brakes routinely exceed temperatures that
could ignite fuel vapors and the wheels are retracted into the wheel
well, the open vent port could have allowed ignition of fuel vapors in
the center tank and a fuel tank explosion. This type of maintenance
error was also not identified as providing a possible ignition source
during the SFAR 88 safety reviews.
     On May 5, 2006, an explosion occurred in the wing fuel
tank of a Boeing 727 in Bangalore, India, while the airplane was on the
ground. This event occurred after a modification to include special
Teflon sleeving and recurring inspections had been implemented to
prevent possible arcing of the fuel pump wires to metallic conduits
located in the fuel tank. Initial information indicates that the
identified

[[Page 42446]]

AD action was inadequate to prevent the formation of an ignition source
in the fuel tank and that the change intended to improve safety caused
premature wear of the sleeving and an unsafe condition. Premature wear
of Teflon sleeving on the Boeing 737 has also been reported, resulting
in AD action to modify the design and replace the existing sleeving.
This failure mode was not identified as a possible ignition source in
the SFAR 88 analysis presented to the FAA.
     We also received a report that during a recent
certification program test, an ignition source developed in the fuel
pumps causing pump failure. These pumps had been designed to meet the
most stringent requirements of SFAR 88 and Amendment 25-102 to 14 CFR
25.981 (issued concurrently with SFAR 88), yet the pump failed in a
manner that allowed a capacitor to arc to the pump enclosure and create
an ignition source. The applicant has since conducted a design review
that has resulted in numerous modifications to the pump's design.
     Following the TWA 800 accident, the risk of uncontrolled
fire adjacent to the fuel tanks causing a fuel tank explosion was
identified as an unsafe condition. In 2006, we issued a MD-80 AD (AD
2006-15-15) to prevent worn insulation on wires from arcing at the
auxiliary hydraulic pump, which could result in a fire in the wheel
well of the airplane. The AD required inspections to validate the pump
wire integrity as well as incorporating sleeving on portions of the
wires. In April 2008, we received reports of improper means of
compliance being used regarding the requirements of AD 2006-15-15.
Human error in completing the procedures required by the AD resulted in
airplanes being operated without the needed safety improvements.
    Based on the above examples, we have concluded that we are unlikely
to identify and eradicate all possible sources of ignition.

C. Reducing the Likelihood of an Explosion After Ignition

    To ensure safety, therefore, we must also focus on the environment
that permits combustion to occur in the first place. Many transport
category airplanes are designed with heated center wing tanks in which
the fuel vapors are flammable for significant portions of their
operating time. This final rule addresses the risk of a fuel tank
explosion by reducing the likelihood that fuel tank vapors will explode
when an ignition source is introduced into the tank.
    Technology now exists that can prevent ignition of flammable fuel
vapors by reducing their oxygen concentration below the level that will
support combustion. By making the vapors ``inert,'' we can
significantly reduce the likelihood of an explosion when a fire source
is introduced to the fuel tank. FAA-developed prototype onboard fuel
tank inerting systems have been successfully flight tested on Airbus
A320 and Boeing 747 and 737 airplanes. We have also approved inerting
systems for the Boeing 747 and 737 airplanes, and two airplanes of each
model type have performed as expected during airline in-service
evaluations. Boeing plans to install these systems on all new
production airplanes.
    Given that ignition sources will develop, the chances of a fuel
tank explosion naturally correlate with the exposure of the tank to
flammable vapors. The requirements in this final rule mitigate the
effects of such flammability exposure and limit it to acceptable levels
by mandating the installation of either a Flammability Reduction Means
(FRM) or an Ignition Mitigation Means (IMM).\3\ In either case, the
technology has to adhere to performance and reliability standards that
are set by us and contained in Appendices M and N to Title 14 Code of
Federal Regulations (CFR) part 25.
---------------------------------------------------------------------------

    \3\ FRM consist of systems or features installed to reduce or
control fuel tank flammability to acceptable levels. IMM is based
upon mitigating the effects of a fuel vapor ignition in a fuel tank
so that an explosion does not occur. Polyurethane foam installed in
a fuel tank is one form of an IMM. See AC 25.981-2 for additional
information.
---------------------------------------------------------------------------

    This final rule amends the existing airworthiness standards
contained in 14 CFR 25.981 to require all future type certificate (TC)
applicants for transport category airplanes to reduce fuel tank
flammability exposure to acceptable levels. It also amends 14 CFR part
26 ``Continued Airworthiness and Safety Improvements'' \4\ to require
TC holders to develop FRM or IMM for many large turbine-powered
transport category airplanes with high-risk fuel tanks. Finally, it
amends 14 CFR parts 121, 125 and 129 to require operators of these
airplanes to incorporate the approved FRM or IMM into the fleet and to
keep them operational. We estimate that approximately 2,700 existing
Airbus and Boeing airplanes operating in the United States as well as
about 2,300 newly manufactured airplanes that enter U.S. airline
passenger service will be affected. Fuel tank system designs in several
pending type-certification applications, including the Boeing 787 \5\
and Airbus A350, also have to meet these requirements.
---------------------------------------------------------------------------

    \4\ Part 26 was added to the Code of Federal Regulations to
include all requirements for Continued Operational Safety. See
Docket number FAA-2004-18379 for more information on this subject.
    \5\ This airplane model already includes a FRM in its design
that the applicant intends to show will meet today's final rule, so
no additional modifications will be required.
---------------------------------------------------------------------------

    We acknowledge that these requirements are costly and have adopted
these steps only after spending several years researching the most
cost-effective ways to prevent fuel tank explosions in cooperation with
engineers and other experts from the affected industry. Those efforts
have resulted in the development of fuel-inerting technology that is
vastly cheaper than originally thought.
    In contrast, the loss of a single, fully loaded large passenger
airplane in flight, such as a Boeing 747 or Airbus A380, would result
in death and destruction causing societal loss of at least $1.2 billion
(based on costs of prior calamities). We estimate that compliance with
this new rule will prevent between one and two accidents of some type
(for analytical purposes we assume the accidents would involve
``average'' airplanes with ``average'' passenger loads) over 35
years.\6\ In addition to the direct costs of such an accident, we now
recognize that, in the post-9/11 aviation environment, the public could
initially assume that an in-flight fuel tank explosion is the result of
terrorist actions. This could cause a substantial immediate disruption
of flights, similar to what occurred in Britain on August 10, 2006, due
to the discovery of a terrorist plot.\7\ This could have an immediate
and substantial adverse economic effect on the aviation industry as a
whole.
---------------------------------------------------------------------------

    \6\ Although Boeing has committed to installing compliant FRM in
all future production airplanes, regardless of this rule, operators
could deactivate the systems unless this rulemaking is adopted. The
final regulatory evaluation includes the costs and benefits of these
actions for newly produced Boeing and Airbus airplanes.
    \7\ Flight schedules in Britain were significantly disrupted due
to flight cancellation of all flights into Heathrow Airport and 30
percent of all short-haul flights out of Heathrow Airport for one
day (according to Secretary of State for Transport Douglas
Alexander). The day after the event, the crowds and lines that log-
jammed British airports the day before were largely gone, he said.
British Airways stated that it cancelled 1,280 flights between
August 10-17 due to the discovery of the terror plot and subsequent
security measures. EasyJet said it was forced to cancel 469 flights
because of the disruption caused by the terror alert. Ryanair said
it cancelled a total of 265 flights.
---------------------------------------------------------------------------

    The FAA's safety philosophy is to address aviation safety threats
whenever practicable solutions are found, especially when dealing with
intractable and catastrophic risks like fuel tank explosions that are
virtually certain to

[[Page 42447]]

occur. Thus, now that solutions are reasonably cost effective, we have
determined that it is necessary for safety and in the public's best
interest to adopt these requirements.

II. Background

A. Summary of the NPRM

    On November 23, 2005, the FAA published in the Federal Register the
Notice of Proposed Rulemaking (NPRM) entitled ``Reduction of Fuel Tank
Flammability in Transport Category Airplanes'' (70 FR 70922). This NPRM
is the basis for this final rule.
    In the NPRM, we proposed steps to be taken by manufacturers and
operators of transport category airplanes to significantly reduce the
chances of a catastrophic fuel tank explosion. The proposal followed
seven years of intensive research by the FAA and industry into
technologies designed to make fuel tanks effectively inert. Inerting
reduces the amount of oxygen in the fuel tank vapor space so that
combustion cannot take place if there is an ignition source. Although
the NPRM did not specifically direct the adoption of inerting
technology, it did propose a performance-based set of requirements for
reducing fuel tank flammability to an acceptably safe level.
    We proposed regulatory changes to require manufacturers and
operators to reduce the average fuel tank flammability exposure in
affected fleets. The main premise of the proposal was that a balanced
approach to fuel tank safety was needed that provides both prevention
of ignition sources and reduction of flammability of the fuel tanks.
While the focus of the NPRM was on airplanes used in passenger
operations, we requested comments on whether the new requirements
should also be applied to all-cargo airplanes.
    We also proposed changes to expand the coverage of part 25 by
making manufacturers generally responsible for the development of
service information and safety improvements (including design changes)
where needed to ensure the continued airworthiness of previously
certificated airplanes. This change was proposed to ensure that
operators would be able to obtain service instructions for making
necessary safety improvements in a timely manner.
    As to fuel tank flammability specifically, we proposed to require
manufacturers, including holders of certain airplane TCs and of
auxiliary fuel tank supplemental type certificates (STCs), to conduct a
flammability exposure analysis of their fuel tanks. We proposed a new
Appendix L (now Appendix N) to part 25 that provides a method for
calculating overall and warm day fuel tank flammability exposure. Where
the required analyses indicated that the fuel tank has an average
flammability exposure below 7 percent, we anticipate no changes would
be required. However, for the other fuel tanks, manufacturers would be
required to develop design modifications to support a retrofit of the
airplane fuel tanks. Under the NPRM, the average flammability exposure
of any affected wing tank would have to be reduced to no more than 7
percent. In addition, for any normally emptied fuel tank (including
auxiliary fuel tanks) located in whole or in part in the fuselage,
flammability exposure was to be reduced to 3 percent, both for the
overall fleet average and for operations on warm days.
    We also proposed to set more stringent safety levels for certain
critically located fuel tanks in most new type designs, while
maintaining the current, general standard under Sec.  25.981 for all
other fuel tanks. The expectation was that the design of most normally
emptied and auxiliary tanks located in whole or in part in the fuselage
of transport category airplanes would need to incorporate some form of
FRM or IMM.
    In Appendix M to part 25, we proposed to adopt detailed
specifications for all FRM, if they were used to meet the flammability
exposure limitations. These additional requirements were designed to
ensure the effectiveness and reliability of FRM, mandate reporting of
performance metrics, and provide warnings of possible hazards in and
around fuel tanks.
    We also proposed that TC holders for specific airplane models with
high flammability exposure fuel tanks be required to develop design
changes and service instructions to facilitate operators' installation
of IMM or FRM. Manufacturers of these airplanes would also have to
incorporate these design changes in airplanes produced in the future.
In addition, design approval holders (TC and STC holders) and
applicants would have to develop airworthiness limitations to ensure
that maintenance actions and future modifications do not increase
flammability exposure above the limits specified in the proposal. These
design approval holders would have to submit binding compliance plans
by a specified date, and these plans would be closely monitored by the
design approval holders' FAA Oversight Offices to ensure timely
compliance.
    Lastly, the proposal would require affected operators to
incorporate FRM or IMM for high-risk fuel tanks in their existing fleet
of affected airplane models. The proposal would have applied to
operators of airplanes under parts 91, 125, 121, and 129. Operators
would also have to revise their maintenance and inspection programs to
incorporate the airworthiness limitations developed under the NPRM. We
also proposed strict retrofit deadlines, which were premised on prompt
compliance by manufacturers with their compliance plans.
    The NPRM contains the background and rationale for this rulemaking
and, except where we have made revisions in this final rule, should be
referred to for that information.

B. Related Activities

    On November 28, 2005, the FAA published a Notice of Availability of
Proposed Advisory Circular (AC) 25.981-2A, Fuel Tank Flammability, and
request for comments in the Federal Register (70 FR 71365). The notice
announced the availability of a proposed AC that would set forth an
acceptable means, but not the only means, of demonstrating compliance
with the provisions of the airworthiness standards set forth in the
NPRM. On March 21, 2006, the FAA published a notice that extended the
comment period as a result of an extension of the NPRM's comment period
to May 8, 2006 (71 FR 14281).

C. Differences Between the NPRM and the Final Rule

    As a result of the comments received and our own continued review
of the proposals in the NPRM, we have made several changes to the
proposed regulatory text. The majority of these changes will be
discussed in the ``Discussion of the Final Rule'' section below. The
following is a summary of the main differences between the NPRM and
this final rule.
    1. Design Approval Holders. The design approval holder (DAH)
requirements proposed in the NPRM as subpart I of part 25 are now
contained in new part 26. This was done to harmonize with the
regulatory structure of other international airworthiness authorities.
We also revised the applicability for the retrofit requirement so the
DAH requirements do not apply to airplanes manufactured before 1992.
The effect of this change is that DAHs will not have to develop FRM or
IMM for many older airplane models that do not have significant
remaining useful life in passenger operations. We revised the
compliance times for DAHs to

[[Page 42448]]

develop and make available service instructions for FRM or IMM by
replacing specific compliance dates with a compliance time of 24 months
after the effective date of this rule for all affected airplane models.
We have also made some changes, discussed later, to the compliance
planning sections of the DAH requirements.
    2. Auxiliary Fuel Tanks. We have learned that few auxiliary fuel
tanks installed under STCs and field approvals remain in service, and
we need to obtain additional information to decide whether the risks
from these tanks justify retrofit requirements. Therefore, we have
removed the requirements for an FRM or IMM retrofit for these tanks.
    3. Impact Assessments. We limited the requirement for impact
assessments for auxiliary fuel tanks to airplanes with high
flammability tanks for which an FRM is required (i.e., Heated Center
Wing Tank airplanes).
    4. All-Cargo Airplanes. We retained the proposal to exclude all-
cargo airplanes from the requirement to retrofit high flammability
tanks with FRM or IMM. However, we added a requirement that when any
airplane that has an FRM or IMM is converted from passenger use to all-
cargo use, these safety features must remain operational. We also added
a requirement that newly manufactured all-cargo airplanes must meet the
same requirements as newly manufactured passenger airplanes. We revised
Sec.  25.981 to remove the exclusion of all-cargo airplanes so that any
newly certificated transport category airplane, regardless of the type
of operation, must meet the same safety standards.
    5. Part 91 Operators. The proposed rule would have applied to
operators under part 91, which is limited to private use operations.
However, the final rule does not include part 91 requirements.
    6. Retrofit Requirements for Operators. We have added a provision
for air carrier operators that allows a one year extension in the
compliance time to retrofit of their affected fleets if they revise
their operations specifications and manuals to use ground conditioned
air \8\ when it is available. Instead of requiring retrofit for all
airplanes with high flammability fuel tanks, we revised the operating
rules to prohibit operation of these airplanes in passenger service
after 2016 unless an FRM or IMM is installed. This approach gives
operators the option of converting these airplanes to all-cargo
service. We also prohibit the operation of airplanes with high
flammability fuel tanks produced after 2009 unless they are equipped
with FRM or IMM. This requirement parallels the proposed production
cut-in requirement, but also applies to foreign manufactured airplanes.
Finally, instead of requiring retrofit of high flammability auxiliary
fuel tanks, we prohibit installation of auxiliary fuel tanks after 2016
unless they comply with the new requirements of Sec.  25.981.
---------------------------------------------------------------------------

    \8\ ``Ground conditioned air'' is temperature controlled air
used to ventilate the airplane cabin while the airplane is parked
between flights.
---------------------------------------------------------------------------

III. Discussion of the Final Rule

A. Summary of Comments

    The FAA received over 100 comment letters to the proposed rule and
guidance material. These letters covered a wide spectrum of topics and
range of responses to the rulemaking package, which will be discussed
more fully below. While there was much support for the general intent
of the rule changes and the guidance material, there were several
requests for changes and for clarification.

B. Necessity of Rule

1. Estimates/Conclusions Supporting Need for Rule
    In the NPRM and its supporting documents, we noted several
estimates and conclusions that we used to determine the necessity and
content of this rule. We received comments on the following
assumptions:
     The historical accident rate for heated center wing tank
(HCWT) airplanes is 1 accident per 60 million hours of flight (before
implementing corrective actions following TWA 800).
     That SFAR 88 and other corrective actions would prevent 50
percent of future fuel tank explosions.
     That Boeing and Airbus airplanes have an equal risk of an
explosion.
     That a HCWT, depending upon the airplane model and its
mode of operation, is explosive 12 to 24 percent of the time.
     That the rate of accidents directly correlates to
flammability exposure.
    Based on the comments received, we have changed the historical
accident rate estimate to 1 accident per 100 million hours. This change
does not affect our conclusion that the historical accident rate for
HCWT airplanes supports the need for this rule. As for the other
estimates and conclusions, we have not changed these in the final rule.
a. Historical (pre-TWA 800) Accident Rate
    Airbus, the Air Transport Association (ATA), Alaska Airlines
(Alaska), the Association of Asia Pacific Airlines (AAPA), the
Association of European Airlines (AEA), Boeing, Cathay Pacific Airways
(Cathay), Delta Air Lines (Delta) and FedEx stated that the historical
accident rate of 1 accident every 60 million fleet operating hours was
too high. Most of these commenters recommended a rate of 1 accident per
140 million hours. Their proposed rate is based on the number of
accidents and the total fleet hours for heated center wing tank (HCWT)
airplanes through 2005 (3 accidents over 430 million hours). Several of
these commenters also noted that this rate is closer to the
conservative estimate in the MITRE Corporation's assessment of the
FAA's accident prediction/avoidance model (1 accident every 160 million
hours).\9\
---------------------------------------------------------------------------

    \9\ The Mitre assessment of the FAA accident prediction
methodology is included as Appendix H of the Initial Regulatory
Evaluation and is available in the docket for this rulemaking
(Document Number FAA-2005-22997-3).
---------------------------------------------------------------------------

    Boeing proposed a rate of 1 accident every 100 million hours.
Boeing's analysis also started with the number of accidents and the
total fleet hours for HCWT airplanes through 2005. However, Boeing
recognized that some of the improvement since 2001 may be attributable
to the FAA/industry focus on ignition prevention and concluded that the
rate of 1 accident every 100 million hours more accurately represents
the pre-TWA 800 rate.
    FedEx stated that, from a historical basis, 140 million hours would
be a correct mean time between accidents. However, FedEx noted that a
more conservative estimate closer to 100 million hours would still be
acceptable.
    In a related comment, ATA questioned our use of flight hours as the
measure of exposure to risk. ATA noted that two of the historical
accidents did not occur in flight. Therefore, flight hours may
understate exposure and overstate risk. ATA concluded that these
accidents support the use of block hours or some other measure that
accounts for time on the ground (and would lower the accident rate by
about 16 percent).
    We agree that the accident rate used in the NPRM was too high and
needs adjustment. While the rate of 1 accident every 140 million hours
is correct if you only use the total fleet hours for HCWT airplanes
through 2005, it fails to consider the beneficial effects of FAA/
industry action following the TWA 800 accident. Since that accident, we
have issued many ADs to address specific findings of unsafe conditions
that could produce fuel tank ignition sources. In addition, the Fuel
Tank Safety Rule, of which SFAR 88 was a part, was issued in 2001 to
establish a systematic process for identifying and eliminating ignition

[[Page 42449]]

sources. Many of the improvements resulting from these actions have
been implemented in the transport airplane fleet, and the improved
safety record since TWA 800 is largely attributable to them. While the
commenters acknowledge that these actions have been effective at
preventing future accidents, most of them failed to reduce their
proposed historical rate accordingly to address these benefits. In
contrast, Boeing's recommended rate considers the benefits of these
actions (which we calculate covers about 170 million hours).
    We believe that an accident rate of 1 per 100 million hours is an
accurate calculation of the historical accident rate before
implementation of post-TWA 800 ignition prevention actions. Therefore,
we used this rate in developing this final rule and its supporting
documents. However, this change does not affect our conclusion that the
historical accident rate for HCWT airplanes supports the need for this
rule. We continue to believe that the risk of an accident is too high.
    Several commenters referred to the rate in the MITRE Corporation's
report (1 accident every 160 million hours). This rate includes
operations of airplanes without HCWT. Recommendations resulting from
MITRE's review included a suggestion that only fleet hours from
airplanes with HCWT be used in the accident prediction model. We agreed
with this recommendation and have adjusted the accident rate
accordingly.
    Finally, we do not agree with ATA's conclusion that the use of
flight hours to predict future accidents results in an overstated risk.
Both the past accident rate and the future predicted number of
accidents were based upon the number of flight hours of airplanes with
high flammability fuel tanks, and in both cases the number of flight
hours does not include ground time. The ratio of flight time to ground
time is unlikely to change significantly in the future because the
average flight length and the amount of time spent on the ground before
and after each flight are unlikely to change significantly. Therefore,
whether past and future accident rates are stated in terms of flight
time only or flight time plus ground time, the projected future
accident rates would predict the same number of accidents over any
given time period.
b. SFAR 88 Effectiveness Rate
    In the NPRM and its supporting documents, we estimated that SFAR 88
would prevent 50 percent of future fuel tank explosions (although we
also conducted a sensitivity analysis using effectiveness rates of 25
and 75 percent). ATA stated that the 50 percent effectiveness rate was
without basis or explanation and recommended a rate of 90 percent.
Airbus recommended an effectiveness rate in the range of 75 to 90
percent. If these higher rates are used, ATA and Airbus noted the
safety benefits of the proposed rule are insufficient to justify the
costs, and they requested that we withdraw the NPRM.
    Predicting the effectiveness of ignition prevention actions is
challenging, since many ignition sources are the result of human error,
which cannot be precisely predicted or quantitatively evaluated.
Despite extensive efforts by the FAA and industry to prevent ignition
sources, we continue to learn of new ignition sources. Some of these
ignition sources are attributable to failures on the part of
engineering organizations to identify potential ignition sources and
provide design changes to prevent them. Others are attributable to
actions by production, maintenance, and other operational personnel,
who inadvertently compromise wiring and equipment producing ignition
sources. Regardless of the causes, we believe that ignition prevention
actions, while necessary, are insufficient to eliminate ignition
sources.
    Based on the recently discovered ignition sources discussed
earlier, we continue to believe that an assumed effectiveness rate of
50 percent is reasonable and appropriate. In its study on SFAR 88
effectiveness, Sandia National Laboratories concluded that our estimate
of 50 percent was reasonable, and the value of 75 percent effectiveness
assumed in the initial Aviation Rulemaking Advisory Committee (ARAC)
report was overly optimistic. While the report of the ARAC Fuel Tank
Inerting Harmonization Working Group \10\ initially assumed an
effectiveness of 75 percent, the report was later amended to use a
range of effectiveness between 25 to 75 percent because of the
uncertainty in predicting the effectiveness.
---------------------------------------------------------------------------

    \10\ Document Number FAA-22997-6 in the docket for this
rulemaking.
---------------------------------------------------------------------------

    Finally, since ATA did not submit any data to substantiate that a
higher effectiveness rate is more reasonable, we believe the post-SFAR
88 service experience supports the use of a range of effectiveness
between 25 to 75 percent and a median value of 50 percent.
c. Boeing and Airbus Airplanes Have an Equal Risk of an Explosion
    We concluded that all airplanes with HCWT had similar levels of
fuel tank flammability and the associated increase in the likelihood of
a fuel tank explosion. We based the SFAR 88 effectiveness estimates on
the HCWT fleet as a whole. We did not differentiate among airplane
models based upon design differences that could affect the likelihood
of an ignition source forming.
    AEA, Airbus, Frontier Airlines (Frontier), the Air Safety Group UK,
Singapore Airlines (Singapore), BAE Systems (BAE), TDG Aerospace (TDG)
disagreed with this proposal and argued that the risk of an explosion
is lower for Airbus airplanes. These commenters noted that fuel tank
designs for those airplanes that experienced a fuel tank explosion are
at least a decade older than Airbus' designs. Airbus argued that its
airplanes use newer technology and design philosophies that have
incorporated the lessons learned from prior designs. BAE and two
individuals suggested that we address fuel tank flammability by issuing
ADs to address specific design shortfalls in the two airplane types
that have experienced fuel tank explosions (i.e., the Boeing 737 and
747 series airplanes).
    While we did note differences between the designs and technologies
used by Boeing and Airbus, we concluded that the risk of an explosion
was equal for Boeing and Airbus airplanes based on similarities in
their fuel tank designs and service history. We found that both
manufacturers have similar problematic fuel tank design features. For
example, air conditioning equipment is located below the center wing
tank in both manufacturers' designs (and HCWT have flammability
exposure well above that of a conventional unheated aluminum wing
tank). Likewise both manufacturers locate fuel gauging systems with
capacitance measuring probes inside the fuel tank, and associated
wiring to the probes enters the fuel tank from outside. These wires are
co-routed with high-energy wiring to other airplane systems that have
sufficient energy to cause an ignition source inside the fuel tanks.
Finally, high-energy electrical fuel pumps are located within the fuel
tanks and are fuel-cooled and manufactured by the same component
suppliers. Arcing of the pump could cause a spark inside the fuel tank
or could create a hole at the pump connector, causing a fuel leak and
an uncontrolled fire outside of the tank.
    As for the service history and design reviews of Airbus airplanes,
we found numerous situations that indicate a risk of an explosion
similar to those aboard Boeing airplanes, including:
     The electrical bonding straps used on Airbus airplanes
have been reported

[[Page 42450]]

to degrade due to corrosion; the bonding jumpers used by Boeing are
made of a different material that does not corrode.
     All fuel pumps on Boeing airplanes are being modified to
incorporate ground fault power interrupters, whereas only pumps that
can arc directly into the fuel tank ullage are being modified to
incorporate ground fault power interrupters on Airbus airplanes.
     The safety assessments conducted by both manufacturers
resulted in very similar numbers of ignition sources that required
modifications to their airplanes.
     After the SFAR 88 assessments were completed, we learned
that fuel quantity indicating probes within the fuel tanks of Airbus
A320 airplanes could be an ignition source due to sparks that could be
created following a lightning strike. This resulted in the issuance of
AD 2006-06-14.
     After the SFAR 88 assessments were completed, we learned
that the improper installation of a screw inside the fuel pumps of
Airbus A320 airplanes could result in the screw loosening and falling
into the pump electrical windings. This could create a spark and ignite
vapors in the pump that could exit the fuel pump housing into the fuel
tank through the hole created when the screw fell out of the housing.
This resulted in the issuance of AD 2006-12-02.
    The recent discovery of the ignition sources in Airbus A320
airplanes is evidence that unforeseen failures will occur in the future
that can result in ignition sources on Airbus airplanes. The Airbus
fleet has significantly fewer flight hours than Boeing airplanes and,
as the Airbus airplanes age, we expect to see more unforeseen failures.
Therefore, based on design similarities and service history, we see no
reason to differentiate between Airbus and Boeing airplanes. This rule
requires all affected manufacturers to determine the fuel tank
flammability exposure of their airplanes by assessing them against
performance-based requirements that specify a flammability exposure
that we have determined provides an acceptable level of safety.
Additional action is only required for those airplanes that do not meet
the required level of fuel tank flammability safety.
d. ARAC Flammability Exposure Data
    Airbus and AEA both commented that the ARAC flammability exposure
data cited in the NPRM are incorrect and need to be reduced based on
updated data developed by both Boeing and Airbus. They said this
reduction is important since the lower data reduce the level of safety
improvement that can be achieved by this rule from the FAA's intended
``order of magnitude'' (factor of 10) to a safety improvement in the
range of only a factor of 7.7 to 2.7, depending on the model used.
Airbus also objected to our conclusion that a HCWT, depending upon the
airplane model and its mode of operation, is explosive 12 to 24 percent
of the time. Airbus requested that this be corrected to reflect the
latest industry estimates for Airbus products (i.e., 8 to 12 percent)
and 16 to 18 percent for other manufacturers.
    We acknowledge that the flammability exposure data cited in the
NPRM may not reflect current values. However, Boeing and Airbus
submitted those data to us as part of the SFAR 88 reviews. While we
agree with Airbus that more recent information has indicated lower
flammability for HCWTs, we do not agree that the more recent values
should be used since the manufacturers have not submitted a validated
analysis using the revised flammability assessment techniques (as
defined in Sec.  25.981) to support its figures. Changes to the method
for calculating fuel tank flammability, such as airplane ground times
used in the Monte Carlo analysis required by Appendix N may result in
additional variations in flammability calculations. Since flammability
reduction was first considered by the aviation industry, the
flammability values quoted by airplane manufacturers have varied
considerably. These variations were the result of the method used to
calculate the flammability of the fuel tanks and more accurate fuel
tank temperature data based upon flight tests. For example, the first
ARAC determined values ranged from 10 to 50 percent for generic
airplanes equipped with HCWT. After the conclusion of this activity,
Airbus was quoted in Air Safety Week as stating the A310 HCWT having a
flammability exposure of 4 percent. In 2001, as part of the SFAR 88
compliance, Airbus submitted flammability values to the European
Aviation Safety Agency (EASA) and to us that ranged between 12 and 23
percent.
    We recognize that as methods for measuring fuel tank flammability
are refined, it is likely that calculated flammability exposure will
also change. These refinements also apply to the conventional unheated
aluminum wing tanks that ARAC used as the baseline for determining an
acceptable exposure. We now know that the exposure of these tanks is
considerably lower than originally estimated by ARAC. However, none of
this new information changes the findings of ARAC that HCWTs have
significantly higher risk of fuel tank explosions, or that the
reduction in flammability exposure would be on the order of a factor of
10. Therefore, we do not believe that these refinements change the
overall conclusion that certain fuel tanks that are affected by this
rule have significantly higher flammability exposure than conventional
unheated aluminum wing tanks. No change has been made to the final rule
as a result of these comments.
e. Accidents Directly Correlate to Flammability Exposure
    Airbus did not agree with the assumption that the rate of accidents
directly correlates to flammability exposure. Airbus contended that the
risk of ignition source development must also be considered when
evaluating the benefits of flammability reduction.
    We agree with Airbus that the overall risk of a fuel tank explosion
includes both the potential for an ignition source and the likelihood
that the fuel tank will be flammable when an ignition source occurs.
There may be differences in the likelihood of an ignition source
occurring between different airplane types, but these differences would
be very difficult to quantify. We have no statistically significant,
validated data that could be used to establish rates of development of
ignition sources for different airplane types. As discussed in the
Sandia report, there is a wide variation in the predicted rate of
ignition sources developing in fuel tanks and there is no industry
agreement on the rate that should be used for individual airplane
designs. In addition, recent service history shows there have been a
number of ignition sources that have developed following the TWA 800
accident in both Airbus and Boeing airplane models.
    Given this lack of data and consensus on ignition source risks, we
continue to believe that correlating accident rates with flammability
exposure is the most appropriate analytical approach.
2. Additional Research Needed
    Airbus, AAPA, AEA, EASA, Iberia Maintenance and Engineering
(Iberia), Singapore and Virgin Atlantic Airways (Virgin) stated that
this rulemaking is premature because the risks of additional fuel tank
explosions are not adequately defined. These commenters argued that
additional research is necessary to better understand flammability,
SFAR 88 effectiveness and the risks of additional explosions. In a
related comment, the International Federation Victims of Aviation
Accident (IFVAA) stated that additional research should be performed to
identify

[[Page 42451]]

technology that would completely eliminate, not just reduce, fuel tank
flammability.
    We think it would be a mistake to delay this rule to conduct
additional research. Service history and the recent occurrences of
ignition sources described earlier demonstrate that the risk of future
explosions remains significant. In addition, we believe that additional
research would not provide any useful information that would change our
finding that flammability reduction, in combination with the SFAR 88
measures, is needed to prevent such explosions. As for IFVAA's comment,
we consider existing flammability reduction means highly effective and
sufficient to reduce the risk of fuel tank explosions to an acceptable
level. While further research might identify even better solutions, the
resulting delay would deprive the public of the benefits of these
currently available safety improvements.
3. Consistent Safety Level With Other Systems
    Airbus commented that SFAR 88 improvements, together with the
current rate of occurrence, put fuel tank safety on the order of one
accident for every billion flight hours (i.e. 10-9 accidents
per flight hour) which is consistent with safety objectives of other
critical airplane systems.\11\ Airbus argued that this rule requires
fuel tanks to go to a higher level of safety than other critical
systems and that this is inconsistent with the overall risk.
---------------------------------------------------------------------------

    \11\ This is the quantitative probability measure (one in one
billion) of an event that is ``extremely improbable'' as that term
is used in Sec.  25.1309 and other part 25 airworthiness standards.
See AC 25.1309.
---------------------------------------------------------------------------

    Application of existing safety standards to prevent ignition
sources that are similar to those applied to other systems has not
resulted in an acceptable level of safety, and we have determined that
limiting fuel tank flammability is also needed. Fuel tank explosions
are unacceptably occurring at a rate greater than 10-9 per
flight hour and the recent events described above show that
unanticipated failures continue to result in ignition sources within
airplane fuel tanks. To protect the flying public, we have developed a
``fail safe'' policy for fuel tank safety that includes both ignition
prevention and flammability reduction to reduce fuel tank explosion
risk to an acceptable level.
4. Human Errors
    AEA stated that human errors are not new and should not be used to
justify this rule. AEA pointed out that TC holders are obliged to
consider human error during airplane design to mitigate errors. In
addition, continuing airworthiness instructions (e.g., maintenance
manuals) highlight safety considerations where necessary. AEA also
contended that, in the 17 accidents cited by the FAA in the NPRM, there
is no evidence that any were caused by the introduction of an ignition
source through human error. Finally, AEA noted that human errors will
always be a factor in aviation safety, particularly when introducing
added complexity such as an inerting system.
    We agree with AEA that human errors are not a new phenomenon and
that the introduction of new systems on airplanes can have unintended
consequences resulting from human error. We also believe the safety
benefits of FRM or IMM is warranted. Service history shows the current
regulations do not provide an adequate mitigation of human errors for
fuel tank systems. Ignition sources continue to occur even though
designers have conducted analyses that concluded ignition sources would
not occur. Earlier in this document, we discussed numerous ignition
sources that have recently developed in airplanes that had previously
been shown by safety assessments to have features that would prevent
ignition sources from developing. These ignition sources were caused by
errors in defining assumptions in safety assessments, as well as in the
design, manufacture and maintenance of these airplanes. These events
show that an additional layer of protection (in the form of FRM or IMM)
is needed to prevent future fuel tank explosions.
5. Explosion Risk Analysis
    American Trans Air commented that the assumptions made in the
explosion risk analysis were erroneous and not within the range of
reasonable values. American Trans Air recommended that a completely new
analysis of the fuel tank explosion risk be undertaken. This new
analysis should utilize widely accepted assumptions, including taking
into account:
     The history of particular type designs.
     The actual ignition risk potential (i.e., potential
ignition sources not in the ullage are either exempted, or
substantially discounted in the analysis).
     Actual ignition energies, applying these energies to the
potential ignition sources.
     The definitions and assumptions of fuel-air vapor mixtures
that have been further derived and applied on an individual type design
basis.
    We agree with the commenter that the assumed fuel air vapor mixture
should be based upon the individual fuel tank design, and we included
variations in the pressure and temperature of the fuel when developing
the fuel tank flammability model. This factor is already accounted for
in the Monte Carlo method defined in Appendix N. As for the other
assumptions offered by American Trans Air, they cannot be used in an
analysis, because there is a wide variation in the possible values.
6. Special Certification Review Process vs. Rulemaking
    American Trans Air commented that if an analysis identifies type
designs still found to have unacceptable risk after all SFAR 88
alterations have been executed, an appropriate response to address the
remaining at-risk type designs may be the use of the special
certification review process. American Trans Air noted that there
appears to be wide variability in the risk between type designs, and
concluded that generalized rulemaking is inappropriate at this time.
    We do not agree that we should address each type design with
unacceptable flammability risk by special certification review and then
by an appropriate AD. Through careful study, we have determined that
the flammability risk on many airplanes is too high. To address this
risk, we have created an objective design standard by which all
airplanes can be measured. If airplanes currently meet this design
standard, no action will be required. The TC holder for those airplanes
that do not meet it will have to make only those changes that bring
that airplane model into compliance. We have determined that the
uncertainty involved in the elimination of ignition sources requires
reduced flammability to acceptably reduced tank explosion risk, and the
most effective and efficient way to address this issue is through the
rulemaking process.
7. Flammability Reduction Means (FRM) Effectiveness
    In the NPRM, we said lowering the flammability exposure of the
affected fuel tanks in the existing fleet and limiting the permissible
level of flammability on new production airplanes would result in an
overall reduction in the flammability potential of these airplanes of
approximately 95 percent. Airbus and AEA commented that we overstated
the potential benefits of flammability reduction measures by a factor
between 4 and 7. They said we used a factor of 20 (95 percent) for the

[[Page 42452]]

reduction in flammability exposure achieved by reducing the
flammability of HCWT to 3 percent or less. They said the subsequent
reduction in flammability will be in the order of a factor of three to
five and not a factor of 20. Therefore, the number of accidents
prevented would consequentially be less than projected by the FAA.
Airbus also said the FAA appears not to have considered the
effectiveness of the FRM itself, which it said is in the order of 67 to
87 percent by latest industry estimates. Therefore, Airbus suggests
that the Initial Regulatory Evaluation (IRE) is incomplete and should
be revised to include this key parameter.
    The 95 percent value used in the NPRM was not based on the ratio of
fuel tank fleet average flammability exposure before and after
implementing the requirements of this rule. It was derived by
qualitatively evaluating the effectiveness of an FRM in preventing fuel
tank explosions that would not be prevented by ignition prevention
measures.
    When an FRM is installed on a fuel tank, it must meet both the 3
percent fleet average flammability exposure and also the 3 percent warm
day (specific risk) flammability exposure requirements.\12\ For the
warm day requirement, the flammability exposure must be below 3 percent
during ground and takeoff/climb conditions for those days above 80
degrees F when the FRM is operational. These are the conditions when
fuel tanks tend to have the highest flammability exposure and when the
accidents discussed earlier occurred.
---------------------------------------------------------------------------

    \12\ The overall time the fuel tank is flammable cannot exceed 3
percent of the Flammability Exposure Evaluation Time (FEET), which
is the total time, including both ground and flight time, considered
in the flammability assessment defined in proposed Appendix N. As a
portion of this 3 percent, if flammability reduction means (FRM) are
used, each of the following time periods cannot exceed 1.8 percent
of the FEET: (1) When any FRM is operational but the fuel tank is
not inert and the tank is flammable; and (2) when any FRM is
inoperative and the tank is flammable.
---------------------------------------------------------------------------

    The combination of the warm day requirement and the fleet average
flammability requirement results in an FRM with overall flammability
reduction benefits that are significantly higher than those estimated
by the commenters. Since the NPRM was issued, we have reviewed and
approved FRM designs and have found the performance exceeds the
certification limits. When the FRM is operating, the fuel tanks are
rarely flammable. So, the major risk of fuel tank flammability occurs
when the system is inoperative and this time is limited to a maximum of
1.8 percent of the Flammability Exposure Evaluation Time (FEET).
Historically, designers provide a safety margin in the design so that
the design limits are never exceeded, so we would expect the
flammability to be below this level.
    Another consideration in using a 95 percent effectiveness measure
is the safety improvement noted during warm days. Without any FRM, a
HCWT is flammable about 50 percent of the time during climb. Meeting
both the 3 percent warm day requirement and the 3 percent reliability
requirement results in a flammability exposure of the tank of less than
half of one percent during climb. For an airplane with an initial warm
day flammability of 50 percent, this is a 99 percent reduction in the
flammability during climb. We, therefore, used the 95 percent
effectiveness for flammability reduction in the risk model for the
final regulatory evaluation.

C. Applicability

1. Airplanes With Fewer Than 30 Seats
    The proposed DAH requirements would apply (with some exclusions) to
transport category turbine-powered airplanes approved for a passenger
capacity of 30 or more persons or a maximum payload capacity of 7,500
pounds or more. The UK Air Safety Group disagreed with the proposed
rule's limited applicability because the design of fuel tank systems is
similar for both large and small airplanes. Therefore, it argued that
the potential explosion hazard is equal. The commenter also noted that
EASA's CS-25 regulation for Fuel Tank Ignition Prevention does not make
any distinction based on the number of passenger seats.
    We did not include smaller part 25 airplanes in the DAH
requirements of this final rule because those airplanes generally do
not have high flammability tanks. While some parts of their fuel tank
system designs are similar to those of larger airplanes, we do not
agree that the overall architecture and the risk of a fuel tank
explosion are equal. Data submitted by manufacturers of smaller part 25
airplanes as part of the SFAR 88 analysis show that their airplanes
typically do not have fuel tanks located within the fuselage contour,
and would not be considered high flammability fuel tanks. In most
cases, cool fuel from the wing tanks is drawn into the center wing box,
so the overall flammability is low. In addition, these tanks are not
normally emptied, reducing the amount of ullage.
    Based on these facts, the benefits of including these smaller
airplanes in all of the requirements of this rule are minimal and do
not warrant the cost. However, we do agree that the part 25
requirements applicable to new type designs should be the same for all
transport category airplanes, regardless of size. The cost to design
and produce a new airplane to meet the flammability requirements is
significantly less than that for existing airplanes since the designers
can optimize the performance of the FRM or IMM and integrate it into
the airplane design to minimize costs. Therefore, Sec.  25.981 of this
rule applies to all transport category airplanes regardless of size.
2. Part 91 and 125 Operators
    The NPRM proposed that operators under parts 91, 121, 125, and 129
incorporate FRM or IMM and keep it operational on their affected
airplanes. The AEA and Airbus asked that parts 91 and 125 operations be
excluded and cited corporate use airplanes as an example of operations
where the cost would far exceed the benefit. According to AEA and
Airbus, the cost/benefit analysis for these airplanes, when operated
under part 91 or part 125, would produce results similar to those for
all-cargo airplanes (which are excluded from the retrofit requirements
of this rule).
    We recognize a distinction between part 91 and part 125 operations,
in that part 91 does not allow commercial operations for compensation
or hire, while part 125 does allow such operations, as long as the
operator does not ``hold out'' to the public that they are available
for such operations (in which case they would be required to operate as
an air carrier). For example, many business jets are operated under
part 91 if the operator does not receive compensation for transporting
passengers (e.g., a corporate jet transporting the corporation's
employees). On the other hand, charter companies frequently operate
under part 125 to transport sports teams and other groups for
compensation.
    While we recognize that private owners and operators may choose to
assume the risk of possible fuel tank explosions, we see no reason why
persons flying on commercial charter flights should be exposed to a
greater risk of a fuel tank explosion than passengers flying on
airplanes operated under parts 121 and 129. Commercial charter
passengers are in no better position to recognize and accept the risk
of a fuel tank explosion than are air carrier passengers. Additionally,
the risk and likelihood of a fuel tank explosion are potentially
commensurate with that of the same airplane model operated

[[Page 42453]]

under parts 121 and 129. Therefore, the final rule has been revised to
exclude part 91 operations, but does not exclude part 125 operations.
However, because of the significant safety benefits of this rule, we
encourage part 91 operators to install FRM on their airplanes, and not
to remove it if it is already installed.
3. All-Cargo Airplanes
    In response to our request for comments on the proposed exclusion
of all-cargo airplanes from this rulemaking, we received numerous
comments both supporting and opposing the exclusion. Airbus, the Cargo
Airline Association (CAA), FedEx, ATA, ABX Air (ABX), United Parcel
Service (UPS), and National Air Carrier Association (NACA) agreed that
all-cargo airplanes should be excluded from this rulemaking. The CAA
argued that the risks are lower for cargo carriers due to several
factors:
    a. Cargo operations are predominately night operations with lower
outside ambient temperatures (making fuel tanks less likely to be
flammable).
    b. Cargo operators do not typically run air conditioning packs
prior to takeoff as many passenger operators do.
    c. The CAA members typically operate one to two round trips each
day, which is a lower utilization rate than most passenger airplanes.
    The CAA stated that costs to various airline industry segments
should be considered when proposing any new regulation. The CAA
supported establishing a safety baseline which allows different
operations to meet the baseline in different ways. Based on the factors
articulated above, the CAA maintained the cost/benefit analysis does
not justify its application to cargo airplanes.
    FedEx commented that there is a finite amount of safety dollars and
it is important to use them effectively. As the cost/benefit analysis
does not justify inclusion of all-cargo airplanes, FedEx claimed it is
not permissible to include them under FAA rulemaking authority. ATA
stated that the proposed rule should not apply to all-cargo airplanes,
other than the design rules proposed to prevent modifications that
could increase the flammability exposure of a fuel tank. ABX agreed
with ATA, and noted that the ignition prevention measures of SFAR 88
provide an acceptable level of safety for these airplanes. Finally,
Airbus and UPS based their support for our proposal to exclude cargo
airplanes on the reasons stated in the NPRM.
    On the other hand, the National Transportation Safety Board (NTSB),
the Independent Pilots Association (IPA), the Air Line Pilots
Association (ALPA), the EASA, the Coalition of Airline Pilots
Association (CAPA), Singapore and the National Air Traffic Controllers
Association (NATCA) do not agree that all-cargo airplanes should be
excluded from this rulemaking. While the NTSB, IPA and NATCA
acknowledged that cargo airplanes typically carry fewer people, they
pointed out that these airplanes regularly use airports in densely
populated areas where an accident could have a catastrophic effect for
people on the ground. The NTSB and IPA also cited a recent DC-8 cargo
fire accident where an inerting system might have prevented or
substantially reduced the magnitude of the fire, and a C-5A accident at
Dover Air Force Base where the presence of an inerting system may have
been the reason many lives were saved.
    The IPA also stated that there should be one level of safety for
all part 25 airplanes, and noted that all-cargo airplanes are typically
older (which makes them more susceptible to ignition sources within the
tank). In addition, ADs are being issued on even the newer models to
restrict operations for flammability/ignition concerns.
    ALPA commented that all-cargo airplanes should not be excluded from
critical safety improvements simply because there are fewer fatalities
in a typical crash. ALPA recommended that we apply a firm deadline for
the manufacturers to complete a flammability analysis on all-cargo
airplanes compared to the passenger versions of the same airplane
model.
    EASA did not agree with introducing a new distinction among part 25
products. In EASA's view, the justification for excluding all-cargo
airplanes has yet to be substantiated. CAPA thought the logic of
excluding all-cargo airplanes could be extended to each individual
operator or to all airplanes with differing passenger capacities. For
example, CAPA questioned whether, if operator ``A'' had many more
Boeing 737 airplanes than operator ``B'', would we require Operator
``A'' to use FRM while Operator ``B'' would not have to. CAPA stated
that this same type of flawed logic is being applied to all-cargo
airplanes. In its opinion, the value of pilot lives should not depend
on what is in the back of the airplane. Finally, NATCA commented that
confidence in flying would be diminished if there were a cargo airplane
accident, and we should not set a precedent that sets a different
safety standard based on the intended operation of the airplane.
    Boeing stated that its safety philosophy is to not differentiate
between passenger and cargo airplanes in managing fleet-wide airplane
risk and therefore, did not exclude airplanes designed solely for cargo
operations in their proposed revision to Sec.  25.981(b).
    After reviewing these comments, we have decided that we will not
require existing all-cargo airplanes to meet the retrofit requirements
in this final rule. We did not receive any data on the costs, benefits
or risks for all-cargo airplanes in response to our request in the
NPRM, and we do not have any new data to justify requiring retrofit of
FRM or IMM on the current fleet of all-cargo airplanes. We will
continue to gather additional data regarding these factors and may
initiate further rulemaking action if the flammability of these
airplanes is found to be excessive.
    However, we will require compliance with the requirements of this
final rule for (i) future designs; (ii) the conversion of any passenger
airplane with an FRM or IMM to all-cargo use; and (iii) future
production of all-cargo airplanes. We agree with NATCA and other
commenters with respect to removing the exclusion from Sec.  25.981 of
airplanes designed solely for all-cargo operations. The airworthiness
standards of part 25 do not impose different requirements depending on
the intended use of the airplane. 49 U.S.C. 44701 requires that we
adopt such minimum airworthiness standards as are necessary, and
historically we have recognized that those minimum standards should be
the same for all transport category airplanes, regardless of their
intended use. There are practical reasons for this approach, since the
intended use can change quickly based on business considerations
unrelated to safety. Therefore, we agree that the proposed new design
standards in part 25 should not distinguish between all-cargo and
passenger airplanes.
    The rationale for including a production cut-in for all-cargo
airplanes is based upon the long-term goal of fleet-wide reduction in
flammability exposure to eliminate the likelihood of fuel tank
explosions. In addition to the immediate effects of an accident, we
believe a fuel tank explosion on an all-cargo airplane could have a
significant impact on the aviation industry due to public sensitivity
to terrorist actions. The cost of installing FRM in new production
airplanes is less than the cost of to retrofit airplanes, because the
installation can be efficiently integrated into the production process.
In most cases, this integration will be done for the passenger version
of the same airplane, so additional engineering work will be minimal.
The benefits of production cut-in are also higher than

[[Page 42454]]

for retrofit since the new airplane has a longer life and reduced
flammability will provide safety benefits for the life of the airplane.
    As for conversion airplanes, when older airplanes can no longer be
operated competitively in passenger service, it is common for them to
be converted to all-cargo service. Since many passenger airplanes will
have FRM or IMM already installed as a result of this rule, operators
may be inclined to deactivate or remove the FRM or IMM to reduce
operational costs, if these airplanes are converted to all-cargo
airplanes in the future. We do not believe it would be in the public
interest to allow previously installed systems to be deactivated
because the capital cost to install the systems would already have been
incurred, and the safety benefits of retaining the system would
outweigh any cost savings that might result from deactivating them.
Accordingly, we have revised the operational rules to prohibit
deactivation or removal of FRM or IMM under this scenario.
    The regulatory evaluation for this final rule has been revised to
address these factors and concludes that imposing these requirements on
all-cargo airplanes is cost effective for new designs and newly
produced all-cargo airplanes. Prohibiting deactivation of FRM or IMM on
converted airplanes is also cost effective.
4. Specific Airplane Models
    Proposed Sec.  25.1815(j) listed specific airplane models that
would be excluded from the requirements of proposed Sec.  25.1815 (now
Sec.  26.33). These are airplane models that, because of their advanced
age and small numbers, would likely make compliance economically
impractical. In the NPRM, we asked for comments on other airplane
models that may present unique compliance challenges and should be
excluded from the requirements of this rule. In response to this
request, we received several comments requesting that additional
specific airplane models be excluded from this rule. Given the number
of models identified, we have decided it makes more sense to
``grandfather'' all models manufactured before a certain date. Based on
these comments, we have changed the applicability of the design
approval holder requirements in proposed Sec.  25.1815(a) (now Sec.
26.33(a)) from those airplanes type certificated after January 1, 1958
to those airplanes produced on or after January 1, 1992.
a. Out-of-Production/Low Service Life Remaining Models
    Boeing and Airbus recommended that the rule only apply to airplane
models and auxiliary tanks currently in production, or recently out-of-
production, that have significant numbers in service and will continue
in service well beyond the date when 100 percent compliance is
achieved. Based on this standard, Boeing submitted a list of airplane
models and auxiliary tanks to add to the excluded models in proposed
Sec.  25.1815(j), including the DC-8, DC-9, DC-10, MD-80, MD-90, MD-11,
Boeing 707, 720, 727, 737-100/-200, 747-100/-200/-300 and associated
derivatives, and 737-300/-400/-500 (auxiliary tanks only). Airbus
requested that the Airbus A300/A310 series airplanes be added to the
list based on this standard.
    We acknowledge that there is no reason to require design approval
holders (DAHs) to develop design changes for airplanes that will be
retired before FRM or IMM installation is required by this rule.
Conducting the flammability assessments and developing design
modifications for those airplanes would require significant engineering
resources. More importantly, these airplanes would not benefit from the
development of FRM or IMM, since they would be retired or converted to
cargo operations before the installation of these systems is required.
Therefore, we have limited the applicability of the DAH requirements in
the final rule (proposed Sec.  25.1815(a), now Sec.  26.33(a)) to
airplanes produced on or after January 1, 1992.
    The youngest of the airplanes produced before then would be more
than 25 years old by the time operators would be required to modify
them. We agree with the commenters that the vast majority of these
airplanes would either be retired or converted to cargo service before
they reach that age. This is consistent with current practice. This
limitation has the effect of excluding the Boeing 707, 727, 737-100/200
and 747-100/200/300; the McDonnell Douglas DC-8, DC-9, DC-10, and KC-
10/KDC-10; and the Lockheed L-1011. Airplanes of the other models that
Boeing, Airbus and ATA requested be excluded have been produced on or
after January 1, 1992. For airplanes produced on or after January 1,
1992, the remaining life and likelihood of their continued operation in
passenger service is sufficient to require compliance with the
requirements of this rule.
    To clearly differentiate between airplanes produced before and
after this date, we changed proposed Sec.  25.1815(a) (now Sec.
26.33(a)) to refer to the date when ``the State of Manufacture issued
the original certificate of airworthiness or export airworthiness
approval.'' This information is readily available to the TC holders who
applied for these approvals. We also added a provision to proposed
Sec.  25.1815(d) (now Sec.  26.33(d)) to require the service
information describing FRM or IMM to identify the airplanes that must
be modified under this rule. This will make it readily apparent to
operators which of their airplanes are subject to the retrofit
requirements.
    For airplanes with high flammability tanks produced before 1992,
instead of requiring operators to retrofit these airplanes, we have
added a provision in the operational rules prohibiting passenger
operations of these airplanes after the date by which an operator's
airplanes that are subject to the retrofit requirement must be
retrofitted.\13\ This enables operators to convert these airplanes to
cargo service rather than to retrofit them. If operators of these
airplanes choose to operate them in passenger service past this date,
they could contract with the DAH or a STC vendor to develop an FRM or
IMM to meet the safety requirements of this rule. Without this
provision, the exclusion of airplanes produced before 1992 could have
the unintended consequence of encouraging operators to continue to
operate these airplanes with high flammability tanks in passenger
service, since the retrofit and operating costs of FRM or IMM would not
have to be incurred.
---------------------------------------------------------------------------

    \13\ As discussed later, we are also adding a provision that
allows operators under parts 121 and 129 to extend the compliance
date by one year based on use of ground conditioned air. Operators
using this extension will be able to operate these pre-1992
airplanes in passenger service until they are required to have all
of their post-1991 airplanes retrofitted.
---------------------------------------------------------------------------

    These changes to the DAH and operational rules have the effect of
making the applicability of these requirements different. The DAH
requirements now only apply to airplanes produced on or after January
1, 1992, but the operational rules still apply to all airplanes meeting
the applicability criteria proposed in the NPRM.\14\ Therefore, we have
revised the applicability provisions of the operational rule sections
to incorporate these criteria, rather than referencing the
applicability of the DAH rules.
---------------------------------------------------------------------------

    \14\ With certain listed exceptions, transport category turbine-
powered airplanes type certificated after January 1, 1958, with a
maximum passenger capacity of 30 or more or a maximum payload
capacity of 7,500 pounds or more.
---------------------------------------------------------------------------

    As for Boeing's request to exempt certain auxiliary fuel tanks, as
discussed

[[Page 42455]]

later in more detail, we have retained the requirement to conduct
flammability assessments and impact assessments for auxiliary fuel
tanks. However, we have delayed any action to require retrofit of IMM
or FRM for auxiliary fuel tanks installed under STCs and field
approvals until additional information can be gathered. We agree with
Boeing that any auxiliary fuel tank installed in pre-1992 airplane
models should also be excluded from the need to conduct flammability
assessments, since we have determined we would not take action against
any tank in these airplane models due to their advanced age.
b. Limited U.S. Inventory Models
    Airbus requested that airplanes having a limited U.S. inventory be
excluded from this rule, because the operators of these airplanes would
shoulder a disproportionate impact of non-recurring engineering
expenses needed to design and develop FRM systems. Under this standard,
Airbus asked that the A330-200 (only 11 N-registered airplanes) and the
A340 (no N-registered airplanes) be added to proposed Sec.  25.1818(j).
We cannot agree with the Airbus suggested approach. We have no way to
predict future market conditions in the United States for the A330-200
and A340 model airplanes. Airbus continues to sell these models and
lessors continue to offer them for lease. Based on market conditions,
U.S. operators may add these models to their fleets in larger numbers
and we see no reason why persons flying on these airplanes should be
exposed to a greater risk of a fuel tank explosion. Therefore, we are
not excluding these airplane models from the requirements of this final
rule.
c. Airbus A321
    Airbus and ATA suggested the A321 should be excluded because this
model does not have fuel pumps in the center wing tank, reducing the
risk of a fuel tank explosion. The lack of fuel pumps does not
adequately mitigate the risk of an explosion. There are numerous
potential ignition sources inside fuel tanks that can result from
failure of various components, including the fuel quantity indication
system, motor driven valves, fuel level sensors, and electrical bonds.
In addition, heating of the fuel tank walls by external heat sources
introduces a concern that the hot surface could ignite the vapors in
the tank. The justification provided for excluding this model (because
the center tank does not have motor driven pumps located in the tank)
does not address the overall fuel tank safety issue and would only have
merit if fuel pump failures were the only potential ignition sources.
Therefore, we are not excluding this airplane model from the
requirements of this final rule.
d. Airplanes With Low Flammability Tanks
    The proposed retrofit limit for an acceptable fleet-wide average
flammability exposure was 7 percent. We determined that fuel tanks
having a flammability exposure greater than 7 percent are high
flammability tanks that present a greater risk for fuel tank explosion.
American Trans Air commented that, we stated in the NPRM that some
airplanes have center tanks with a fleet average flammability exposure
that does not exceed 7 percent, including ``the Lockheed L-1011, and
Boeing MD-11, DC10, MD80, and Boeing 727, and Fokker F28 MK100.''
American Trans Air stated that this implies that we have information in
our possession indicating that these airplane models already meet the
proposed flammability limits, and asked that we add these models to the
list of excluded airplanes in proposed Sec.  25.1815(j) (now Sec.
26.33).\15\
---------------------------------------------------------------------------

    \15\ As we discussed above, we have limited the applicability of
the DAH requirements in Sec.  26.33 to airplane models produced on
or after January 1, 1992. This date excludes the Boeing Model 727,
DC-10 and the Lockheed L-1011. The other airplane models mentioned
by the commenter have airplanes produced after 1991 and would be
covered by this rule.
---------------------------------------------------------------------------

    The statement quoted by American Trans Air from the NPRM was based
on previous flammability assessments provided to us for SFAR 88
compliance. These assessments were based upon simplified assessment
methods. For airplanes produced after January 1, 1992, we have retained
the requirement to conduct flammability assessments on these airplanes
to ensure that the earlier assessments are correct and that design
changes for these tanks are not necessary. Once the assessment has been
made, a manufacturer or operator may not need to make any change to the
airplane. This is because the flammability risk assessment may disclose
a level of risk below the threshold required for modification. As
discussed earlier, we are allowing a qualitative assessment for
conventional unheated aluminum wing tanks, which will substantially
reduce the burden for completing the flammability assessments.
5. Wing Tanks
a. General
    Proposed Sec.  25.981 does not apply the same flammability standard
to all fuel tanks, and requires lower flammability limits for ``fuel
tanks that are normally emptied and located within the fuselage
contour.'' The NTSB expressed concern that wing fuel tanks have
exploded, and noted that its safety recommendations were not limited
to:
    (1) Certain types of fuel tanks,
    (2) Tanks with specific types of exposure, or
    (3) Tanks with explosive risks that vary or lessen over time.
    The NTSB stated that we should take action to prevent all tanks
from having flammable fuel-air mixtures in the ullage. The NATCA
agreed, and stated that, to achieve an acceptable level of safety, the
requirements of Sec.  25.981 that apply to new airplanes should
establish the same flammability standard for all fuel tanks regardless
of location. The NATCA supported this suggestion by referencing the
ARAC accident summaries that showed 8 out of 17 fuel tank explosions
have involved wing tanks. The ALPA also expressed concern that certain
wing designs and system installations may result in internal heating of
the wing structure and ultimately the wing fuel tanks. The ALPA stated
that we must insist that those specific installations fall under the
requirements of this rule and that no unsafe flammability exposure
exist in those wing tanks.
    In contrast, Embraer, Bombardier Aerospace (Bombardier), and
American Trans Air opposed incorporation of new flammability standards
for conventional wing tanks. Embraer stated the benefits would be
negligible and would not justify the costs. Embraer maintained that
service history provides ample evidence that conventionally designed
wing tanks inherently provide sufficient protection from fuel tank
ignition when conventional fuels are used and that the current
requirements are adequate. American Trans Air commented that many twin
engine airplane type designs utilize a common fuel system operational
concept that results in low exposure to high energy ignition sources in
the main wing tanks. This exposure is further reduced in airplanes
operated in extended-range twin-engine operations (ETOPS) service, due
to the increased fuel reserves required in these operations.
    The service history of conventional unheated aluminum wing tanks
that contain Jet A fuel indicates that there would be little safety
benefit by further limiting the flammability of these tanks. While
NATCA and the NTSB expressed concern because accidents have occurred in
wing fuel tanks, they did not differentiate service experience based on
fuel type used (JP-4 versus Jet

[[Page 42456]]

A). Our review of the nine \16\ wing tank ignition events shows that 5
of the 9 airplanes were using JP-4 fuel and this type fuel is no longer
used except on an emergency basis in the U.S. Three of the remaining
four events were caused by external heating of the wing by engine
fires, and the remaining event occurred on the ground during
maintenance. To date, there have been no fuel tank explosions in
conventional unheated aluminum wing tanks fueled with Jet A fuel that
have resulted in any fatalities. The flammability characteristics of
JP-4 fuel results in the fuel tanks being flammable a significant
portion of the time when an airplane is in flight. This is not the case
for wing tanks containing Jet A fuel. Therefore, a conventional
unheated aluminum wing tank (that quickly cools in an airplane model
approved for Jet A fuel) would not require FRM or IMM.
---------------------------------------------------------------------------

    \16\ As discussed previously, on May 6, 2006, a ninth wing tank
ignition event occurred.
---------------------------------------------------------------------------

    As proposed, Sec.  25.981(b) maintained the intended flammability
standards for wing tanks that were introduced in 2001, as part of
Amendment 25-102 to part 25.\17\ The proposed text clarified the
existing term ``means to minimize the development of flammable vapors''
by including references to a conventional unheated aluminum wing tank,
or 3 percent average flammability. Therefore, no new flammability
standards are introduced for conventional wing tanks. Fuel tanks
manufactured from materials other than aluminum, or that have unique
features that would not allow cooling of the fuel tank (such as a small
surface area exposed to the air stream) or that are heated (such as by
having warm fuel transferred from another tank) may need FRM to comply
with the previously issued requirements.
---------------------------------------------------------------------------

    \17\ As discussed in the NPRM, Amendment 25-102 revised Sec.
25.981 to require that fuel tank flammability exposure be
``minimized.'' As explained in the preamble to that final rule, the
objective of this requirement is to reduce the flammability exposure
to that of an unheated aluminum wing tank.
---------------------------------------------------------------------------

b. Use of Composite Materials
    Airbus pointed to the industry trend towards the use of composite
materials, which tend to have a lower heat transfer coefficient than
aluminum. These materials act as insulators, slowing down any heating
or cooling effects. Therefore, new TC designs using composite
structures will have a natural flammability exposure greater than an
equivalent conventional unheated aluminum wing tank, and designers will
be forced to implement FRM. The NATCA noted that, with increased use of
composites in wing designs, the assumption that wing tanks cool
adequately may be incorrect.
    We agree that composite materials may act as an insulator that will
not allow fuel tank cooling, resulting in increased flammability.
Limiting fuel tank flammability using FRM may be needed to meet the
flammability exposure of a ``conventional unheated aluminum wing tank''
that is required by Sec.  25.981. Airbus's suggestion that it is
impractical for the rule to mandate the use of inerting for wing fuel
tanks on airplanes with composite fuel tanks is not supported by recent
events. While this rule is performance based and means other than
inerting could be used, inerting has been found to be one means that is
both technically feasible and economically viable. For example, the
Boeing 787 will have wing fuel tanks constructed of composites, and FRM
using nitrogen has been incorporated into the design to reduce the fuel
tank flammability below that of a conventional aluminum wing tank.
6. Auxiliary Fuel Tanks
a. Definition
    In the NPRM, we described auxiliary fuel tanks as tanks that are
installed to permit airplanes to fly for longer periods of time by
increasing the amount of available fuel. The proposed rule defined an
auxiliary fuel tank as one that is normally emptied and has been
installed pursuant to an STC or field approval to make additional fuel
available. We also stated that auxiliary fuel tanks are ``aftermarket''
installations not contemplated by the original manufacturer of the
airplane.
    Airbus and AEA suggested the definition of auxiliary fuel tank
should be clarified. They recommended that we use the generally
accepted definition that is in AC 25.981-2. Boeing also requested that
the definition of an auxiliary fuel tank be revised to more generally
state that it is a fuel tank added to an airplane to increase range
instead of referencing it as one installed pursuant to an STC or field
approval. Boeing noted that an airplane might be delivered with an
Original Equipment Manufacturer designed, manufactured and type
certified auxiliary fuel tank.
    Changes to the regulatory text in proposed subpart I (now part 26)
resulted in eliminating the need for this definition in the final rule.
Therefore, we have deleted the definition of auxiliary fuel tank from
proposed Sec.  25.1803(a) (now Sec.  26.31(a)) and will maintain the
definition in AC 25.981-2.
b. Existing Auxiliary Tanks
    Boeing, Airbus, AEA, and ATA commented that older auxiliary fuel
tanks should be exempt from the requirements of this rule since the
benefits would be small compared to the cost of the retrofits. Boeing
stated by the year 2016, most of the airplanes with auxiliary tanks
installed during production would be over 30 years old. Future service
life is generally thought to be minimal for these older airplanes.
Boeing also commented, based upon feedback received from some
operators, that these operators would deactivate their auxiliary fuel
tanks rather than install FRM or IMM. The ATA added that the favorable
service history (no operational accidents caused by auxiliary tank
overpressures or explosions), operating environment (minimal exposure
to flammable conditions), and proximity to retirement for many of these
tanks makes it unnecessary to include auxiliary tanks in the
applicability of this rule. Finally, Embraer commented that only
auxiliary fuel tanks located close to heat sources and lacking free
stream cooling require the special attention that the rule proposes.
    As discussed previously, we changed the language in proposed Sec.
25.1815 (now Sec.  26.33), which applies to TC holders, to limit its
applicability to airplanes produced on or after January 1, 1992, and
this would include any auxiliary fuel tanks installed by the original
TC holder. Since Sec.  26.35 (formerly Sec.  25.1817) applies only to
design changes to airplanes subject to Sec.  26.33, this change from
the NPRM has the effect of excluding most of the older auxiliary tank
designs installed by STC or field approval, which were approved for
installation on airplanes no longer subject to this rule.
    For those auxiliary tanks approved under STCs or field approvals
(if any) that are still covered under the rule, we believe that most of
these tanks transfer fuel by pressurizing the tank with cabin air. The
increased pressure results in reduced flammability that could be
considered an FRM if the minimum flammability performance requirements
are met. However, we have limited data on the number of these tanks
currently in operation and their age. We currently do not have adequate
information on the flammability exposure or the number and the type of
auxiliary fuel tanks installed under STCs or field approvals to
determine whether to subject them to the requirements of this final
rule. Based upon these limited data, we cannot predict the number of
high flammability auxiliary fuel tanks that

[[Page 42457]]

will be in service in 2016 or the number of airplanes with auxiliary
fuel tanks installed by STC or field approvals that could still be
operational for some period of time past the year 2016.
    While no conclusive evidence has been presented, the commenters
have raised issues worthy of further study. To prevent delaying the
safety benefits of compliance with this rule, we have elected to defer
the portion of this rulemaking that would have required development and
installation of an FRM or IMM for auxiliary fuel tanks installed by STC
or field approvals for further study. We have removed these proposed
requirements from both the DAH and operational rules.
    To assess the possible safety benefits and costs more accurately,
we are requesting further comments regarding information needed to
determine if future action should be taken to address auxiliary fuel
tanks installed by STC or field approvals. The rule retains the
requirements for STC holders to conduct a flammability assessment of
auxiliary fuel tank designs, to conduct an impact assessment of the
auxiliary tank on any FRM or IMM, and to develop the modifications for
any adverse impact that is found. These requirements are still
necessary both to assess the need for further rulemaking and to prevent
increasing the flammability exposure of tanks into which the auxiliary
tanks feed fuel. This could potentially defeat the purpose of requiring
reduced flammability for these tanks. To limit the scope and cost of
the requirement to perform impact assessments, this requirement only
applies to auxiliary tanks approved for installation on Boeing and
Airbus airplanes that we currently are aware will be required to have
FRM or IMM installed.
c. Future Installation of Auxiliary Tanks
    While we are foregoing action to require retrofit of existing
auxiliary fuel tanks, we recognize that this decision could allow
installation of currently approved auxiliary fuel tanks indefinitely,
even if their flammability exposure exceeds those allowed under this
rule. Therefore, we have added a new paragraph to the operational rule
sections \18\ in this final rule to prohibit installation of any
auxiliary tank after the retrofit compliance date (nine years after the
effective date) unless we have certified that the tank complies with
Sec.  25.981, as amended by this rule.
---------------------------------------------------------------------------

    \18\ Sec. Sec.  121.1117(n), 125.509(n), and 129.117(n).
---------------------------------------------------------------------------

d. Request for Comments
    As discussed previously, we have concluded that additional
information is needed before we can determine whether it would be cost
effective to apply the requirements of this final rule to auxiliary
fuel tanks installed under STCs or field approvals. The FAA, therefore,
requests additional comments addressing the following specific
questions:
    1. Which airplanes produced on or after January 1, 1992, with 30
passengers or more or a payload of 7500 pounds, have auxiliary fuel
tanks installed by STC or field approval?
    2. What are the U.S. registration tail numbers of the airplanes
with the tanks installed?
    3. How many of these tanks are installed in airplanes used in all-
cargo operations?
    4. What is the STC holder's name and what are the STC numbers for
these tanks?
    5. How many of these tanks are installed under the Form 337 field
approval process?
    6. Are the tanks operational or deactivated?
    7. How many engineering hours would be required to develop an FRM
or IMM for these tanks?
    8. How much would the parts cost for an FRM or IMM for these tanks?
    9. What would the labor costs be for installing an FRM or IMM in
these tanks?
    10. How many days would it take to install an FRM or IMM in the
affected airplane?
    11. If the FAA required operators to install FRM or IMM, would
those operators modify those tanks accordingly, or would they comply by
simply deactivating those tanks? Please be model-specific for both
passenger and all-cargo airplanes, if possible.
    12. What would be the economic consequences to the operator of
deactivating an auxiliary fuel tank?
    Comments should be submitted to Docket No. FAA-2005-22997 by
January 20, 2009. Comments may be submitted to the docket using any of
the means listed in the Addresses section later in the document.
7. Existing Horizontal Stabilizer Fuel Tanks
    In the NPRM, we stated that horizontal stabilizer fuel tanks are
fuel tanks that may be required to be retrofitted with FRM or IMM. We
understood that these tanks may not cool rapidly, since a large portion
of the fuel tank surface is located within the fuselage contour. Airbus
stated that they do not believe the rule should apply to horizontal
stabilizer fuel tanks, because these types of fuel tanks are low
flammability and, if these tanks are treated as high flammability, the
rule would impose significant additional costs to install FRM or IMM
for these tanks. Therefore, Airbus concluded that we should either
review these additional engineering complications and associated costs
(particularly with respect to retrofit) or apply the same requirements
to these tanks as those proposed for wing tanks not in the fuselage
contour.
    The retrofit requirement of this rule only applies to fuel tanks
that have an average flammability exposure above 7 percent. To the
extent the risk analysis indicates a particular fuel tank actually is a
low risk tank, no further requirements would apply. Some horizontal
stabilizers, including those made by Airbus, are manufactured from
composite material that acts as an insulator. These tanks may also be
used to maintain airplane center of gravity, so warmer fuel may be
transferred into them during flight. These features may result in
flammability exposure that exceeds the 7 percent limit that is used to
establish whether retrofit of an FRM or IMM is required. Tanks
constructed of composites may also exceed the flammability exposure
established for new designs in Sec.  25.981(b).
    The analysis required by this rule will establish the flammability
exposure and determine the need for an FRM or IMM in horizontal
stabilizer fuel tanks. If fuel tanks located within the horizontal
stabilizer are not high flammability tanks, then no FRM or IMM would be
needed and no additional cost would be incurred for retrofit. However,
if an FRM or IMM is required because the tank is determined to be high
flammability, it should be possible, using standard design methods, to
address the technical issues. For example, the pressure drop mentioned
by Airbus can be addressed by using a properly sized and designed FRM
so that adequate nitrogen can be supplied to any affected tank. This
can be done using available technology and with costs that are
consistent with those for other tanks considered in the regulatory
evaluation. Airbus provided no technical justification for its
assertion to the contrary.
8. Foreign Persons/Air Carriers Operating U.S. Registered Airplanes
    Airbus, EASA, and the UK Civil Aviation Authority (UKCAA) requested
a change to the wording of proposed Sec.  129.117(a). This change would
clarify that the applicability of this rule is

[[Page 42458]]

limited to foreign persons and foreign air carriers operating U.S.
registered transport category, turbine powered airplanes for which
development of an IMM, FRM or Flammability Impact Mitigation Means
(FIMM) is required under proposed Sec. Sec.  25.1815, 25.1817 or
25.1819 (now Sec. Sec.  26.33, 26.35, and 26.37). Their understanding
is that the paragraph is not intended to apply to airplanes registered
outside of the United States.
    As provided in Sec. Sec.  129.1(b) and 129.101(a), the commenters
are correct that Sec.  129.117 would not apply to aircraft registered
outside the United States. To clarify our intent, we have revised Sec.
129.117(a) to include the words ``U.S. registered.''
9. Airplanes Operated Under Sec.  121.153
    In the proposed rule, the FAA requested comments on whether
categories of airplane operations other than all-cargo operations
should be excluded. In response to our request, AEA and Airbus noted
that Sec.  121.153 permits the operation, by U.S. airlines, of
airplanes registered in another International Civil Aviation
Organization (ICAO) member states under specified circumstances. They
said that, while history shows that the use of the Sec.  121.153
provisions is relatively rare, it can provide important flexibility
when unusual circumstances dictate the urgent need of replacement
airplanes for U.S. carriers. Given the small effect of excluding
airplanes leased under the provisions of Sec.  121.153 from any
requirements of the proposed rule, the commenters recommend that they
be excluded from applicability provisions of the proposed rule.
Otherwise, they said, if compliance with the proposed retrofit
requirements are applied as proposed, Sec.  121.153 would preclude this
practice for airplanes that have not been retrofitted with FRM. These
commenters argued that this result would present a burden to both U.S.
operators (who would lose the flexibility provided by Sec.  121.153)
and non-U.S. operators (for whom the value of their unmodified
airplanes would be reduced).
    Section 121.153(c) does not relate to a ``category of operation,''
such as all-cargo operations. Rather, it permits certificate holders to
operate foreign registered airplanes for any type of operation, as long
as the airplanes meet all applicable regulations. Allowing the
operation of foreign registered airplanes that do not comply with this
rule would be contrary to the intent of both Sec.  121.153(c) and this
rulemaking. It would also subject a certificate holder's passengers to
differing levels of safety based on the registry of the airplane. This
is not acceptable and we did not make the change proposed by the
commenters in the final rule. However, as discussed later in more
detail, we are working with foreign authorities to establish harmonized
flammability reduction standards. If we achieve that objective, the
``burdens'' suggested by the commenters would disappear.
10. International Aspects of Production Requirements
    The AEA and Airbus disagreed with the proposed requirement to
incorporate FRM or IMM into all new production airplanes. They stated
that existing procedures for exporting airplanes from the United States
allow the importing country to accept specific non-compliances on the
export certificate of airworthiness. The AEA also asked for
clarification of the discussion of FAA authority over airplanes
produced outside the United States. Likewise, Embraer asked that the
requirement to incorporate FRM or IMM into all new production airplanes
be dropped from the proposal. Embraer pointed out that foreign
regulatory authorities do not currently have certification standards
for FRM or IMM, so Embraer is unclear how airplanes with such systems
would be approved by the importing country. The ATA questioned the FAA
contention (by context) that the proposed rulemaking has no
international (ICAO) implications. It asked for the proposal to be
reviewed by relevant international law experts for compatibility with
the principles of sovereignty and authority in ICAO International
Standards and Recommended Practices, Annex 8 to the Convention on
International Civil Aviation, Airworthiness of Aircraft.
    As discussed in the NPRM, we intend for the proposed new production
requirements to apply to any manufacturer over which the FAA has
jurisdiction under ICAO Annex 8. For this reason, we used the same
language as Annex 8 to define the applicability of those requirements.
Under that annex (and under this rule), we have jurisdiction over
organizations to which we issue production approvals, including
production certificates. This may include organizations that accomplish
final assembly outside the United States. While no affected U.S.
production certificate holders currently accomplish final assembly
outside the United States, it is possible that they might in the
future. For example, if Boeing were to perform final assembly of a
future version of the Boeing 737 in another country, those airplanes
would still be subject to the production cut-in requirements of this
final rule as long as Boeing produces them under Boeing's U.S.
production certificate.
    Regarding the comment that current procedures allow the importing
country to accept specific non-compliances on the export certificate of
airworthiness, the commenters are referring to the waiver provisions of
Sec.  21.327(e)(4). The non-compliances referenced in that section
relate to the requirements for issuance of an export airworthiness
approval.\19\ The production cut-in requirement of this rule is
unrelated to those requirements. Rather, it requires that affected
airplanes produced under U.S. production approvals must conform to an
approved type design that meets the fuel tank flammability requirements
of this rule. Therefore, while a foreign authority may be able to waive
the requirements for issuing airworthiness approvals, it does not have
the authority under ICAO Annex 8 to override our requirements, imposed
as the State of Manufacture, for our production approval holders.
---------------------------------------------------------------------------

    \19\ For example, Sec.  21.327(e)(4) references Sec.  21.329,
which in turn references Sec.  21.183 for the requirements for a
standard U.S. airworthiness certificate. For new airplanes, Sec.
21.183 requires that the product conform to its approved type design
and is in condition for safe operation.
---------------------------------------------------------------------------

    Finally, in addition to meeting the requirements of this rule, any
airplane produced for export would also have to meet all other
requirements applicable to the production certificate holder (such as
the requirement to maintain its quality control system in accordance
with its FAA approval). These requirements cannot be waived under the
provisions of Sec.  21.327(e)(4). Therefore, we are not aware of any
basis for a foreign authority to object to our requirement for
production cut-in. Of course, once the airplane is placed into
operation by a foreign operator, the operator would have to comply with
the requirements of its authority for operation and maintenance of the
airplane, which may or may not include requirements relating to fuel
tank flammability. As discussed later in more detail, we are currently
working with foreign authorities to harmonize our requirements with
theirs.

D. Requirements for Manufacturers and Holders of Type Certificates,
Supplemental Type Certificates and Field Approvals

1. General Comments About Design Approval Holder (DAH) Requirements
    We received a number of general comments responding to the concept
of DAH requirements rather than to the DAH requirements in this
specific

[[Page 42459]]

rulemaking. We responded to these types of comments in the comment
disposition document accompanying our policy statement titled
``Safety--A Shared Responsibility--New Direction for Addressing
Airworthiness Issues for Transport Airplanes.'' Both were published in
the Federal Register on July 12, 2005 (70 FR 40168 AND 70 FR 40166,
respectively). We received similar comments on our NPRM on Enhanced
Airworthiness Program for Airplane Systems (70 FR 58508, October 6,
2005, RIN 2120-AI31). As a result, we will not respond to such comments
again here.
2. Flammability Exposure Requirements for New Airplane Designs
    As proposed, the rule requires those airplanes incorporating FRM to
limit the fleet average flammability exposure to 3 percent, and to
limit warm day exposure to 3 percent, for all normally emptied fuel
tanks located, in whole or in part, in the fuselage. All other fuel
tanks can either meet the 3 percent average flammability exposure
limitation or have a flammability exposure that is not higher than the
exposure in a conventional unheated aluminum wing tank that is cooled
by exposure to ambient temperatures during flight.
a. General Comments About Applicability to New Production Airplanes
    The NACA and its member airlines fully support the requirement for
incorporation of either an FRM or IMM to provide fuel tank inerting for
all new production airplanes, including those that already have an
approved TC or STC. Airbus, AEA, AAPA, and EASA also commented that
installation of FRM during an airplane manufacturing process may be
appropriate. The EASA expressed its support for production cut-in and
plans to amend its rules to a harmonized approach that requires
production incorporation.
    As we stated in the NPRM, ``The safety objective of these proposed
rules is to have the required modifications installed and operational
at the earliest opportunity.'' \20\ For U.S.-manufactured airplanes, we
proposed to meet this objective by requiring affected production
approval holders to incorporate these changes by the compliance date
for developing FRM or IMM service information. Recognizing that we do
not have similar authority over affected foreign manufacturers, we did
not propose a similar requirement for them. However, as noted by the
commenters, our safety objective still applies to those airplanes, and
it is equally feasible for FRM or IMM to be incorporated on new
foreign-manufactured airplanes after the necessary design changes are
developed. Further, as stated by EASA, it has agreed to harmonize
requirements for new production airplanes. Including FRM or IMM in
production is more efficient and less costly than retrofitting these
airplanes, which is also required under the NPRM.
---------------------------------------------------------------------------

    \20\ 70 FR at 70940.
---------------------------------------------------------------------------

    Based on these factors, we had assumed that FRM or IMM would be
incorporated on all airplanes produced by both domestic and foreign
manufacturers after designs were developed within two years after the
effective date of this final rule. Given the reluctance of foreign
manufacturers to commit to developing these design changes within the
prescribed period (as discussed later), we now recognize that an
operational requirement is needed to effectuate our intent.
Accordingly, operators may not operate affected airplanes produced
after September 20, 2010 unless they are equipped with FRM or IMM.
Because we had intended that all airplanes delivered after these design
changes had been developed would include these safety improvements,
this requirement is a logical outgrowth of the NPRM.
b. Flammability Analysis Using the Monte Carlo Method
    For all fuel tanks, an analysis must be performed to determine
whether the fuel tank, as originally designed, meets the fleet average
flammability exposure limits discussed above. To determine the
flammability exposure of fuel tanks, the ARAC used a specific
methodology incorporating a Monte Carlo analysis.\21\ As proposed, any
analysis of a fuel tank must be performed in accordance with this
methodology (as detailed in proposed appendix L, now appendix N, and in
the draft FAA document, Fuel Tank Flammability Assessment Method User's
Manual).\22\ We considered approving alternative methodologies in lieu
of Appendix N, but we found that no other alternative considered all
factors that influence fuel tank flammability exposure (which is the
safety objective of this rule).
---------------------------------------------------------------------------

    \21\ This methodology determines the fuel tank flammability
exposure for numerous simulated airplane flights during which
various parameters such as ambient temperature, flight length, fuel
flash point are randomly selected. The results of these simulations
are averaged together to determine the fleet average fuel tank
flammability exposure.
    \22\ As indicated in the proposed Appendix L (now Appendix N),
we are incorporating the User's Manual by reference into the final
rule. This was incorporated by reference in the final rule by
creating a new Sec.  25.5.
---------------------------------------------------------------------------

    The ATA proposed upgrading the Monte Carlo method or developing a
similar method that would be used to evaluate airplane risk of a fuel
tank explosion. The method proposed by ATA would include not only fuel
tank flammability, but also the risk of ignition sources developing in
a fuel tank based upon the specific airplane design.
    The Monte Carlo method is intended to be used to determine fuel
tank flammability alone, not the overall likelihood of a fuel tank
explosion. While the ATA's suggestion is intriguing, we do not believe
there is presently a method of accurately predicting the risk of an
ignition source developing in a fuel tank. With this final rule, we are
implementing a balanced approach to prevent fuel tank explosions: By
addressing both ignition prevention (as defined in the requirements of
Sec.  25.981(a) and SFAR 88) and flammability reduction (as defined in
this rule). Compliance with both standards ensures that fuel tank
explosion risk is acceptable.
    The EASA also expressed concerns about the proposed methodology
since it is complex and allows variations in fuel tank flammability to
be introduced by variations in the input parameters used in the
analysis. Although EASA welcomed the improvements to the Monte Carlo
method proposed in the NPRM that set the majority of the input
parameters, EASA expressed concern that the method does not adequately
address heat transfer and the assumptions retained do not allow proper
quantification of the exposure.
    We share the concern expressed by EASA that, unless properly
controlled, variation in the DAH input parameters used in the
flammability assessment could result in significant differences between
various DAHs. Fuel tank thermal modeling, including heat transfer, is
the one major variable parameter provided by the user. Appendix
N25.3(e) requires that substantiating data for the fuel tank thermal
model, along with other input parameters, be submitted with the
analysis. Therefore, we believe that Appendix N does adequately address
heat transfer and provides a method that allows for proper
quantification of flammability exposure.
    Finally, Parker Hannifin Corporation noted an error in the Monte
Carlo computer code that mistakenly added the time prior to flight and
utilized the flight time constants rather than ground time constants in
certain calculations. This error could produce two counter-

[[Page 42460]]

acting effects. In some circumstances, it could produce higher
flammability exposure when the tank-full time constant is used longer
than actually required. In other circumstances, it tends to reduce the
flammability exposure by using the tank empty-time constant earlier
than actually warranted. Overall this has the net effect of slightly
underestimating the actual fuel tank flammability exposure so
assessments using the revised computer code would produce slightly
higher flammability values. We addressed this error in the final rule
and the computer code is now correct.
c. Definition of ``Normally Emptied Tank''
    As defined in proposed Sec.  25.1803(d) (now Sec.  26.31(b)),
``normally emptied tank'' refers to a fuel tank that is emptied of fuel
during the course of a flight and, therefore, can contain a substantial
vapor space during a significant portion of the airplane operating
time. Boeing requested that the definition for ``normally emptied'' be
removed. Boeing based this request on the fact that heat input to the
tank and the heat rejection rate (i.e., the rate of heat transfer from
the tank) play more of a factor in a tank's flammability than whether
it is normally emptied.
    While we acknowledge that the heat input to the fuel tank and heat
rejection from the tank are major factors in fuel tank flammability,
the reason we are concerned about tanks that are normally emptied is
not related to their flammability. As stated in the preamble to the
NPRM, normally emptied fuel tanks can contain a substantial fuel vapor
space that could expose potential ignition sources to the fuel vapor
for an extended period of time. Fuel in tanks that are not normally
emptied covers potential ignition sources more often than fuel in
normally emptied tanks. This prevents ignition sources from igniting
fuel vapors in the tank. Therefore, normally emptied fuel tanks have a
higher likelihood of exposing flammable vapor to ignition sources than
tanks that are not normally emptied. This rule specifically
differentiates between fuel tanks that are normally emptied and other
fuel tanks by requiring reduced fuel tank flammability because of the
increased risk of an explosion in normally emptied tanks.
d. Fixed Numerical Standard
    For new airplane designs, we requested comments on whether the
reference to a conventional unheated aluminum wing tank or a fixed
numerical standard for the requirements of Sec.  25.981(b) would be
more workable and effective. The safety objective of a ``conventional
unheated aluminum wing tank'' is consistent with the ARAC
recommendation and Sec.  25.981(c) (amendment 102). However, it does
not provide a numerical standard to apply in future type certification
programs. In certain cases, the compliance demonstration would be
simplified if a fixed numerical standard were provided in the
regulation, because there would be no analysis needed to establish the
flammability exposure of a conventional unheated aluminum wing tank
that is the alternative flammability exposure. We believe this approach
has implementation advantages and should achieve the safety level
intended by the ARAC recommendation and the current approach in Sec.
25.981(c) (amendment 102).
    Transport Canada, Boeing, Airbus, and ATA agreed that including a
fixed numerical standard was preferred. Several of them suggested that
we needed to provide further justification for the selection of a 3
percent fixed value and proposed different numerical values. These
commenters did not agree with the inclusion of a variable standard of
equivalence to a conventional unheated aluminum wing tank.
    Airbus stated that a numerical value within the level recommended
by ARAC (i.e., 7 percent) would be more practical and potentially safer
than a flammability equivalency to a hypothetical wing fuel tank. While
the 3 percent limit should be considered an acceptable goal if FRM is
used, Airbus suggested that for fuel tanks that have a base
flammability exposure less than 7 percent, there should not be a
requirement to use FRM. The existing minimization of heat sources, as
required by EASA, should be adequate. Airbus concluded that
establishing a standard of 7 percent for fuel tank flammability
exposure would ensure that FRM would provide a significant benefit (at
least a 50 percent reduction in flammability) and remove the potential
to actually reduce the overall safety as a result of increased ignition
risk potential due to hazards associated with adding new FRM or IMM to
the airplanes.
    These commenters did not provide any compelling reasons to change
the proposed 3 percent average flammability exposure or to eliminate
the provision for showing equivalence to a conventional unheated
aluminum wing tank. The reason for including the fixed 3 percent
flammability exposure is to simplify the compliance demonstration. The
reason for allowing for equivalence to a conventional unheated aluminum
wing tank is to give flexibility to designers who are willing to
perform the required evaluations. The proposal from Airbus and other
commenters to increase the flammability exposure value to 7 percent
would allow a significant increase in fuel tank flammability over that
permitted by Sec.  25.981. The fleet of airplanes that ARAC determined
had achieved an acceptable level of safety was made up of airplanes
with conventional unheated aluminum wing tanks with flammability
exposures that varied from very low levels of around 1.5 percent for
outboard wing fuel tanks to the highest values below 6 percent for some
larger inboard wing tanks. These numerical values would all be lower if
calculated today, consistent with the lower values now calculated by
manufacturers for HCWTs.
    Therefore, in this final rule, we adopted a flammability standard
that includes showing a fuel tank is equivalent to a conventional
unheated aluminum wing tank or 3 percent, whichever is greater. For
purposes of this final rule, a conventional unheated aluminum wing tank
is a conventional aluminum structure, integral tank of a subsonic
transport airplane wing, with minimal heating from airplane systems or
other fuel tanks and cooled by ambient airflow during flight. Heat
sources that have the potential for significantly increasing the
flammability exposure of a fuel tank would preclude the tank from being
considered ``unheated.'' Examples of such heat sources that may have
this effect are heat exchangers, adjacent heated fuel tanks, transfer
of fuel from a warmer tank, and adjacent air conditioning equipment.
Thermal anti-ice systems and thermal anti-ice blankets typically do not
significantly increase flammability of fuel tanks.
e. Tanks Located Within the Fuselage Contour
    Boeing disagreed with the distinction in proposed Sec.  25.981
between tanks located within the fuselage contour that are normally
emptied and other tanks. Boeing suggested that main tanks and tanks not
partially within the fuselage do not represent all the tanks with low
flammability exposure and acceptable safety records. Boeing stated that
on the other hand it is possible to design a main or wing tank with
exceptional heat sources and/or minimal cooling. It is also possible to
design a normally emptied tank that is partially within the contour of
the fuselage which is low flammability (3 percent or less).
    Bombardier did not understand the justification for introducing a
maximum

[[Page 42461]]

3 percent fuel tank flammability exposure for wing tanks with a portion
of the tank located within the fuselage. Bombardier stated that there
is an inconsistency in requiring wing tanks to have flammability
exposure of between 2 percent and 5 percent, while requiring fuselage
tanks to be below 3 percent. Bombardier concluded that keeping all
tanks below a 7 percent flammability exposure level should be
considered acceptable, and recommended that tanks with less than 7
percent flammability exposure not be required to have FRM.
    The distinction in flammability exposures in the rule between tanks
located within the fuselage contour that are normally emptied and other
tanks was made because the former generally have an increased risk of
explosion. The location within the fuselage typically results in little
or no cooling of the tank and, in some cases, actually heats the tank.
Tanks that are normally emptied operate much of the time empty.
Therefore, components that could be potential ignition sources are
exposed to the tank ullage. We agree with Boeing on the possibility
that fuel tanks located in the wing can be high flammability if the
tank is heated or does not cool due to tank design features. However,
the rule limits fuel tank flammability in these tanks to 3 percent or
equivalent to a conventional unheated aluminum wing tank, addressing
that risk.
    For fuel tanks located outside the fuselage contour, Sec.  25.981,
as amended by this final rule, retains the flammability limits 3
percent or equivalent to a conventional unheated aluminum wing tank.
Only if any portion of the fuel tank is located within the fuselage
contour, and if the tank is normally emptied, is it required to meet
the 3 percent average and 3 percent warm day requirement. If an
applicant chooses to locate a portion of a main fuel tank inside the
fuselage, the rule requires that the fuel tank meet the same standard
as a main fuel tank located solely outside of the fuselage contour
(i.e., 3 percent or equivalent to a conventional unheated aluminum wing
tank wing).
    Since existing airplane types with main fuel tanks that go from the
wing into the fuselage are not normally emptied, FRM or IMM is required
for these tanks only if the tank flammability exposure exceeds 7
percent (proposed Sec.  25.1815 (now Sec.  26.33)). For future designs
using similar architecture, these types of designs would need to show
that the main tank that extends into the fuselage meets the standard of
equivalent to a conventional unheated aluminum wing tank or 3 percent.
f. Compliance Demonstration
    Boeing, Airbus, and BAE requested that applicants be allowed to use
design review to determine that an aluminum fuel tank is equivalent to
the low flammability standard fuel tank as defined by ARAC. This would
be in lieu of a detailed Monte Carlo based flammability analysis. The
BAE stated that performing a cumbersome and expensive Monte Carlo
analysis for metallic wing tanks of conventional design is unnecessary
and adds no value. For other types of tanks, or wing tanks with a
substantial heat input, BAE believes the use of alternative analytical
methods may be appropriate and suggested a qualitative assessment of
the design and the installation should be adequate to determine whether
a given tank has a low flammability exposure. Finally, BAE recommended
a simple set of objective criteria be allowed for establishing fuel
tank flammability in these tanks.
    Boeing requested that we:
     Revise proposed Sec.  25.981(b) to allow a simplified
flammability analysis for fuel tanks shown by design review to be a
Conventional Unheated Aluminum Wing Tank.
     Delete proposed Sec.  25.981(b)(1) and (b)(2), which
reference Appendixes N and M for the flammability analysis methodology
and flammability exposure criteria, respectively.
     Revise the definition of conventional unheated aluminum
wing tanks to consider allowing some minimal heat sources (i.e.,
hydraulic systems) and significant cooling which results in low
flammability exposure and a satisfactory level of safety.
    We agree with the commenters' assertion that a simplified
qualitative flammability analysis for conventional unheated aluminum
wing tanks is appropriate and have modified Appendix N to permit this.
Our intent is to limit the quantitative analysis for aluminum wing
tanks with unique or unconventional designs that are heated or designed
such that minimal cooling occurs. For example, a quantitative
flammability analysis would be necessary for a wing tank that has a
relatively small surface area, thereby minimizing surface cooling
effects, a composite tank or a tank that has equipment inducing heat
into the fuel tank greater than a small amount.
    We have also added guidance to AC 25.981-2 that describes how to
conduct a qualitative analysis to establish equivalency to a
conventional unheated aluminum wing tank. This guidance provides
examples of allowable heat sources and cooling characteristics for a
fuel tank to be considered a ``conventional unheated aluminum wing
tank,'' so that the safety standard established by the ARAC definition
for a conventional unheated aluminum wing tank is maintained. For
compliance with Sec.  25.981(d), the guidance also includes a
discussion of how Critical Design Configuration Control Limitations
(CDCCL) would need to be developed to define any critical features of
the fuel tank design needed to limit the flammability to that of a
conventional unheated aluminum wing tank.
    As for Boeing's specific changes to Sec.  25.981, we do not agree
that Sec.  25.981(b)(1) and (b)(2) should be deleted because Appendix N
provides necessary definitions and methods for establishing Fleet
Average Flammability Exposure and Appendix M establishes performance
standards for FRM. These appendices, and the references to them in
Sec.  25.981(b)(1) and (b)(2), are necessary to achieve the safety
objectives of this rulemaking. We have not adopted Boeing's suggestion
to modify the definition of ``Equivalent Conventional Unheated Aluminum
Wing.'' However, we do agree with the comment to allow some minimal
heating of tanks such as that from a hydraulic heat exchanger that does
minimal heating. We have revised the term ``Conventional Unheated
Aluminum Wing'' used in Sec.  25.981 to ``Conventional Unheated
Aluminum Wing Tank'' to clarify that the flammability of the fuel tank
is the standard. Since some minimal degree of heating typically occurs
in many of these tanks, this change recognizes that such minimal
heating is permissible.
g. Heat Sources Located in or Near Fuel Tanks
    Transport Canada and the UK Air Safety Group suggested we prohibit
the placement of heat sources within or near fuel tanks. Transport
Canada questioned why we would allow such an undesirable design
practice to continue. The UK Air Safety Group contended the NPRM failed
to address the contribution of high fuel tank temperature to fuel tank
explosions. The commenter noted that the Boeing 737 and 747 have air
conditioning units that raise the fuel tanks' temperature well above
the outside ambient temperature because these units are located beneath
the center fuel tanks.
    We agree with the commenters' underlying concern about controlling
fuel tank temperature. While locating heat sources in or near fuel
tanks increases the tanks' flammability, specifically prohibiting this
design

[[Page 42462]]

practice may not be the most efficient and effective way to address the
problem. This rule is performance-based and is seeking innovative
design solutions which could permit locating heat sources near or in
fuel tanks. For example, designers may wish to develop an FRM based
upon managing the fuel tank temperature by transferring heat between
tanks. These designs may provide flammability exposures well below that
of a tank that complied with the proposal made by the commenters. Risk
is directly proportionate to the flammability exposure of a tank.
Therefore, we have developed a flammability performance standard that
is independent of the design details of a tank installation.
h. Effects of Systems Failures on Flammability
    The CAPA requested that we ensure the effects of any system
failures that might increase the fuel tank flammability above the
acceptable limit be considered and properly evaluated prior to issuing
the final rule.
    The flammability analysis required by Sec.  25.981 includes a
requirement to show that flammability exposure does not exceed minimum
levels. It also requires that the overall flammability exposure
analysis includes consideration of system failures when demonstrating
that the FRM meets the reliability requirements of this rule. In
addition, the analysis required by Sec.  25.981(d) that determines the
CDCCL and airworthiness limitations includes consideration of possible
critical design features that must be maintained and may not be altered
to assure the flammability limits are achieved. We have provided
additional guidance and clarification in AC 25.981-2 regarding
reliability assessments and establishing CDCCL and airworthiness
limitations for FRM and IMM. Accordingly, we believe the commenter's
concerns are already addressed by the proposed language, and no change
was made to the final rule.
i. Move Flammability Exposure Method to Advisory Circular
    The EASA, Transport Canada, Boeing, and Bombardier commented that
the Monte Carlo method should not be defined in the rule as the method
for determining fuel tank flammability. Instead, it would be more
appropriately included in advisory material.
    We do not agree with these commenters. The Monte Carlo method is
specified in the rule to ensure standardization of the methodology for
determining fuel tank flammability across all airplane models so a
uniform level of safety is achieved. Advisory circulars (ACs) provide
guidance for methods, procedures, or practices that are acceptable to
us for complying with regulations. ACs are only one means of
demonstrating compliance, and we cannot require their use. Specifying
Monte Carlo analysis in an AC could result in numerous methodologies
and input parameters being used to determine flammability exposure, and
we believe that this could result in differing flammability exposures
in the fleet that may allow some fuel tanks to have greater
flammability than intended by the rule. To ensure that all DAHs reach
comparable conclusions from their assessments, it is necessary to
require that they use the same methodology. This can only be
accomplished through the rulemaking process.
    However, to accommodate minor revisions that would not appreciably
affect analytical results, we have included a provision in Appendix
N25.1(c) permitting use of alternative methods if approved by the FAA.
This is similar to the flexibility provided in Sec.  25.853 for
alternative test methods to those defined in Appendix F of part 25.
3. Flammability Exposure Requirements for Current Airplane Designs
    Proposed Sec.  25.1821 (now Sec.  26.39) contains the fuel tank
flammability safety requirements for newly produced airplanes.
Paragraph (b) sets forth the criteria that, when met by any fuel tank,
requires that fuel tank to have an FRM or IMM meeting the new
requirements of Sec.  25.981. Paragraph (c) contains the requirements
for all other fuel tanks that exceed a Fleet Average Flammability
Exposure of 7 percent.
a. Same Standards for New and Current Airplane Designs
    Boeing asked that we revise proposed Sec.  25.1821(b) to state
``any fuel tank not shown by design review to be a Conventional
Unheated Aluminum Wing Tank, must meet the requirements of Sec.  25.981
in effect on [effective date of final rule].'' In conjunction with this
change, paragraph (c) would be deleted. Boeing stated that new
production airplanes should meet the same requirements as new airplane
designs, since the criteria for tanks at risk should be a function of
heating and cooling, not whether the fuel tank is normally emptied and
located partially within the fuselage.
    We do not agree with Boeing. As discussed earlier, tanks that are
normally emptied and located at least partially within the fuselage are
generally more susceptible to explosion because of both increased
ullage and operating at higher temperatures. We have determined that
the 7 percent flammability exposure limit recommended by ARAC is an
adequate standard to determine which fuel tanks in newly produced
airplanes need an FRM or IMM. If the fleet average flammability
exposure is above 7 percent for fuel tanks normally emptied and located
within the fuselage contour, these fuel tanks will be required to be
flammable no more than 3 percent on average and 3 percent for warm day
operations. We expect that the vast majority of large transport
category airplanes will have a fleet average flammability exposure
above 7 percent for these specific fuel tanks and will be required to
comply with Sec.  25.981 for production airplanes affected by the DAH
requirement.
    Other tanks on newly produced airplanes also may not exceed the 7
percent flammability exposure limit, but the final rule would allow
reduction to that level by various methods of FRM described in AC
25.981-2 that would not necessarily require the added complexity and
cost of a nitrogen inerting based FRM. We believe this requirement is
sufficient to provide an acceptable level of safety for current
production airplanes because these tanks have significantly lower risk
of fuel tank explosions, as demonstrated by their service history.
Therefore, we do not believe the safety improvements from redesign of
these tanks to meet the new requirements of Sec.  25.981 are sufficient
to justify the resulting costs.
b. 7 Percent Exposure Flammability Questioned
    In the NPRM, we stated that fuel tanks that have a flammability
exposure higher than 7 percent are unduly dangerous. American Trans Air
commented that this statement is arbitrary, based on flawed analysis,
and cannot be supported. Bombardier expressed its opinion that the NPRM
and its supporting data did not adequately substantiate the declared 7
percent exposure. Although Bombardier considered that achieving 7
percent exposure is feasible with reasonable design precautions,
Bombardier stated that this is not an acceptable reason for creating a
standard. Bombardier also quoted information shared among the airline
industry and authorities that heated tanks may vary between 8 percent
to as high as 40 percent in flammability exposure.
    Boeing did not agree with the proposed flammability requirements
for newly produced airplanes, because fuel tanks other than those
located within

[[Page 42463]]

the fuselage contour that are normally emptied would be allowed to have
flammability of up to 7 percent. Boeing commented that this
flammability is more than twice that of what is allowed for similar
tanks in new designs. Boeing noted that the first ARAC determination
that 7 percent flammability exposure is acceptable was based on the
original coarse ARAC flammability analysis which determined that
unheated tanks had a flammability level of approximately 5 percent. Two
percent was added for potential variation resulting in the 7 percent
proposal. Boeing pointed out that the Monte Carlo analysis has been
significantly refined since the first ARAC report, and the estimated
flammability exposure of 5 percent (7 percent with potential variation)
has been reduced to be in the range of 3 percent (4 percent with
potential variation) or less for the same fuel tanks.
    We have determined that the 7 percent or less fleet average
flammability exposure recommended by ARAC is an adequate value that can
be used to identify those airplane models that need to be retrofitted
with an FRM or IMM. The fuel tank flammability limits established for
newly produced airplanes (subject to the production cut-in
requirements) are the same as those for retrofit of the existing fleet
(proposed Sec.  25.1815 (now Sec.  26.33)). We determined this
flammability exposure achieves the desired safety benefits, since
currently produced airplanes generally have conventional unheated
aluminum wing tanks, the tanks ARAC determined to have adequate safety
level, with flammability exposures below 7 percent.
    We agree with Boeing that newly produced airplanes should not be
allowed to have fuel tank flammability that is twice that of new
designs, and this is not what we intended. The intent of this rule is
to apply its safety improvements to the fuel tanks that have been shown
to have an increased risk of explosion, not to require modifications to
conventional unheated aluminum wing tanks, or other fuel tanks that
have significantly lower flammability. Data we have available for
currently produced airplanes indicate the flammability of tanks located
outside the fuselage contour have flammability below 7 percent and
further reduction in flammability exposure as recommended by Boeing
would add significant cost to the rule, since a number of fuel tanks
would be required to have an FRM or IMM to meet the suggested
flammability values of 3 to 4 percent.
    Recognizing that, based on the applicability criteria of proposed
Sec.  25.1821(a) (now Sec.  26.39), this section only applies to
current production Boeing models. We have revised paragraph (a) to
specifically identify those models. As discussed previously, we have
also added a requirement to the operational rules that operators must
meet these requirements for any airplane subject to this rule that is
produced more than two years after the effective date.
4. Continued Airworthiness and Safety Improvements
a. 7 Percent Standard Should Apply to All Tanks
    Boeing requested that Sec.  25.1815(c)(1) be modified to state
that, for fuel tanks with flammability exposure exceeding 7 percent
that require an FRM, ``a means must be provided to reduce the fuel tank
flammability exposure to meet the criteria of Appendix M of this
part.'' In addition, Boeing recommended that we delete Sec.
25.1815(c)(1)(i) and (ii). Boeing stated that any fuel tank that has
significant heat loads, regardless of the location on the airplane,
should meet the requirements of Appendix M if an FRM is selected as the
design modification.
    We do not concur with Boeing's comment that the flammability
requirements of Appendix M should apply to any fuel tank that exceeds 7
percent average flammability. As discussed previously, the reason we
are adopting more stringent requirements for fuel tanks that are
normally emptied and located within the fuselage contour is that those
tanks both have higher flammability exposure and are more likely to
have ullage exposed to ignition sources. For other fuel tanks where the
fleet average flammability exposure exceeds 7 percent, the requirements
of Appendix M apply with the exception that the flammability
requirements of M25.1(a) and (b) are replaced by the requirement that
fleet average flammability exposure must not exceed 7 percent. We
believe this is acceptable for these tanks on existing airplanes. Since
most of these tanks are not ``normally emptied,'' the risk that
flammable vapors will be exposed to ignition sources is generally much
lower.
b. Compliance Planning
    Airbus requested that the compliance planning requirements
contained in Sec.  25.1815 be removed because they are unnecessary.
Airbus believes the only important compliance date is the final date
for DAHs to submit the data and documents necessary to support operator
compliance. Airbus commented that the compliance plan requirements in
Sec. Sec.  25.1815(g), (h) and (i) add constraints on the manufacturer
with no safety benefit. Airbus stated these documents should not be
subject to a requirement with respect to the DAH documentation delivery
date. However, if the delivery dates for these documents are mandated,
Airbus requested that they be expressed in the format of a duration
tied to the date of approval of the previous submittal.
    Boeing recommended we remove the Sec.  25.1815(g)(3) requirement to
identify deviations to methods of compliance identified in FAA advisory
material, because the proposed means of compliance should not be
compared to other means. Instead, they should be evaluated on their own
merits.
    While we understand the commenters' concerns, these documents will
provide assurance that the required flammability exposure analyses and,
if applicable, proposed design changes, are being addressed in a timely
fashion. As stated in the NPRM, the resolution of fuel tank safety
issues needs to be handled in a ``uniform and expeditious'' manner.
Providing compliance times based on the dates of our previous approvals
would result in various compliance times, depending upon whether DAHs'
submissions are acceptable. It would have the undesirable effect of
providing more time for those manufacturers submitting deficient
documents.
    Compliance planning will promote communication between the affected
manufacturer and us. It will also provide sufficient time to discuss
any concerns with respect to how the affected manufacturer proposes to
analyze fleet average flammability exposure or certify design changes.
Compliance planning will also help to ensure that the affected
manufacturer is able to meet the required compliance times of the rule
for accomplishing the submittal of the flammability exposure analysis,
design changes, and service instructions, if applicable (proposed Sec.
25.1815 (now Sec.  26.33) and proposed Sec.  25.1817 (now Sec.
26.35)). We intend to closely monitor compliance status and take
appropriate action, if necessary.
    However, we do acknowledge that some provisions of proposed Sec.
25.1815(g), (h) and (i) could be removed without adversely affecting
our ability to facilitate TC holder compliance. Specifically, proposed
paragraph (g)(3) would require TC holders to identify intended means of
compliance that differ from those described in FAA advisory materials.

[[Page 42464]]

While this is still a desirable element of any compliance plan, we now
believe that an explicit requirement is unnecessary and it is not
included in the final rule. As with normal type certification planning,
we expect that TC holders will identify differences and fully discuss
them with the FAA Oversight Office early in the compliance period to
ensure that these differences will ultimately not jeopardize full and
timely compliance. Because we believe that timely review and approval
is beneficial and will save both DAH and FAA resources, the advisory
material will recommend that if the DAH proposes a compliance means
differing from that described in the advisory material, the DAH should
provide a detailed explanation of how it will demonstrate compliance
with this section. The FAA Oversight Office will evaluate these
differences on their merits, and not by comparison with FAA advisory
material.
    Similarly, proposed Sec.  25.1815(i) contains provisions that would
have authorized the FAA Oversight Office to identify deficiencies in a
compliance plan, or the TC holder's implementation of the plan, and
require specified corrective actions to remedy those deficiencies.
While we anticipate that this process will still occur in the event of
potential non-compliance, we have concluded that it is unnecessary to
adopt explicit requirements to correct deficiencies and have removed
them from the final rule. Ultimately, TC holders are responsible for
submitting compliant FRM or IMM by the date specified. This section
retains the requirements to submit a compliance plan and to implement
the approved plan. If the FAA Oversight Office determines that the TC
holder is at risk of not submitting compliant FRM or IMM by the
compliance date because of deficiencies in either the compliance plan
or the TC holder's implementation of the plan, the FAA Oversight Office
will document the deficiencies and request TC holder corrective action.
Failure to implement proper corrective action under these
circumstances, while not constituting a separate violation, will be
considered in determining appropriate enforcement action if the TC
holder ultimately fails to meet the requirements of this section.
    Finally, we realized that the rule text could more clearly state
our intent to allow DAHs flexibility to modify their approved plan if
necessary. Accordingly, we changed proposed Sec.  25.1815 (now Sec.
26.33(i)) to read: ``Each affected type certificate holder must
implement the compliance plans, or later revisions, * * *''
c. Changes to Type Certificates Affecting Flammability
    Proposed Sec.  25.1817 (now Sec.  26.35) addressed changes to TCs
that could affect fuel tank flammability. This section proposed to
require that a flammability exposure analysis be accomplished in
accordance with Appendix N for all affected fuel tanks installed under
an STC, amended TC, or field approval within 12 months after the
effective date of the final rule. An impact assessment that identifies
any features of the design change that compromise any CDCCL applicable
to any airplane with high flammability tanks for which CDCCL are
required must also be submitted to the FAA Oversight Office. This
section also proposed a requirement to develop service instructions to
correct designs that compromise airworthiness limitations, defined by
the TC holder under proposed Sec.  25.1815 (now Sec.  26.33), within 48
months after the final rule's effective date.
    Airbus proposed we restrict the application of any proposed changes
to Sec.  25.981 to new TCs and significant design changes (i.e., new
fuel tanks). For minor design changes such as relocating a fuel level
sensor or a small increase in tank capacity, the TC holder should only
be required to show no degradation in the flammability under the
criteria proposed by Sec.  25.1815. Airbus stated that the cross-
reference between what is in the preamble and Sec.  25.1815, and what
is required by Sec.  25.1817, is misleading.
    We agree with Airbus, and have revised proposed Sec.  25.1817 (now
Sec.  26.35) to require compliance with the new Sec.  25.981 only for
new fuel tanks. Other design changes that increase capacity of existing
fuel tanks must comply with Sec.  26.33. Design changes that affect the
flammability exposure of existing tanks equipped with FRM or IMM must
comply with CDCCLs for those tanks. This will ensure that these design
changes do not degrade the level of safety required by this rule.
d. Combine Sec. Sec.  25.1815 and 25.1817
    Boeing requested that we combine proposed Sec. Sec.  25.1815 and
25.1817 into one section. We do not agree with this suggestion, since
it would not achieve the goals of this rulemaking. As proposed,
Sec. Sec.  25.1815 (now Sec.  26.33) and 25.1817 (now Sec.  26.35)
would apply to different entities. Section 25.1815 (now Sec.  26.33)
would apply to TC holders of transport category airplanes, and Sec.
25.1817 (now Sec.  26.35) to auxiliary tank STC holders and future
applicants for design changes. The STC holders have distinctly
different compliance dates because information such as CDCCL developed
by the DAHs under proposed Sec.  25.1815 (now Sec.  26.33) is needed
before the STC holders can comply with proposed Sec.  25.1817 (now
Sec.  26.35). Separate sections provide a clear statement of the
requirements for each situation so affected persons can more easily
understand what is needed to comply with the rules applicable to them.
Therefore, the final rule retains the language as proposed with no
change.
e. Pending Type Certification Projects
    Proposed Sec.  25.1819 contains the requirements for pending TC
projects. As proposed, this section contains different requirements for
those transport category airplanes based on whether the application was
made before or on/after June 6, 2001 (the effective date of Amendment
25-102). Boeing requested that this section be deleted because it saw
no reason to differentiate among designs based on the date of
application.
    We partially agree with Boeing and have revised this section. In
the final rule, any pending certification projects that have not
received type certification by the effective date of this rule will be
required to meet the requirements of Sec.  25.981, as amended by this
rule. Since there are no longer any ongoing TC projects where the
application was received prior to June 6, 2001, there is no reason for
this distinction and we have removed proposed Sec.  25.1819(c).
However, we have received applications for type certification projects
after June 6, 2001, that are still pending (e.g., the Boeing 787 and
Airbus A350), and we have determined that a specific requirement in
Sec.  25.1819 is needed to address these projects. We do not believe
this section should be completely deleted, as requested, because these
projects (and future design changes to these airplanes), would not
otherwise be required to comply with Sec.  25.981, as amended by this
final rule. The change to the rule will maintain the requirement that
pending projects meet the same flammability standards as required for
new type certificates and that applicants develop CDCCL as proposed in
the NPRM.
f. Type Certificates Applied for on or After June 6, 2001
    Proposed Sec.  25.1819(d) (now Sec.  26.37(b)) requires that if an
application for type certification was made on or after June 6, 2001,
the requirements of Sec.  25.981 of this rule apply. Section 25.981
requires, in part, that the fleet average flammability exposure of a
fuel

[[Page 42465]]

tank not exceed 3 percent or that of a conventional unheated aluminum
wing tank.
    Airbus objected to the setting of a 3 percent flammability limit
for all fuel tanks for a pending type certification, if the application
was made on or after June 6, 2001. Airbus agreed that a 3 percent
flammability limit could be considered as an acceptable goal when FRM
is used. However, for fuel tanks that have a base flammability exposure
less than 7 percent, there should not be a requirement to impose FRM,
and the existing minimization of heat sources should be considered
adequate. If initial flammability is between 3 and 7 percent, the
safety benefit to reduce it to 3 percent through the use of FRM is not
justified, when considering the introduction of new failure conditions,
and operational and ownership costs of an FRM.
    Airbus apparently misunderstood the effect of the proposed
requirements of Sec.  25.1819 (now Sec.  26.37) for TCs for which
application was made on or after June 6, 2001. The following is
provided to clarify the requirements of the rule and address the
concern expressed by Airbus. The flammability requirements for an
airplane for which application was made on or after June 6, 2001, would
include Sec.  25.981 at Amendment 25-102 for all tanks except normally
emptied tanks located within the fuselage contour. As stated earlier in
this preamble, the rule text has been changed to clarify that the
flammability exposure is equivalent to a conventional unheated aluminum
wing tank or 3 percent, at the applicant's option. This flammability
exposure is unchanged from Amendment 25-102, which would not have
permitted a flammability exposure of 7 percent. This rule adds a new
requirement for fuel tanks located within the fuselage contour that are
normally emptied. Normally emptied tanks located within the fuselage
must meet the 3 percent average and the 3 percent warm day flammability
limits defined in Appendix M, which is the same flammability
requirement being applied to these types of fuel tanks on existing
airplanes.
g. Design Change to Add a Normally Emptied or Auxiliary Fuel Tank
    As proposed, Sec.  25.1819(e) would require that any future design
change to a TC for which the application is pending when this rule is
adopted and that--
     Adds an auxiliary fuel tank, or
     Adds a fuel tank designed to be normally emptied, or
     Increases fuel tank capacity, or
     May increase the flammability exposure of an existing fuel
tank must meet the requirements of Sec.  25.981, as amended by this
rule. Boeing asked that this paragraph be deleted because it is
specifically for ``pending'' type certification projects and, by
definition, there is no existing type certificate to change. If the
intent of proposed Sec.  25.1819 (now Sec.  26.37) is to define
requirements for projects in work at the time of the final rule, then
Boeing suggested there is no need for this section. Any change after
the new production compliance date would have to meet the new
production requirements (Sec.  25.1821).
    Proposed Sec.  25.1819(e) specifically targets potential future
changes to certain long-term, pending type certification programs.
Under proposed Sec.  25.1819(c), these programs would not be required
to comply with Sec.  25.981, as amended by this rule. Our intent was
that, although the original TC would not have to comply with the
current requirements, any later changes would have to comply. Since we
issued the NPRM, all of these projects have been certified, so there
are no pending projects for which this paragraph is needed. Therefore,
we have removed it from the final rule.

E. Flammability Exposure Requirements for Airplane Operators

    The proposed operating rules would prohibit the operation of
certain transport category airplanes operated under parts 91, 121, 125,
and 129 beyond specified compliance dates, unless the operator of those
airplanes has incorporated approved IMM, FRM or FIMM modifications and
associated airworthiness limitations for the affected fuel tanks. The
proposed rules would not apply to airplanes used only in all-cargo or
part 135 operations. Finally, the proposed operating rules would also
create new subparts that pertain to the support of continued
airworthiness and safety improvements.
1. General Comments About Applicability to Existing Airplanes
    Airbus, AEA and AAPA believe the retrofit requirement is not cost
effective. Our analysis showed that the benefit/cost ratio of the
production cut-in and retrofit requirements are similar. This was our
rationale for adopting the combined approach of production cut-in and
retrofit. However, these commenters believe the 7 percent discount rate
used in our cost/benefit analysis is too high and is responsible for
the determination that cost/benefit ratios are similar between the
production cut-in and retrofit. We infer from their comments that they
believe that 3 percent is a more realistic number and supports their
contention that retrofit is not justified. The commenters note that an
EASA analysis concluded that the retrofit was not justified. A major
concern was that the bulk of the retrofit costs (present value terms)
will be incurred in about 1/3 of the time (7 years) required for the
forward fit costs (22 years). They believe that the cash outlay to
retrofit in such a short time, coupled with the small safety benefit,
is not justified when compared with the cost/benefit of the production
cut-in. They also stated that the high cost of the retrofit over such a
short period would place financial stress on an industry that is
already financially constrained. In contrast, the cost of production
incorporation of FRM in new airplanes will be borne by airlines that
are prepared to accept the cost of new airplanes with the FRM included
in the ``sticker price.''
    Except as discussed previously regarding the exclusion of part 91
operations, we continue to believe that a retrofit requirement is
justified. As discussed in the NPRM and earlier in this preamble, the
risk of fuel tank explosions on the current fleet of airplanes with
high flammability tanks is still significant because, despite our
efforts to eliminate ignition sources, they continue to occur. At the
same time, we have made a number of changes to the proposed
requirements to reduce their cost and improve their cost-effectiveness.
As discussed later in this preamble, the final regulatory evaluation
(FRE) has been revised to include the benefits of preventing lost
revenue to the industry as a whole if another fuel tank explosion were
to occur. When these benefits are included, variations in the discount
rate do not alter the conclusion that this rule is reasonably cost-
effective.
    The compliance time for the retrofit requirement allows for
incorporation of design modifications over a seven-year period.
Operators can spread the costs over this time period. We have also
included a provision in the operational rules (discussed later) that
allows operators an extension of up to one year after the 50 percent
and 100 percent retrofit deadlines for full fleet incorporation of the
design modifications if the operator includes requirements in their
operations specifications to use ground conditioned air when available.
For 50 percent of an operator's fleet, this would allow retrofit to be
completed by September 21, 2015 rather than September 19, 2014.
Similarly, for 100 percent of an operator's fleet, this would allow
retrofit to be completed by

[[Page 42466]]

September 19, 2018 rather than September 19, 2017. This provision
provides a reduction in the costs to operators because it allows an
additional year to install an FRM or IMM. We also adjusted the
applicability of the rule so that older airplanes that were produced
prior to 1992, which will be nearing the end of their useful life in
passenger service, will not be subject to the phase-in-requirement of
the rule. The DAH-supported design modifications will only be required
on airplanes with significant remaining useful life in passenger
service so the benefits of the rule are optimized.
    As for the comments on the standard discount rate, the rate that is
mandated by the Office of Management and Budget when conducting
regulatory evaluations is 7 percent. The Initial Regulatory Evaluation
included a sensitivity study where variations in the discount rate
(using 3 and 7 percent) were considered. Variations in the discount
rate affect both the cost and the benefits of the rulemaking. Thus,
using a discount rate of 3 percent (as they recommend) increases the
benefits of the rulemaking, because the value of averted future
accidents would also have a higher present value.
2. Authority to Operate With an Inoperative FRM, IMM or FIMM
    In the NPRM, we requested public comment on the proposal to allow
the current Flight Operations Evaluation Board (FOEB) process to
establish the Master Minimum Equipment List (MMEL) interval for the FRM
or IMM rather than requiring a specific maximum fixed time interval
that the FRM can be inoperative. Airbus, Boeing, ATA, AEA and British
Airways supported the rule as proposed and generally agreed the FOEB is
the appropriate vehicle to establish the approved MMEL interval for
inoperative FRM. In contrast, Smith's Aero commented that FRM must be
considered a flight critical system, without MMEL relief for the
performance of the system to meet the overall intended safety level
stated by the FAA in the NPRM. Finally, Frontier asked how long an
airplane could be operated with an inoperative FRM system.
    As stated in the NPRM, the intent of the rule is to provide an
additional layer of protection from having a fuel tank explosion if an
ignition source occurs inside a fuel tank. While the FRM system is
needed to maintain the safety of a fleet of airplanes, it is not
considered flight critical for every flight, since the ignition
prevention means required by Sec.  25.981 requires robust fail-safe
features that provide an adequate level of safety during short periods
of time when the FRM is inoperative under the MMEL (no greater than 1.8
percent of the operating time). We agree with the commenters that ``FRM
designers'' should make the design goals for the MMEL relief intervals
available and notify the FOEB of their recommendation. The allowable
MMEL interval is design dependent and cannot be defined by us until a
design is presented and the interval is justified by the system
reliability analysis and the FOEB.
    Frontier also asked whether en route weather conditions would be a
factor with the MEL. At this time, en route weather conditions are not
part of the consideration for operation under the operator's MEL. This
is one of the considerations in the Monte Carlo assessment, so
operation under an operator's MEL during warm days would not be an
additional consideration for the MMEL.
3. Availability of Spare Parts
    Frontier asked if we had given proper consideration to the fact
that there will most likely be an initial spare parts shortage. The
compliance time for fleet-wide retrofit of FRM or IMM is nine years
after the effective date of this final rule, with 50 percent compliance
required within 6 years. Therefore, the manufacturers of components
should have the capability to produce needed spares and no shortage of
parts is anticipated. We have not included a consideration of parts
shortages when establishing the MMEL interval.
4. Requirement That Center Fuel Tank Be Inert Before First Flight of
the Day
    Frontier requested information on whether the final rule would
require that the center fuel tank be inert before the first flight of
the day and, if so, if the Auxiliary Power Unit is inoperative, could
the inerting system then be inoperative until after main engine start.
The final rule does not directly address the operational details of the
FRM. These will be determined based on the DAH's design and any
operating limitations that may be necessary to meet the performance
standards of this final rule.

F. Appendix M--FRM Specifications

    Appendix M to part 25 contains detailed specifications for all FRMs
if they are used to meet the flammability exposure limitations. These
specifications are designed to ensure the performance and reliability
of FRMs. We received several comments on Appendix M and have made
changes to the rule based on some of them.
1. Fleet Average Flammability Exposure Level
    Paragraph M25.1(a) requires that the Fleet Average Flammability
Exposure of each fuel tank may not exceed 3 percent of the Flammability
Exposure Evaluation Time. As discussed previously, as a portion of this
3 percent, if flammability reduction means (FRM) are used, each of the
following time periods cannot exceed 1.8 percent of the FEET: (1) When
any FRM is operational but the fuel tank is not inert and the tank is
flammable; and (2) when any FRM is inoperative and the tank is
flammable. Boeing requested a change to this paragraph to clarify that,
for both the operational and inoperative requirements, only time
periods when the fuel tank is in a flammable state are counted toward
each 1.8 percent flammability exposure limit.
    We agree that the method of determining these times needs
clarification and we have revised paragraph M25.1(a) as requested by
Boeing.
2. Inclusion of Ground and Takeoff/Climb Phases of Flight
    Paragraph M25.1(b) requires that ground, takeoff and climb phases
of flight be included in the fuel tank fleet average flammability
exposure analysis. Boeing asked that paragraph M25.1(b) be reworded to
exclude a specific reference to the takeoff flight phase. Boeing's
justification was that there is no benefit in conducting a separate
flammability analysis for the takeoff phase of flight since it is a
very short duration. Boeing recommended the takeoff phase be included
with the climb phase of flight. Boeing also suggested the rule clarify
that the transition from ground to climb phase for this analysis occurs
at weight off wheels.
    We agree with Boeing and have revised paragraph M25.1(b) in the
final rule to remove consideration of the takeoff phase of flight as a
separate requirement. These two phases are now required to be
considered in combination using the term ``takeoff/climb'' phase. In
addition, we added a sentence to paragraph M25.1(b)(2) stating that the
transition from ground to takeoff/climb phase for this analysis occurs
at weight off wheels.
3. Clarification of Sea Level Ground Ambient Temperature
    Paragraph M25.1(b)(1) requires that the fuel tank fleet average
flammability

[[Page 42467]]

exposure analysis, as defined in Appendix N, ``must use the subset of
flights starting with a sea level ground ambient temperature of
80[deg]F. (standard day plus 21[deg]F. atmosphere) or more, from the
flammability exposure analysis done for overall performance.'' An
individual commenter requested that we define the term ``more'' in this
statement. We agree that this requirement needs clarification and, in
the final rule, paragraph M25.1(b)(1), we replaced the word ``more''
with the word ``above.'' We also replaced the word ``starting'' with
``that begin.''
4. Deletion of Proposed Paragraph M25.2 (Showing Compliance)
    Paragraph M25.2 establishes the means for showing compliance with
fuel tank flammability requirements. Boeing requested the contents of
paragraph M25.2 be moved to Advisory Circular 25.981-2A as it defines a
method of compliance and, as such, should be located in an AC.
    As discussed previously, ACs provide guidance for methods,
procedures, or practices that are acceptable to us for complying with
regulations. ACs are only one means of demonstrating compliance, and we
cannot require their use. The compliance means in paragraph M25.2 is
regulatory in nature to ensure that applicants are providing the data
necessary to validate the parameters used in their calculations for
fuel tank fleet average flammability exposure (as required by paragraph
M25.1), and to substantiate that their system meets these requirements
during normal airplane operations for any combination of airplane
configuration (as required by paragraph M25.2(b)). We have made no
change as a result of this comment.
5. Deletion of ``Fuel Type'' From List of Requirements in Proposed
Paragraph M25.2(b)
    Boeing also requested that paragraph M25.2(b) be revised to remove
``fuel type'' from the list of requirements and add ``or other relevant
airplane system configuration'' to it. Boeing stated the items listed
in paragraph M25.2(b) affect the performance of a FRM system that is
supplied by engine bleed air, and fuel type does not affect bleed
system pressure. We agree with Boeing and have revised this paragraph
in the final rule.
6. Latent Failures
    Paragraph M25.3(a) requires that reliability indications be
provided to identify latent failures of the FRM. These indications are
needed to ensure appropriate actions can be taken to maintain the FRM's
reliability. An individual commenter asked that we define what is meant
by ``reliability indications'' in paragraph M25.3.
    In this context, reliability indications are normally computer
messages or lights that identify whether components are functioning
properly. Reliability indications are likely to be needed for the FRM
to meet the reliability requirements in the rule. The type of
indications needed will depend on the design and the outcome of the
reliability analysis. If a nitrogen inerting FRM were to be developed
with no indication of system failures, the system would have
significant exposure to long-term operation with latent failures.
Maintenance indications would likely be needed so that the minimum
reliability of the system could meet the rule.
    Boeing requested that paragraph M25.3 be deleted or modified to
remove the term ``latent.'' This would be consistent with the special
conditions issued for the Boeing 737 and 747 flammability reduction
systems. In addition, the term ``latent'' would not be applicable if an
indication is provided. An individual commenter agreed, stating that
latent failures are not detectable and, hence, cannot be indicated.
Embraer commented that both paragraphs M25.3(a) and (b) should be
deleted because a literal interpretation would require any latent
failure to be detected and indicated. This contradicts the NPRM's
preamble, which states that the designer is allowed to make a trade-off
between system failure probability and failure detection/ annunciation
to show compliance with the system performance requirements. In
addition, Embraer maintained that paragraph M25.3(a) is already
addressed and should not be repeated here because the requirement for
failure detection is inherent in the flammability exposure requirement
and in the 1.8 percent limit on system failure contribution to
flammability exposure.
    On a related topic, Airbus and Embraer commented that the proposed
rule is too restrictive and mandates an excessive amount of indication
and monitoring. Airbus indicated that the proposed text appears to
assume the adoption of an active system to reduce flammability and this
may not necessarily be appropriate if a passive system were to be used.
Some means of verifying that the passive means is fully functional
could be required, but it may be inherent in the design and therefore,
no specific action would be required except to ensure that other
airplane modifications do not adversely affect the fuel tank
flammability.
    The FAA agrees with these commenters and has modified paragraph
M25.3(a) in the final rule.
    This change makes it clear that the intent of the rule is to
require only those indications needed to assure any FRM meets the
minimum reliability requirements of the rule. The preamble to the NPRM
provided a detailed explanation of the intent of these requirements.
The need for indications is determined from the system reliability
assessment that requires a minimum reliability for any FRM. The type of
indications that may be needed to meet the reliability requirements
depends upon the details of the design and the outcome of the system
reliability analysis. Various design methods may be used to make sure
an FRM meets the reliability and performance requirements in this rule.
For example, if an FRM based upon nitrogen inerting is developed and no
indication of system failures is provided, the system would have
significant exposure to long-term operation with latent failures.
Maintenance indications would likely be needed so that the minimum
reliability of the system could meet the rule. Other designs may use
active or passive cooling means for flammability reduction. For these
systems, the level of indication required would depend upon the
reliability of the cooling system components.
    The need for FRM indications and the frequency of checking system
performance (maintenance intervals) must be determined based on the
results of the FRM fuel tank fleet average flammability exposure
analysis. The determination of a proper maintenance interval and
procedure will follow completion of the certification testing and the
reliability analysis used to establish the system complies with the
performance requirements.
7. Identification of Airworthiness Limitations
    Paragraph M25.4(a) requires that if FRM is used to comply with
paragraph M25.1, airworthiness limitations must be identified for all
maintenance or inspection tasks required to identify failures of
components within the FRM that are needed to meet paragraph M25.1.
Boeing requested that paragraph M25.4(a) be modified to require only
airworthiness limitations be identified for ``significant'' maintenance
or inspection tasks. Boeing stated that it is overly restrictive to
require that all maintenance tasks be identified as airworthiness
limitations. It argued that applicants should be granted the
flexibility to identify significant tasks as

[[Page 42468]]

airworthiness limitations and other non-significant tasks as
maintenance significant items.
    We agree with Boeing that we should not require that all
maintenance tasks for FRM be identified as airworthiness limitations.
Airworthiness limitations for the FRM system are only required for
those FRM components that, in the event of failure, would affect the
ability of the fuel tank to meet the Fleet Average Flammability
Exposure specified in paragraph M25.1. We regard any task that is
necessary to meet this objective as ``significant.'' We recognize that
manufacturers are also required to provide other maintenance
information for the FRM as part of the instructions for continued
airworthiness required by Sec.  25.1529.
8. Catastrophic Failure Modes
    EASA noted that Appendix M significantly differs from the
harmonized special conditions it used for certifying FRM on some
specific airplane models. EASA asked that we explicitly state that
catastrophic results must not occur from any single failure or
combination of failures not shown to be extremely improbable (for the
FRM system) as required in the noted special conditions. We agree that
possible catastrophic failure modes of the FRM must be shown to meet
the requested standard. However, we do not agree that EASA's change is
needed since the regulatory intent is already addressed by other
regulations that apply to FRM. For example, the general requirements of
Sec.  25.901 that apply to all Subpart E regulations apply to an FRM
certificated to meet Sec.  25.981 and Appendix M. Therefore, we did not
make any change to Appendix M based on EASA's comment.
9. Reliability Reporting
    Paragraph M25.5 requires the applicant to demonstrate an effective
means to ensure collection of FRM reliability data and to provide a
report to the FAA. We requested comments on the proposal to require
DAHs to submit a quarterly report on FRM reliability for 5 years. We
consider these reports necessary to determine whether the predicted
reliability for these systems is accurate, and to enable us to initiate
necessary corrective actions if they are not. We intend for DAHs to
gather the needed data from operators using existing reporting systems
that are currently used for airplane maintenance, reliability, and
warranty claims. The operators would provide this information through
existing or new business arrangements between the DAHs and the
operators.
    The AEA and ATA questioned this reliability reporting process. They
stated the current reporting systems may not be equipped to accommodate
this new data requirement without additional burden and cost. Airbus
also stated the reporting requirement is unclear and without sufficient
detail to enable them to fully comment. The AEA and Airbus also contend
that the reporting requirement places operators in a position of having
an obligation to report this information to the DAHs where such an
obligation did not previously exist. They suggested that we not rely on
technicalities and recognize the new obligation being imposed on the
operators. Finally, Transport Canada commented that the rule appears to
require extensive data collecting and reporting and requested more
details be provided regarding what this data will be used for.
    The purpose of collecting reliability data is to ensure that
failures of the system are reviewed and corrected. In this manner,
system reliability is enhanced and FRM malfunctions will become very
infrequent. The reporting requirement will also provide data necessary
to validate that the reliability of the FRM achieved in service meets
the values used in the fleet average flammability exposure and
reliability analyses so that the actual flammability reduction in
service airplanes will achieve the safety goals of this rulemaking.
    The reliability reporting requirements in paragraph M25.5 would not
add an additional burden or cost to the operators. We also continue to
believe that this rule does not directly impose reporting requirements
on operators. These reporting requirements are placed upon the DAH, not
the operator. The NPRM and proposed AC 25.981-2B provided a description
of the level of complexity that was intended in the quarterly reporting
requirements. Furthermore, they do not specify that a new reporting
system be created. The current reporting system could be used to gather
the data and it could then be provided to the DAHs through normal
business agreements. The DAH is required to make arrangements to
collect sufficient data and provide a report to us. Reporting would be
necessary only for a representative sampling of airplanes, as
determined by the manufacturer in its compliance plan. Airlines
routinely collect and store reliability data from airplane systems for
a variety of reasons, such as engine and airplane system reliability
data collected for Extended Twin Operations, warranty claims and
maintenance planning, and in many cases they report these data to DAHs.
    Therefore, DAHs should be able to readily obtain these data through
normal business practices. As a practical matter, DAHs will be
monitoring the performance of these systems, just as they monitor other
systems, both for warranty and liability reasons. Operators will be
providing this information to DAHs as normal business practice to
obtain DAH support in correcting any problems that occur. Our
expectation is that the DAHs' compliance plans will simply state that
DAHs will compile this information into periodic reports (which they
would normally do for their own use anyway) and provide them to the
FAA. No change has been made to the final rule as a result of these
comments.
    Bombardier requested that paragraph M25.5(b) be revised to allow
non-U.S. manufacturers to submit their reports to their national
authorities rather than the FAA. While we acknowledge that submitting a
report to a foreign manufacturer's national authority might simplify
the paperwork exchange, at this time other authorities have not agreed
to harmonize with this rule. Therefore, there are no corresponding
regulations that would require the submittal of reliability reports to
these authorities or to ensure that we will see these reports. We have
revised the requirement to allow for FAA approval of alternative
reporting procedures, which would include reporting to other
authorities with harmonized requirements. The rule also provides that,
after the first five years of reporting, if the demonstrated
reliability of the FRM meets and will continue to meet the reliability
requirements in paragraph M25.1 (not to exceed 1.8 percent of the
FEET), other reliability tracking methods could be proposed to us for
approval, or possibly reporting could be eliminated.
    Boeing requested that M25.5(b) be revised to allow the applicant to
suggest alternative methods of reporting and submit the report to us on
a yearly basis instead of a quarterly basis. It asserted that a one-
year reporting requirement will allow for more statistically
significant data to be collected for new systems. We agree that a
quarterly requirement may be unduly burdensome, but we believe that a
yearly requirement is too long to enable us to initiate timely
corrective action to address reliability problems. Therefore, we have
modified paragraph M25.5(b) in the final rule to extend the reporting
to once every 6 months for the first five years after service
introduction of the FRM. This reporting period should

[[Page 42469]]

allow adequate time to gather data to establish the performance of the
FRM and for any needed corrective actions to be taken if the
performance of the FRM falls below minimum levels.
    Boeing also requested changes be made to allow applicants that have
established reporting methods to suggest these as alternative methods
of meeting the reporting requirements. We believe the current wording
allows the DAH the latitude to develop a reporting system and request
FAA approval based upon their business arrangements with operators so
long as the reporting system provides sufficient data to the FAA to
determine the reliability of the FRM. Allowing the use of alternative
reporting methods could lead to disparate reports among manufacturers,
making FAA oversight difficult.

G. Appendix N--Fuel Tank Flammability Exposure and Reliability Analysis

1. General
    Appendix N to part 25 provides the requirements for conducting the
analyses for fleet average fuel tank flammability exposure required to
meet Sec.  25.981(b) and Appendix M and to comply with part 26
requirements. Appendix N contains the method for calculating overall
and warm day fuel tank flammability exposure values needed to show that
the affected airplane's tanks comply with the proposed limitations on
flammability exposure.
2. Definitions
    Paragraph N25.2 provides specific definitions associated with
flammability and analysis terminology used in Appendix N. We received
comments requesting clarification on five of these definitions:
    a. Ullage: Boeing suggested this definition should ensure that all
of the ullage space is considered (not just the fuel volume), and we
agree. In the final rule, this definition has been revised to clarify
that the total ullage space must be considered.
    b. Flammability Exposure Evaluation Time (FEET): An individual
commenter wanted to understand when the evaluation time begins and ends
for airplanes using ground conditioned air with the auxiliary power
unit (APU)/ground power unit (GPU) operating or electrical power that
is connected to the airplane. The evaluation time would begin as soon
as the airplane is prepared for flight, regardless of whether an APU or
electrical ground power is used. The time would end as soon as the
airplane has landed and passengers and crew have disembarked and
payload has been unloaded. In passenger operations where numerous
flights may occur each day, this definition would result in all the
time between flights also being part of the FEET. The only exception
would be the time at the end of the last flight of the day to the point
in the next morning when the airplane is being readied for flight. This
is consistent with the definition for FEET given in paragraph N25.2(b).
    c. Bulk Average Fuel Temperature: An individual commenter suggested
the definition include the means for determining ``bulk average fuel
temperature.'' As we stated in the preamble to the NPRM, the
determination of whether the ullage in the fuel tank is flammable is
based on the temperature of the fuel in the tank or compartment of
interest. This is derived from a fuel tank thermal model, the
atmospheric pressure in the tank, and the properties of the fuel. The
thermal model is comprised of temperature data acquired from various
locations within the fuel tank. In order to express the fuel
temperature of the tank as a whole in the fuel tank fleet flammability
exposure analysis, a weighted average by volume should be calculated at
each point in time since the temperature may vary across the tank or
compartments of the tank depending upon the volume of that area. We
will provide additional guidance on how to determine Bulk Average Fuel
Temperature in AC 25.981-2A.
    d. Flash Point: An individual commenter asked what the term
``heated sample'' meant in this definition. The standardized methods
for determining flash point are ASTM D 56 and ASTM 3828. Both methods
place a sample of fuel in a closed cup and heat it at a constant rate.
A small flame is introduced into the cup, and the lowest temperature at
which ignition is observed is referred to as the flash point. The
heated sample is the fuel that is placed in the closed cup when
conducting this test.
    e. Inerting: An individual commenter requested that fuel removal
from the ullage mixture be included as an acceptable inerting method.
We do not agree with this request. The definition of inerting is based
upon oxygen concentration, not fuel content of the ullage. The Monte
Carlo method uses the bulk fuel temperature to determine fuel tank
flammability, and does not consider transport effects or tank
ventilation. However, if an applicant wishes to consider methods for
removing fuel from the ullage mixture, it could request a finding of
equivalent safety under the provisions of Sec.  21.21. To be
equivalent, such a method would have to be shown to provide at least
the same level of safety as an FRM meeting the performance requirements
of Appendix M.
3. Input Parameters
    Paragraph N25.3(c) provides the parameters that are specific to a
particular airplane model under evaluation that must be provided as
inputs to the Monte Carlo analysis. Boeing had two comments on these
parameters.
    First, Boeing requested we add a new parameter to paragraph
N25.3(c) for airplane utilization. This parameter would require the
applicant to provide data supporting the number of flights per day and
the number of hours per flight from existing fleet data. Boeing stated
that this information is necessary to determine when to apply the
diurnal effect that is required by paragraph N25.4(c) based upon the
number of flights per day. The number of hours per flight will also
provide validation of the mean hours per flight generated by the Monte
Carlo analysis.
    We agree with Boeing's comment and the final rule includes a new
paragraph N25.3(c)(7) for airplane utilization that addresses this
comment. Boeing's second comment was a request that the statement ``or
for the section of the tank having the highest flammability exposure''
be removed from paragraph N25.3(c)(5). As proposed, paragraph
N25.3(c)(5) requires that, for any fuel tank that is subdivided by
baffles or compartments, the bulk average fuel temperature inputs must
be provided either for each section of the tank or for the section of
the tank having the highest flammability exposure. Boeing stated that
every region in a fuel tank should be considered in order to establish
the total flammability exposure of the tank. If the bulk temperature
input only consisted of a section of the fuel tank having the highest
flammability exposure, Boeing argued that the total flammability of the
tank would not be accurately accounted for because the analysis would
not consider regions that were less flammable.
    Any fuel tank that is compartmentalized or subdivided into sections
by baffles is ``flammable'' under the definition for Appendix N
(N25.2(c)) when the bulk average fuel temperature within any section of
the tank that is not inert is within the flammable range for the fuel
type being used. We agree with Boeing that the clause ``or for the
section for the tank having the highest flammability exposure'' in
paragraph N25(c)(3) causes confusion, and we

[[Page 42470]]

have revised paragraph N25.3(c)(5) as requested.
    We are providing guidance in AC 25.981-2 on the need to conduct the
flammability analysis for each bay or compartment and then sum the time
any portion of the tank is flammable in the flammability analysis.
4. Verification of ``Flash Point Temperature''
    An individual commenter requested verification of the flash point
temperature (120 [deg]F) that is used in Table 1 of Appendix N. We have
defined in Table 1 of Appendix N a ``mean fuel flash point
temperature'' based upon worldwide survey data that was collected from
1998 through 1999. The Monte Carlo analysis varies the flash point
based upon the distribution of possible flash point temperatures for
the fuel, similar to what would be expected for a fleet of airplanes
where fuels from various refineries and locations are used.

H. Critical Design Configuration Control Limitations (CDCCLs)

    Past experience has shown that critical features of airplane
designs have inadvertently been changed when maintenance actions or
alterations to airplanes have been made. For example, critical wiring
that was intended to be separated from other wiring to prevent possible
unsafe conditions has been modified so new or rerouted wiring was co-
routed with the critical wires. These instances revealed the need for
airplane designers to identify safety critical features, in this case
wiring separations, and for these features to be marked so that
maintenance personnel are aware of the critical features.
    We proposed adding fuel tank flammability related design features
to the existing fuel tank ignition source CDCCL requirements in Sec.
25.981(d) (formerly paragraph (b)). This section requires CDCCL,
inspections, or other procedures as necessary, to prevent increasing
the flammability exposure of tanks above that permitted by the amended
Sec.  25.981(b) and to prevent degradation of the performance and
reliability of any means provided for compliance with paragraphs
25.981(a), (b) or (c). We also proposed adding fuel tank flammability
to the existing requirements to place visible means of identifying
critical features of the design in areas of the airplane where
foreseeable maintenance actions, repairs or alterations could
compromise the CDCCL. Similar provisions were proposed in Sec.
25.1815(e) for existing type certificates.
1. Remove Requirement
    Boeing, Embraer and Bombardier requested that we remove the
requirement to establish CDCCLs to prevent the increase of flammability
in the fuel tanks and to prevent degradation of the performance and
reliability of the FRM. They stated that it is not practical or
effective to try to control flammability through the use of CDCCLs.
Instead, they argued that the certification process should be used to
establish the design's flammability exposure. Bombardier also pointed
out that the type certification data sheet is the appropriate means to
capture limitations (e.g., fuel type, fuel temperature) that would
affect flammability.
    The intent of the CDCCL requirement is to define the critical
features of the design that could be unintentionally altered in a way
that could cause a reduction in fuel tank safety. In the case of IMM or
FRM, maintenance or alterations to the airplane could significantly
affect fuel tank flammability and the performance of these systems.
Since the heating or cooling rate of a fuel tank could be a critical
feature, placing a heat exchanger or other heat source in or near the
tank or changing the cooling rate by transferring warm fuel to the tank
are examples of changes that could result in a significant increase in
fuel tank flammability.
    The commenters did not provide any substantiating information as to
why they believe it is not practical or effective to use CDCCLs to
control fuel tank flammability. Our experience with applying the CDCCL
concept to fuel tank ignition sources has shown it to be both practical
and effective. Locating this information on the TC data sheet, as
suggested by Bombardier, would not provide the information to
individuals, such as maintenance personnel, who could be responsible
for inadvertently changing the system. Accordingly, we do not believe
this suggestion would be effective. In contrast, as airworthiness
limitations, CDCCLs are clearly defined as maintenance requirements
that are routinely complied with by maintenance personnel and that are
enforceable under the operational rules (e.g., Sec.  91.403(c)). The
intent of applying the CDCCL concept to FRM and IMM is to provide a
common location within the maintenance instructions where information
on fuel tank safety related critical features are located. Therefore,
we have retained the requirement in Sec.  25.981(d) to identify CDCCLs
for FRM and IMM.
    On a related issue, paragraph (h) of each of the proposed
operational rules would have required operators to comply with the
CDCCLs. In the NPRM, we inadvertently omitted reference to Sec.  25.981
as one of the sources of requirements for these CDCCLs. Therefore, we
have added these references to the final rule. This change is simply
clarifying, since operators are required to comply with airworthiness
limitations under existing regulations.
2. Clarification on Responsibility for Later Modifications
    As proposed, Sec.  25.1817(d) (now Sec.  26.35(d)) would require
that modifications made to an airplane comply with any CDCCL applicable
to that airplane. The AEA questioned whether this paragraph would
require the TC holder or STC applicant applying for a design change to
achieve a flammability exposure level equal to or better than that
existing on the unmodified airplanes, or if the TC holder or STC
applicant will be held to the flammability exposure limits specified in
the rule.
    The proposed requirement for TC holders to develop CDCCL is
contained in proposed Sec.  25.1815(e) (now Sec.  26.33(d)). It would
require CDCCL ``to prevent increasing the flammability exposure of the
tanks above that permitted under this section and to prevent
degradation of the performance of any means provided under paragraph
(c)(1) or (c)(2) \23\ of this section.'' The AEA has identified an
ambiguity and potential conflict in this quoted provision.
Specifically, if a TC holder develops FRM whose performance exceeds
that required by proposed Sec.  25.1815(c)(1), it is not clear whether
the CDCCL would have to maintain the flammability exposure provided by
the FRM or whether the rule would allow an increase in flammability
exposure up to that permitted (i.e., 3 percent or equivalent to a
conventional unheated aluminum wing tank, along with the ``warm day''
requirement).
---------------------------------------------------------------------------

    \23\ Paragraphs (c)(1) and (c)(2) provide for FRM and IMM,
respectively.
---------------------------------------------------------------------------

    To eliminate this ambiguity, we have deleted the reference to
paragraph (c)(1) in the quoted provision. This revision has the effect
of requiring CDCCL for FRM that allow increasing flammability up to
that permitted by the rule, but retains the requirement that
degradation of performance of IMM is not permitted. Since IMM may be
installed on high flammability tanks, degradation of IMM could have
serious safety consequences and would not be consistent with the intent
of the rule.

[[Page 42471]]

    We note that TC holders may be inclined to develop overly stringent
CDCCL for FRM that could potentially make it impossible for holders of
auxiliary fuel tank STCs to meet them. This would force operators to
deactivate these tanks. This over-stringency would not be consistent
with this rule's intent, which is to minimize the burden on operators,
consistent with achieving the safety objectives of this rule. This
issue is discussed in more detail in AC 25.981-2B.
    Proposed Sec.  25.981(d) contained the same ambiguity by requiring
CDCCL to prevent degradation of performance and reliability of any
means provided according to paragraph (b) of that section (FRM). We
have made a similar change to paragraph (d) to allow degradation of FRM
as long as the airplane still meets the standard required by paragraph
(b).
3. Limit CDCCLs to Fuel Tanks That Require FRM or IMM
    Boeing requested that proposed Sec.  25.1815(e) (now Sec.
26.33(e)) be modified to only require CDCCLs that are necessary to
prevent the increase of fuel tank flammability for fuel tanks that
require an FRM or IMM. Boeing stated that development of CDCCLs for
other fuel tanks is not practical, nor is there history to show that
changes to the fuel tanks of airplanes in service significantly
increase flammability in the tanks. Boeing also requested that the
requirement to make critical features of the design visibly
identifiable only apply to areas where it is practical to do so.
    For existing designs subject to proposed Sec.  25.1815(e) (now
Sec.  26.33(e)), we agree with Boeing, and have limited the
applicability of the requirement to develop CDCCL to those tanks for
which FRM or IMM are required. We recognize that there are many
existing modifications that may affect the flammability exposure of
existing fuel tanks. We agree with Boeing that, for main tanks and
other tanks not incorporating FRM or IMM, it is impractical to impose
CDCCLs on these tanks that may result in significant compliance
problems for affected operators. For tanks equipped with FRM or IMM,
however, we believe CDCCLs are necessary to prevent degradation of
these systems below acceptable levels of performance.
    We also agree with Boeing that, in many instances, it may not
always be practical to mark critical features relating to controlling
fuel tank flammability and the proposed rule should be modified to
allow the applicant to justify why markings are not needed. We have
modified the next to last sentence in Sec.  26.33(e) accordingly.
    This change will allow acceptance of designs without markings when
the applicant can show that such markings would be impracticable. We
intend for applicants to identify any CDCCL that are required and to
provide justification for why the marking would be impracticable. Like
all CDCCLs, these would still be documented as airworthiness
limitations in the instructions for continued airworthiness.
4. STC Holders May Not Have Data to Comply
    The AEA and Airbus challenged our statement in the NPRM that
operators have access to information that may be needed by STC and
field approval holders to perform flammability and impact assessments.
The commenters noted that such information is highly proprietary and is
rarely provided to operators. AEA added that contractual agreements to
obtain TC holder information are difficult, if not impossible, to
obtain.
    For many years, the FAA and other regulatory authorities (including
EASA) have routinely required manufacturers to make available
information that they consider proprietary when we determine providing
this information is necessary for aviation safety. For example, most
ADs reference information that would otherwise be proprietary in the
form of service bulletins, which manufacturers are required to make
available to operators. Similarly, Sec.  21.50 requires manufacturers
to make available instructions for continued airworthiness, which
manufacturers would also typically consider proprietary.
    In existing Sec.  25.981(b), we required DAHs to define and make
available CDCCL to prevent the unintended creation of ignition sources
as a result of maintenance or airplane modifications. In proposed Sec.
25.981(e), we required the identification of critical features of a
design that cannot be altered without consideration of the effects on
safety. As discussed previously in this section, the final rule
includes a new requirement for CDCCLs affecting fuel tank flammability.
    Some of the data that STC and field approval holders may need are
already normally provided to operators in the airplane flight manual,
including fuel management information and airplane climb rates. For
other necessary data, such as fuel tank thermal characteristics, we
believe that the market will promote business agreements where TC
holders will make their data available to customers willing to pay for
the data. Airbus or other TC holders may make a business decision not
to support their customers and provide these data. In these cases, it
may be necessary for the operator or STC applicant to acquire the data
from other sources. Another option is for applicants to provide a Monte
Carlo analysis based on conservative inputs for parameters where no
data are available. For example, an applicant could provide thermal
characteristics data that are conservative so that detailed testing and
confirmation of data from flight testing of an airplane would not be
required. Finally, if these approaches are not practical, the
information needed to conduct the Monte Carlo analysis could be
obtained from in-service airplanes.\24\
---------------------------------------------------------------------------

    \24\ Most of the STCs that could be affected by this rulemaking
are auxiliary fuel tanks that use pressurized air to transfer fuel.
In these cases, the inputs needed for the Monte Carlo assessment are
simplified because the fuel tank pressure is controlled to provide
fuel transfer, and the temperature changes of the fuel tank are
limited because the fuel tank is located in the cargo compartment.
---------------------------------------------------------------------------

I. Methods of Mitigating the Likelihood of a Fuel Tank Explosion

1. Alternatives to Inerting
    In the IRE, we selected the use of onboard nitrogen inerting to
assess the costs of reducing fuel tank flammability. By doing this,
several commenters thought we were mandating fuel tank inerting as the
only acceptable means of compliance. ATA and Bombardier commented that
the proposal is not a performance-based rule, since it ``effectively
prescribes the use of fuel tank inerting.'' ATA also stated that they
were not aware of any existing or emerging FRM or IMM that would meet
the proposed performance-based requirements other than inerting.
Frontier Airlines questioned why we focused on FRM and IMM as methods
of compliance when the FAA concluded that other solutions were better
and more practical.
    This rule does not mandate fuel tank inerting as the only
acceptable means of compliance. Rather, it establishes performance-
based requirements that allow applicants to choose the FRM or IMM that
best suits their particular airplane design, so long as it meets the
performance requirements of this final rule. While the Initial
Regulatory Evaluation is based upon the use of inerting, this
technology was chosen because it is considered the most cost-

[[Page 42472]]

effective based upon extensive review by industry experts on the ARAC.
    Technology now provides a variety of commercially feasible methods
to accomplish the vital safety objectives addressed by this rule.
Advisory Circular 25.981-2 discusses a number of technologies other
than fuel tank inerting that can be used for demonstrating compliance.
For example, many auxiliary tank manufacturers are considering
pressurizing the fuel tanks to reduce flammability, and many military
airplanes use IMM consisting of polyurethane foam. One recent applicant
has proposed FRM incorporating pressurization of the fuel tanks and a
fuel recirculation system that circulates fuel to the outboard wing to
cool the fuel. Therefore, we believe that other technologies are
available.
    ATA commented that we should consider convening an industry study
group to re-examine the potential of higher flash point fuel as a
possible alternative method for reducing flammability and overall
airplane level risk. ATA noted that refineries may now be capable of
producing higher flash point fuels in the near term in sufficient
quantity for commercial aviation use. In addition, Boeing advised ATA
that a 10 [deg]F elevation in the flash point standard for Jet A could
effect a reduction in flammability exposure rates approximately
equivalent to the proposed FRM. While ATA acknowledged the likelihood
is not high that this approach would provide a more cost-effective
solution than FRM, particularly in the long term, it deserves
reconsideration. The UK Air Safety Group, through one of its members,
agreed with ATA and suggested the use of higher flash point fuels (such
as JP-5) should be investigated as a possible solution.
    While we welcome the potential for using various forms of FRM, we
do not believe delaying implementation of the rule is in the public's
interest. The FAA and industry participated in ARAC activities that
provided economic analysis of existing technologies, including inerting
and mandatory use of higher flash point fuels. At that time, inerting
was found to be a more cost-effective means of showing compliance with
the performance-based FRM rule. In contrast, as shown in the ARAC
report,\25\ using higher flash point fuels was not the most practical
means of achieving the desired safety level because of the higher cost
of these fuels.
---------------------------------------------------------------------------

    \25\ Document Number FAA-22997-7 in the docket for this
rulemaking.
---------------------------------------------------------------------------

    If technology and refining capabilities have advanced to the point
where higher flash point fuels are available in quantity at a
competitive cost, the industry may use that means to show compliance,
and this means is discussed in the proposed AC 25.981-2. Flammability
assessments with a specified minimum fuel flash point, in conjunction
with airplane flight manual limitations requiring use of such fuel,
could be used as a means of compliance with this rule. Since the rule
is performance-based and does not mandate any particular solution,
industry may find innovative ways to show compliance to standards.
2. Inerting Systems Could Create Ignition Sources
    Transport Canada expressed concern that adding inerting systems to
fuel tanks may create ignition sources and result in additional heating
of in-fuselage tanks. It argued the solution may inadvertently increase
flammability exposure. Transport Canada recommended the FRM be designed
to ensure its reliable operation and minimal maintenance. The UK Air
Safety Group, through one of its members, also expressed this concern.
The commenter suggested that inerting systems could actually compromise
the fuel tank system, that insulation could impede inspections of
equipment and structure, and that ventilation could cause performance
penalties.
    We acknowledge the commenters' concerns that installing FRM could
introduce negative safety consequences. However, these potential
consequences do not outweigh the safety benefits of flammability
reduction. As with all safety equipment, the FRM must comply with the
existing applicable airworthiness standards that are intended to
prevent system failures from having a negative safety impact. In
addition, we have introduced new requirements in this rule to address
the possible negative safety impact of using an onboard nitrogen
inerting system. Compliance with these combined requirements should
produce systems that are reliable, maintainable, and meet the
flammability requirements of this rule.
3. Instruments to Monitor Inerting Systems
    ATEXA recommended that when a nitrogen dilution system is used, the
airplane should be equipped with instruments to verify that the system
is functioning as expected. These instruments should record data
continuously so the pilot can control the oxygen concentration in the
tanks within prescribed limits on the ground, before take-off, and at
landing. This data should also be recorded in the flight data recorder
so that, should another accident happen, the cause/origin could be
identified.
    As we stated before, this rule is performance based and allows
designers the ability to be innovative. The need for indications and
controls is design dependent, and the blanket requirement recommended
by ATEXA could be overly stringent. DAHs may choose to provide flight
crew indications of FRM status, or they may propose an automated FRM
with built-in test to verify proper operation. It would be
inappropriate for the rule to mandate specific design features.
    As for the suggestion to record data, adding additional parameters
to the FDR would be cost-prohibitive. Furthermore, we do not consider
this necessary because the functioning of any FRM or IMM would likely
not have any direct bearing on determining the cause of an accident.
The flammability exposure of the fuel tank is not actually an indicator
that a tank has exploded and the determination that a fuel tank
explosion caused an accident could be made using physical evidence.
    In a related comment, the Shaw Aerospace team (Shaw) commented that
failure monitoring of system operation is inadequate. As proposed, the
system relies totally on the built-in test to detect when the tanks are
not inert due to a failure rather than direct measurement of the fuel
tank oxygen concentration to determine if the tank is flammable. Shaw
cited factors such as oxygen evolution from the fuel as the airplane
climbs and local areas of high oxygen in the tanks because of lack of
adequate nitrogen distribution as sources of flammability that will not
be detected by monitoring the performance of the FRM, rather than
measuring the oxygen concentration in the tank. Shaw stated that if the
oxygen concentration in the fuel tank ullage is not monitored and
periodically sampled, it would be difficult to prove the effectiveness
of the system.
    From the Shaw team's comments, we infer that Shaw believes the
monitoring requirements should be modified to require ullage sampling
to ensure that the tank remains non-flammable. We do not agree that a
change to the proposed regulation is needed. Compliance methods are
discussed in AC 25.981-2. Applicants may choose to measure fuel tank
oxygen concentration directly or infer the concentration through system
performance capability and monitoring. Appendix M25.2 requires that
localized higher concentrations of oxygen that

[[Page 42473]]

might result from inadequate distribution of nitrogen, as well as the
possible effects of oxygen evolution from the fuel, be addressed in the
compliance demonstration.
4. Risk of Nitrogen Asphyxiation
    If fuel tank inerting is used to reduce the flammability exposure
of a fuel tank, several commenters noted that the introduction of
nitrogen enriched air within the fuel tank, and possibly in
compartments adjacent to the tank, could create additional risk because
of the lack of oxygen in these areas. They believe the risk to
maintenance personnel from nitrogen asphyxiation may exceed any safety
benefit that fuel tank inerting may provide. To support their position,
these commenters cited the Fuel Tank Inerting Harmonization Working
Group's (FTIHWG) 2002 Final Report (24-81 lives could be lost between
2005-2020 due to asphyxiation while servicing transport airplanes) and
other industrial accident data showing that oxygen depleted atmospheres
account for significant loss of life. The commenters are concerned that
we have failed to consider this potential loss of life that will result
from this rule.
    We acknowledge that special precautions are needed for worker entry
into confined spaces where fuel vapors or nitrogen enriched air may be
present. The standard practice of U.S. industry today is to comply with
existing Occupational Safety and Health Administration (OSHA)
requirements. These requirements have resulted in ventilating fuel
tanks with air and measuring the oxygen concentration before entry into
a fuel tank. In addition, persons entering a fuel tank must wear
respirators as well as oxygen monitors to alert them should the oxygen
concentration be insufficient.
    The introduction of nitrogen into a fuel tank does not change the
existing requirements for personnel to enter a fuel tank. No new
training or changes to fuel tank entry procedures should be needed as a
result of this rule. Since there are already specific OSHA requirements
for fuel tanks that would prevent any fatalities, any loss of life
would be due to non-compliance with OSHA regulations, not this
rulemaking. Despite these existing OSHA requirements and the
protections they afford, we have added new requirements for markings to
notify workers at all access points and areas of the airplane where
lack of oxygen could be a hazard. For these reasons, we have not
included costs for loss of life due to asphyxiation in the final
regulatory evaluation for this rulemaking.
    We are also not persuaded by the commenters' reference to the
FTIHWG 2002 Final Report. The predicted number of fatalities in that
report is based upon application of data from every possible cause of
nitrogen asphyxiation that is included in data collected between 1980
and 1989 by the U.S. National Institute of Occupational Safety and
Health. The data quotes a total number of fatalities for all causes,
including cases such as bottled nitrogen being hooked up to oxygen
systems at a nursing home. This bulletin is not based upon data that
can easily be applied to the aviation industry and does not provide any
data that could be used to predict a rate of fatalities for the
specific circumstances relating to airplane fuel tank safety. In
addition, we do not think it is appropriate to extrapolate the data
from the bulletin without taking into account existing OSHA
requirements used in the aviation industry or that the placards
required by this rule will heighten awareness to the risks associated
with entering fuel tanks.
5. Warning Placards
    This rule attempts to reduce the risk of nitrogen asphyxiation by
requiring markings on the access doors and panels to the fuel tanks
with FRMs, and to any other enclosed areas that could contain hazardous
atmosphere. These markings will warn maintenance personnel of the
possible presence of a potentially hazardous atmosphere. Bombardier
commented that the use of placards and the exact wording proposed is
too prescriptive. Bombardier recommended the rule require a general
warning, with guidance defining methods of compliance placed in the
corresponding AC 25.981-2.
    The requirement for placards is based upon methods used throughout
aviation and other industries where safety warnings are needed to
protect workers from possible harm. Locating the requirements in the
regulation rather than in advisory material provides appropriate level
of regulatory review of this safety critical information and will
result in standardizing the means of warning maintenance personnel.
Applicants may apply for a finding of equivalent safety should they
wish to propose an alternative means of achieving the level of safety
provided by the placard requirement in the rule.
6. Definition of ``Inert''
    A fuel tank is considered inert when the bulk average oxygen
concentration within each compartment of the tank is 12 percent or less
from sea level up to 10,000 feet altitude, then linearly increasing
from 12 percent at 10,000 feet to 14.5 percent at 40,000 feet altitude,
and extrapolated linearly above that altitude.
    Several commenters, including Airbus, AAPA, AEA and Blaze Tech,
questioned whether an allowable oxygen concentration of 12 percent
would inert a fuel tank. They pointed to comments in an FAA research
document stating that ``(f)urther experiments to examine the trend of
peak pressure rise as a function of both altitude and oxygen
concentration are needed.'' The commenters stated that this is an
indication that the 12 percent oxygen concentration limit would not
prevent the ignition of fuel vapors from rupturing an airplane fuel
tank and that further work is necessary before accepting the 12 percent
value. American Trans Air and ATEXA noted that the chemical process
industry, as quoted by the French National Institute for Research and
Security (INRS, 2004), uses a safety factor of 0.5 for industrial
volumes on non-homogenous fuels, and operators must strive to maintain
a maximum oxygen content of 5 percent for inerting purposes. Based on
this, American Trans Air and ATEXA stated that the 12 percent limit
would not be safe.
    In 1997, we initiated research activity to determine a maximum
oxygen concentration level at which civilian transport category
airplane fuel tanks would be inert from ignition sources resulting from
airplane system failures and malfunctions. Our testing determined that
a maximum value of 12 percent was adequate at sea level. The 12 percent
value was initially based on the limited energy sources associated with
an electrical arc or thermal sparks that could be generated by airplane
system failures and lightning on typical transport airplanes and was
not intended to include events such as explosives or hostile fire.\26\
As a result of this research, we learned that the quantity of nitrogen
needed to inert commercial airplane fuel tanks was less than previously
believed. An effective FRM can now be smaller and less complex than
earlier systems that were designed to meet the more stringent military
standards intended to prevent ignition from high energy battle damage.
---------------------------------------------------------------------------

    \26\ These test results are available on our Web site: http://
www.fire.tc.faa.gov/pdf/tn02-79.pdf as FAA Technical Note ``Limiting
Oxygen Concentrations Required to Inert Jet Fuel Vapors Existing at
Reduced Fuel Tank Pressures,'' report number DOT/FAA/AR-TN02/79.
---------------------------------------------------------------------------

    The 12 percent value is further substantiated by the results of
live fire testing conducted by China Lake Naval Weapons Center that
showed a 12 percent oxygen concentration prevents

[[Page 42474]]

ignition, even when high energy incendiary rounds were used that had
ignition energies well in excess of any source anticipated to occur on
a commercial airplane. These data show that 12 percent oxygen
concentration for commercial airplanes achieves a comparable level of
protection against catastrophic fuel tank explosions as the traditional
9 percent value used by the military for combat airplanes. The
suggestion that the oxygen concentration should be limited to 5 percent
is impractical for commercial airplanes since a significantly larger
flammability reduction system would be needed and, based upon these
test results, there would be no appreciable improvement in airplane
safety.
    Finally, the quoted FAA comment that additional testing is needed
was taken out of context. The recommendation for additional testing
referred to conditions when the oxygen concentration was between 1 to
1.5 percent greater than the limit of 12 percent. Testing at these
higher oxygen concentration values was not extensive since the focus of
the testing was to establish the limiting oxygen concentration where
ignition was not possible. Our report's suggestion that additional
experiments are needed was not an indication that the 12 percent limit
was inadequate--quite the opposite. In fact, the next sentence of the
report confirms the importance of the study's validation of the 12
percent limit: ``The results contained in this report should be useful
in the design, sizing, and optimization of future airplanes inerting
systems and add to the overall knowledge base of jet fuel flammability
characteristics.'' \27\
---------------------------------------------------------------------------

    \27\ Document FAA-22997-14, Executive Summary.
---------------------------------------------------------------------------

7. Use of Carbon Dioxide
    An individual commenter stated that inerting a fuel tank with
carbon dioxide may introduce new concerns because of the solubility of
this gas in fuel and the possible effects on fuel system operation.
This commenter also wanted to know what the acceptable level of oxygen
would be to consider the fuel tank ullage inert when this gas was used.
    We acknowledge the use of carbon dioxide for inerting may require
special considerations for fuel feed system performance. The subject of
inerting with carbon dioxide is addressed in AC 25.981-2 and we have
revised it to highlight these concerns. As for the commenter's specific
question about oxygen concentration in the fuel tank, the acceptable
level of oxygen is the same as if nitrogen is used.
8. Environmental Impact of FRM
    The UK Air Safety Group, Phyre Tech and one individual questioned
the environmental impact of using FRM to displace air and fuel vapor
from the fuel tanks into the surrounding environment. These commenters
expressed concern about increased hydrocarbon emissions into the
atmosphere.
    The IRE did not include an environmental assessment or analysis
because we determined the environmental impact of a FRM or IMM to be
negligible. Their installation will not affect the amount of fuel
vapors and hydrocarbon emissions that are discharged from fuel tanks
during refueling. Currently, fuel tank designs vent fuel vapors and
hydrocarbon emissions into the atmosphere when air is exhausted from
the fuel tanks during refueling and flight. Data from recent flight
tests of a Boeing 737 equipped with a nitrogen-based FRM showed that
installation of FRM and related design changes actually reduce the
amount of hydrocarbons vented from the tanks during flight.\28\ In
those test flights, the data indicated that pressure differences from
one wing tip to the other wing tip, where the two airplane fuel tank
vent outlets are located, resulted in cross flow of air through the
fuel tanks including the center wing tank for the original vent
configuration. This occurred often in flight and periodically on the
ground when any crosswinds were present. As a result, fuel vapors were
exhausted from the fuel tanks into the atmosphere. Any air that entered
the fuel tank diluted the nitrogen concentration in the tank such that
the fuel tank vent outlets needed to be modified to prevent cross flow
of air through the vent system. Modification of the vent system
resulted in reduced hydrocarbon discharge to the atmosphere.
---------------------------------------------------------------------------

    \28\ Data from flight testing on the Boeing 737 (DOT/FAA/AR-01/
63, ``Ground and Flight Testing of a Boeing 737 Center Wing Fuel
Tank Inerted With Nitrogen-Enriched Air,'' dated August 2001).
---------------------------------------------------------------------------

9. Current FRMs Fail To Meet Requirements
    Transport Canada noted that an FRM must meet not only the
requirements in this rule, but also the relevant other sections within
part 25, in particular Sec.  25.1309. Transport Canada stated that
current FRM designs would not meet Sec.  25.1309 because of a lack of
system redundancy, a lack of appropriate system performance monitoring
and indication, and the allowance of MMEL relief.
    We do not agree that existing FRM systems do not meet all the
relevant sections of part 25, including Sec.  25.1309. We approved the
FRM systems for the Boeing 747-400 and 737NG series airplanes in August
2005, and December 2006, respectively, as showing compliance with all
the applicable part 25 regulations. This approval was validated by EASA
shortly thereafter. While the commenter is correct that these systems
lack redundancy, and limited dispatch with the systems inoperative is
allowed under the MMEL, these systems are supplementary safety systems
that are intended to work in combination with the ignition prevention
features required by Sec.  25.981 to prevent future fuel tank
explosions.
10. FRM Based on Immature Technology
    Airbus had numerous objections regarding our description of the
prototype hybrid onboard inert gas generation system (OBIGGS) that was
tested on an Airbus A320 in 2003. Airbus objected to the OBIGGS being
called a ``prototype.'' Instead, Airbus would characterize the OBIGGS
as ``laboratory demonstration equipment.'' Airbus (and AEA) commented
that the OBIGGS was not in an advanced state of development and would
require extensive development before it reached a level of maturity
suitable for certification and operation. Airbus also stated that we
have not identified to Airbus an existing regulation that would require
Airbus to develop an FRM, and Airbus is not committed to any such
development program. British Airways also expressed concerns that the
proposed systems have not been fully tested or developed and operators
may find themselves required to install a system that is not yet fully
certified.
    We acknowledge that the development and certification of a
production and retrofit FRM would require significant engineering and
development. While the FRM equipment (i.e., FAA-developed prototype
OBIGGS) installed and flown on an Airbus airplane had not been
certified, an FRM system similar in concept was designed, tested, and
certified on Boeing 737 and 747 series airplanes within two years of
the Airbus demonstration flights. This certification demonstrates that
the technology is mature, and that our proposed two-year compliance is
reasonable and achievable. The harmonized certification requirements
for the Boeing 737 and 747 FRM, which were nearly identical to those
proposed in the NPRM, were published as Special Conditions in 2005 for
public comment.

[[Page 42475]]

This provided the public, including Airbus, with detailed information
needed to develop an FRM. In addition, much of the hardware and
components needed for an FRM have been developed by aerospace
manufacturers and this developmental work should reduce the time needed
for Airbus to develop a system.
    During development of the NPRM, Airbus provided us with a cost
analysis for an FRM that included the cost of engineering, components
and operation of the system. We trust that the cost information was
based upon initial engineering assessments of FRM and contact with
component vendors. We concur with Airbus that, prior to this final
rule, there was no regulation that would require a flammability
reduction means to be developed and installed. However, since the NPRM
was published, two Boeing 737 and two Boeing 747 airplanes have been
delivered with operational FRM based upon nitrogen inerting technology.
These systems have performed very well and provide an indication that
the technology is mature for application to commercial aviation. In
addition, in its March 5, 2007, letter, Airbus confirmed information it
shared with FAA in November 2006, that Airbus is proceeding with the
development of an FRM (Docket No. 22997-149).

J. Compliance Dates

    The Families of TWA Flight 800 Association, Inc., as well as
several members of the public, commented that the compliance times are
too long and should be shortened. While we understand the commenters'
frustration with the proposed compliance times, the schedules chosen
are based on the industry's ability to respond to this rule. Each DAH,
operator, and after-market modifier will have to follow a series of
steps to make appropriate assessments and develop designs and
installation plans. Designing FRM for each affected airplane model will
require engineering resources; allowing less than 24 months for
developing the design changes is not practical and could result in
unintended reduction in airplane safety because of increased likelihood
of design errors. Accelerating the retrofit schedule could
significantly increase the cost of the program due to the need to
introduce FRM into operators' fleets during lengthy out-of-sequence
maintenance visits. We believe that the schedules chosen correctly
balance the risk of a fuel tank explosion during the compliance period
with the industry implementation capability.
1. Part 26 Design Approval Holder Compliance Dates
a. Submitting the Flammability Exposure Analysis
    Boeing requested that proposed Sec.  25.1815(b)(1) (now Sec.
26.33(b)(1)) be revised to remove the compliance time (i.e., 150 days
after the effective date of the rule) for TC holders to submit the
flammability exposure analysis for affected airplane fuel tanks. Boeing
stated that a large amount of test data is required to develop the
analysis and, as such, a compliance time of 150 days would be
inadequate. They believe this requirement is primarily for program
planning purposes and that the compliance time in Table 1 of proposed
Sec.  25.1815(d) is appropriate for that purpose.
    Embraer and Bombardier similarly commented that the 150-day
compliance time for submitting the flammability analysis is inadequate.
The basis for their comment was that validation of fuel tank thermal
models will require developing new flammability tools and flight
testing, which will require additional time. Embraer proposed a 24-
month compliance time, and Bombardier proposed a 12-month compliance
time.
    We believe the proposed compliance time is adequate. It will ensure
that the flammability exposure analyses are completed for every
affected fuel tank in a timeframe we consider acceptable because of the
reduced amount of work required for conventional unheated aluminum wing
tanks. These analyses will determine if FRM is required for a given
fuel tank, and the timeliness of completing the analysis is needed to
meet the design and implementation schedule. As discussed earlier, we
have revised proposed Sec.  25.1815(b)(2) (now Sec.  26.33(b)(2)(i)) of
the final rule to allow TC holders to avoid performing the flammability
analysis for particular tanks by stating in their compliance plans that
they will treat the tank as high flammability and develop FRM or IMM,
as required. In addition, no flammability analysis will likely be
required to determine the flammability of the center wing tanks of
Boeing and Airbus models, since we have determined from their comments
that these models exceed the 7 percent limit. We have also
significantly reduced the complexity of fuel tank thermal analyses that
will be required by the industry because we modified the analysis
requirements to allow a qualitative flammability assessment for
conventional unheated aluminum wing tanks. No flight testing would be
needed to gather data for conventional unheated aluminum wing tanks.
    For the remaining tanks for which a flammability assessment is
needed, the DAHs have been aware of the need to address fuel tank
flammability and have conducted testing of airplanes to develop fuel
tank thermal models. Therefore, additional time should not be needed to
develop fuel tank thermal modeling for the majority of fuel tanks in
the fleet. We believe 150 days is sufficient to complete the required
analyses, and have made no change to the compliance time in the final
rule.
b. Submitting a Compliance Plan for Developing Design Changes and
Service Instructions
    Under proposed Sec.  25.1815(h), each holder of an existing TC
would need to submit to the FAA Oversight Office a compliance plan for
developing design changes and service instructions within 210 days of
the effective date of the rule, which equals 60 days after the
compliance date for submitting the flammability analysis. Embraer and
Bombardier claimed developing a compliance plan within 60 days of
submitting the flammability analysis was impractical. They based their
objections on the fact that Boeing and Airbus, who are specifically
cited in the NPRM, were already preparing for compliance prior to
publication of the NPRM. They claimed that those DAHs not cited in the
NPRM are not doing advanced preparation and will need extra time.
    While Airbus acknowledged that 210 days is a reasonable timeframe,
Airbus was concerned about how this timeframe would accommodate delays
caused by our review. For example, if the TC holder delivers a
flammability analysis which indicates a value under 7 percent, and,
after review, the FAA identifies failings resulting in a value above 7
percent, the TC holder would then have significantly less time to draw
up any potential compliance plan. Airbus stated that, in such cases, it
could be unreasonable for us to require the TC holder to comply within
210 days. Therefore, Airbus suggested that we consider removing the
fixed time period of 210 days and allow 60 days after the FAA and TC
holder have agreed that the correct result is greater than 7 percent.
It noted the requirements on operators of such airplanes should also be
adjusted by a similar time.
    We do not agree with this suggestion. Airbus provided comments to
the NPRM that its airplane models have HCWT with flammability that
ranges between 9 and 16 percent. Boeing has

[[Page 42476]]

previously provided a statement to the FAA in response to SFAR 88
evaluations that all of its airplane models with HCWT are above the 7
percent value that determines when an FRM or IMM is needed. Based upon
this information we have determined that all Boeing and Airbus models
specifically listed in proposed Sec.  25.1815 (now Sec.  26.33) have
center wing fuel tanks that will require an FRM or IMM. Since the
analysis needed to determine whether the affected tanks would require
an FRM or IMM is already completed, Airbus and Boeing can begin
developing compliance plans for design changes immediately after
publication of this final rule. Similarly, if Embraer and Bombardier
believe their tanks may be high flammability, they should also begin
developing compliance plans for design changes immediately after
publication of this final rule.
c. Service Instruction Submittal Dates
    Airbus and Boeing recommended that the compliance dates for each
airplane model shown in Sec.  25.1815(d), Table 1, be replaced by a
specific time period for all airplanes in the table. Boeing suggested
the same two-year compliance period be applied to all affected models
to allow adequate time to complete design development, validation and
certification of flammability reduction systems, and development and
validation of service bulletins. Boeing stated that this two-year
period would provide the required timing for airline coordination and
parts procurement flow time needed to support the beginning of the
retrofit period. Airbus suggested 36 months is required to develop the
system design and that an additional 6 months should be provided to
allow for an in-service evaluation of the FRM so that any problems with
the design could be identified and corrected before implementation into
the fleet by the operating rules. Embraer requested a compliance time
of 48 months to develop the design change. Cathay similarly commented
that, while Boeing is making advanced preparations, Airbus is not.
Cathay also requested that the compliance time be extended to support a
more ``realistic'' FRM development schedule. Cathay also commented that
the FAA states ``the proposed compliance date is based on the premise
that the NPRM was to be issued in 2005.'' The new compliance dates need
to be revised to reflect delays in issuing the final rule. Bombardier
felt that 24 months for the design changes should only commence once
the authorities have accepted the design change plan.
    We agree with the commenters that a fixed time for all airplane
models should be established. We have determined that a 24-month
compliance time for DAH development of the IMM or FRM is adequate for
each of the DAHs to complete the task. Since we have determined from
the comments that the Airbus and Boeing models listed in Table 1 in the
NPRM require FRM or IMM, no flammability analysis is needed before
design development begins. The full 24-month time can, therefore, be
used by Airbus and Boeing to develop the design and service
instructions for our approval.
    In addition, Airbus and Boeing have had significant notification of
this rulemaking. In February 17, 2004, we made a public announcement of
our plans to develop and publish a proposal to require both retrofit
and production incorporation of FRM or IMM. The NPRM was issued in
November, 2005, and the rulemaking processing time has provided
extensive time to develop designs as well as work with suppliers to
discuss cost and schedule issues. Special conditions for the Boeing 737
and 747 were published by the FAA and EASA that provided performance
standards for FRM in 2005. Many of the components in nitrogen based FRM
systems are similar or identical to components used in military
applications or pneumatic systems on commercial airplanes. The air
separation modules used in these systems are based on technology
currently used extensively in other industries. Therefore, we believe
Airbus's request to increase the development and certification time
from 24 months to 42 months, and Embraer's request for 48 months, are
excessive, and we are confident that 24 months provides adequate time
for design and service instruction development. Extending this
compliance time would delay the operators' installation of these
important safety improvements. Therefore, we have not revised the final
rule as requested.
2. Operator Fleet Retrofit Compliance Dates
    In proposed Sec. Sec.  91.1509, 121.1117, 125.509 and 129.117, we
included a Table 1 that contained the interim and final compliance
dates for operators to complete the installations of IMM, FRM or FIMM
required by those sections. Table 1 proposed unique compliance dates
for those affected Boeing and Airbus models with high flammability fuel
tanks. These dates were selected based upon the availability of service
instructions and the risk associated with each airplane model.
a. Removal of Unique Compliance Dates for Affected Airplane Models
    Boeing stated that, assuming the FAA concludes that retrofit is
justified, the compliance time should be 7 years from the date that
service instructions are available for all airplane models. Boeing
maintained there is no justification for requiring unique compliance
times tied to airplane models and recommended deleting Table 1.
    We agree and have removed Table 1 from the final rule. This table
has been replaced with a standardized compliance date for all affected
airplanes. As explained below, the new compliance time for all models
is 9 years from the effective date of this rule. We did not link the
operators' compliance time to our approval of the service instructions
because the length of time it will take us to approve the submission
will depend upon the quality of the submission. While the compliance
planning provisions are intended to ensure that the submissions are
approvable, whether they have that effect is within the control of the
DAHs.
b. Increase Compliance Times From 7 to 10 Years
    The ATA asked that the compliance times be increased from 7 to 10
years after manufacturers develop the necessary design changes. ATA
argued that the accident rate is such that there is little risk of
catastrophic in-flight fuel tank explosion during that period. A 10-
year compliance time would allow all operators to incorporate the FRM
in heavy maintenance visits instead of only 85 percent of them.
    We partially agree with ATA. As discussed previously, we are
providing a compliance time of 24 months for all affected manufacturers
to develop necessary design changes. We have adjusted the compliance
times in the operational rules to allow 6 years after the effective
date for compliance by 50 percent of an operator's fleet, and 9 years
for full implementation, i.e., we are retaining the compliance time of
7 years after the design changes are developed. The compliance period
of 7 years for operators to incorporate the design modifications into
each fleet was selected to allow the vast majority of the FRM or IMM to
be incorporated during airplane heavy checks and to achieve the safety
level expected by the public.
    Nevertheless, as ATA noted, 15 percent of the airplanes may need to
incorporate FRM at a time other than during a heavy check. To address
this concern and reduce the costs of this rule, we have revised the
operational requirements of parts 121 and 129 to

[[Page 42477]]

allow a one-year extension for retrofit if the operator elects to use
ground conditioned air for all airplanes with high flammability tanks
(i.e., Boeing and Airbus models) for ``actual gate times'' exceeding 30
minutes when ground air is available at the gate and operational and
the ambient temperature exceeds 60 degrees F. This approach responds to
requests for more time to retrofit while providing compensating risk
reduction by use of ground conditioned air, which reduces flammability
for airplanes on the ground. We are not including this extension
provision in part 125, because these airplanes are typically not parked
at gates where ground conditioned air is available. Also, these
operators typically only operate one or very few airplanes subject to
this rule, so they will not encounter the difficulties that ATA
identified in scheduling large fleets of airplanes for modifications.
    For purposes of this provision, ``actual gate time'' is time when
the airplane is parked at a gate for servicing and passenger egress and
ingress. If scheduled gate time is 30 minutes or less, but departure is
delayed so that airplane is parked for more than 30 minutes, use of
ground air is required for any period longer than 30 minutes. This
ensures that heating of tanks (and resulting increased flammability) is
limited. ``Available'' means installed at the gate. ``Operational''
means working, so that an operator is not in violation simply because
ground conditioned air is out of service for maintenance. Ambient
temperature is the official temperature at the airport as provided by
the U.S. National Weather Service or worldwide METAR \29\ weather
report system. This provision requires revision of operator's
operations specifications and relevant manuals to ensure that the
commitment to use of ground air is fully implemented and enforceable.
In the near future we will be issuing guidance on compliance with the
conditions for this extension.
---------------------------------------------------------------------------

    \29\ METAR (from the French, ``message d'observation
m[eacute]t[eacute]orologique r[eacute]guli[egrave]re pour
l'aviation,'') is a format for reporting weather information. METAR
means ``aviation routine weather report'' and is predominantly used
by pilots in fulfillment of a part of a pre-flight weather briefing,
and by meteorologists, who use aggregated METAR information to
assist in weather forecasting.
    METAR reports usually come from airports. Typically, reports are
generated once an hour; however, if conditions change significantly,
they may be updated in special reports called SPECI's. Some reports
are encoded by an Automated Surface Observing System located at
airports, military bases and other sites. Some locations still use
augmented observations, which are recorded by digital sensors and
encoded via software, but are reviewed by certified weather
observers or forecasters prior to being transmitted. Observations
may also be taken by trained observers or forecasters who manually
observe and encode their observations prior to their being
transmitted. Source: Wikipedia, August 2007.
---------------------------------------------------------------------------

c. Interim Compliance Dates
    We proposed interim compliance dates for operators to incorporate
any FRM or IMM into 50 percent of their affected high flammability
airplanes within their fleet. Boeing requested we revise Sec. Sec.
91.1509(d)(1), 121.1117(d)(1), 125.509(d)(1), and 129.117(d)(1) to
state:
    ``IMM, FRM or FIMM, if required by Sec. Sec.  25.1815, 25.1817, or
25.1819 of this chapter, that are approved by the FAA Oversight Office,
are installed in at least 50 percent of the operator's fleet within 4
years from the date service instructions are available. This does not
apply for certificate holders with only one airplane in the fleet.''
    Boeing stated that newly delivered airplanes should be included in
the operator's ``fleet'' for purposes of Table 1. Boeing also commented
that Table 1 should not be split by individual airplane model, but
should include all airplanes in a given operator's current fleet. The
recommended revision to 50 percent of the operator's fleet should also
specify if this is 50 percent of their fleet operating on the
compliance date, 50 percent of their fleet that is operating at the
beginning of the compliance period, or 50 percent of their fleet that
will be operating at the end of the compliance period.
    We agree that additional clarification is needed on the definition
of ``50 percent of fleet.'' We intended that the 50 percent figure be
based on all airplanes that are required to be modified under this rule
and that are being operated by an operator 6 years after the effective
date of this rule. Any airplanes transferred or purchased with high
flammability fuel tanks, would be included in the operator's ``fleet.''
Since newly delivered airplanes are not required to be modified, they
are not included as part of the 50 percent of the fleet to meet this
requirement.

K. Cost/Benefit Analysis

    As noted in the Regulatory Evaluation Summary, specific comments on
the quantitative costs and benefits estimates are more completely
discussed in the FRE. In this section, we only address general economic
issues that were addressed by the comments.
1. Security Benefits
    In the NPRM, we noted that the potential benefits from preventing
terrorist-initiated accidents were excluded from consideration in both
the ARAC reports and the IRE. While the proposed FRM requirements were
not primarily intended to address terrorist-initiated explosions, we
invited public comment on possible additional security benefits that
inerting fuel tanks may provide. In response to this request, we
received several comments, including the following:
     The NTSB and several individuals supported including
benefits from prevented consequences of terrorist action in the FRE and
suggested we should complete a cost/benefit analysis of inerting all
fuel tanks to address terrorist threats. The NTSB noted that, although
not intended for missile defense or entirely effective as such,
flammability reduction systems could mitigate the results of shrapnel
entering fuel tanks during a terrorist act. Therefore, the NTSB
recommended that the cost-benefit analysis for the final rule should
include estimates of potential missile attacks on airplanes. In
addition, these commenters also supported including possible benefits
from preventing terrorist actions caused by bombs exploding in the
airplane.
     CAPA stated that the United States is at a heightened risk
of terrorist attacks. CAPA noted the aviation industry affects nearly 9
percent of the U.S. Gross Domestic Product, and suggested that
terrorists will undoubtedly seek ways to attack the aviation
infrastructure. CAPA recommended that we should complete a cost benefit
analysis of inerting all fuel tanks and make recommendations to the
Department of Homeland Security and aviation industry.
     NATCA commented that there would be an adverse effect on
the public's confidence in flying if another fuel tank explosion
occurred.
     Airbus and AEA stated that, in theory, there may be some
benefit to improving security by installing FRM on airplanes. However,
they noted that we have no basis for estimating the amount of that
benefit and they do not believe it to be substantial.
     ATA and FedEx objected to the FAA's including the Avianca
727 accident in its justification of this rule. They stated that this
accident, which resulted from a small bomb placed above the center wing
fuel tank on the previous flight, would not have been prevented by the
requirements of this rule.
    Based upon the comments received and our review of historical
evidence, we have not quantified any potential benefits from an FRM
system preventing a fuel tank explosion caused by a terrorist missile
or an on-board bomb.
    We have also not quantified the potential benefits from a fuel tank
explosion being misinterpreted as a terrorist-caused event because such
an

[[Page 42478]]

outcome is too speculative to include in the main body of the analysis.
However, we have provided a quantified estimate of the possible
benefits from preventing this misinterpretation in Appendix A of the
FRE.
    However, some of the public will cancel or curtail their air travel
after they discover that the in-flight accident was caused by an
airplane electrical or mechanical malfunction. An in-flight explosion
is a catastrophic accident. There is a long history that air travel
declines for two to three months after a major catastrophic accident.
We use a study by Wong and Yen, ``Impact of Flight Accidents on
Passenger Traffic Volume of the Airlines in Taiwan'', in the Journal of
Eastern Asia Society for Transportation Studies, vol. 5, October 2003,
to provide an estimate of the potential demand losses from a fuel tank
explosion.
2. Likelihood of Future Explosions in Flight
    The IRE assumed that all future accidents caused by fuel tank
explosions will occur in flight. This assumption was based upon an
evaluation of the flammability exposure times for various flight phases
that showed the majority of the time fuel tanks are flammable is during
flight. The method used by us in the IRE to estimate the likelihood of
future explosions occurring in flight or on the ground was based upon
an earlier version of the Monte Carlo model, ``Fuel Tank Flammability
Assessment Method User's Manual, DOT/FAA/AR-05/8.'' This earlier model
used ground times of 30, 60 and 90 minutes for short, medium, and long-
range airplanes. Using this model, we determined 90 percent of the
flammability exposure time occurred during flight. We then simplified
the IRE by assuming all future accidents would occur in flight.
    Our review of recent fleet data collected from in-service airplanes
indicates that ground times are longer than used in the earlier version
of the Monte Carlo model. This results in a higher percentage of the
flammability exposure time being when an airplane is on the ground. In
addition, the historical accident rate of one accident out of three
occurring in flight is based upon a limited number of events and is not
a valid sample size for establishing the future accident rate. Since
ignition sources may occur at any time during ground or flight
operations, the ARAC fuel tank study concluded that the likelihood of
future fuel tank explosions correlates to the flammability exposure of
a fuel tank. We agree with this conclusion.
    MyTravel Airlines, AEA, Alaska Airlines, ATA, and Airbus stated
that, the probabilities of an in-flight explosion and an on-the-ground
explosion is the simple extrapolation of the three events; that is,
there is a 33.33 percent probability of an in-flight explosion and a
66.67 percent probability of an on-the-ground explosion. Boeing
commented that its engineering analysis indicated an 80 percent
probability of an in-flight explosion and a 20 percent probability of
an on-the-ground explosion and supported its recommendation with a
recent flammability assessment using a revised Monte Carlo model.
Boeing also recommended that a sensitivity analysis be included in the
regulatory evaluation varying the number of in-flight events by values
of 33 percent or 50 percent. In the GRA, Incorporated appendix to the
ATA comment, they noted that using plausible assumptions in FAA's
model, a better estimate of the percentage of time that a tank is
flammable would be 78 percent in the air.
    We believe that the appropriate method to evaluate the future risk
is through a flammability assessment rather than observations of an
infrequently occurring event. As a result, we agree with the Boeing
analysis and disagree with the ATA and Airbus analyses and revise our
risk analysis so that there is an 80 percent probability that an
explosion will occur in flight and a 20 percent probability that it
will occur on the ground.
    Finally, we do not agree with Boeing's recommendation to include in
the FRE an assessment of the sensitivity of varying the ground versus
flight accidents between 30 and 50 percent. The IRE already included
variations in many factors that affect the predicted cost and benefits
and adding another sensitivity factor would not provide useful data for
determining the need for this rule.
3. Costs to Society of Future Accidents
    Several commenters said the cost of future accidents used in the
IRE did not include all the costs to society. They said the IRE
excluded the costs of investigating the accident, cleanup at the
accident scene, replacement and retraining of flight crew, and any
design change needed to correct failures of parts or systems on the
airplane. They added that an accident would also cause a loss of
confidence in the aviation industry leading to the public reducing
their airline travel. They requested these additional costs be included
in the final rule.
    We agree with some of these comments and, as previously discussed,
we include quantitative estimates of the potential benefits from the
loss of confidence in aviation transport. We disagree that we did not
include accident investigation and clean-up costs because the IRE
contained a specific $8 million cost for the accident investigation.
Although it may occur that design changes will need to be made, these
changes would be done via rulemaking or AD and the costs for those
specific changes would be estimated when proposed.
4. Value of a Prevented Fatality
    AEA and ATA stated that the value of a prevented fatality should be
3 million dollars. AEA stated there is no basis for using a higher
value.
    Different government entities use different estimates of the value
of a prevented fatality. For example, the Environmental Protection
Agency uses a value of $7 million and the Department of Transportation
has historically used a value of $3 million (which we used in the IRE).
There are several different values that have been reported in economic
literature and there is no one value on which there is universal or
near-universal agreement. The Office of Management and Budget allows
agencies to evaluate their cost-benefit analyses using alternative
values for a prevented fatality in order to evaluate how sensitive the
analytic results are to the assumed values. Therefore, we believe that
varying the value to show the range of reasonable effects is
appropriate and we have included values of $3 million, $5.5 million,
and $8 million to provide a better understanding of the sensitivity of
the evaluation to changes in this baseline assumption.
5. Cost Savings if Transient Suppression Units (TSUs) Are Not Required
    The NTSB determined that the probable cause of the TWA Flight 800
explosion was ignition of the flammable fuel/air mixture in the center
wing fuel tank. Although the ignition source could not be determined
with certainty, the NTSB determined that the most likely source was a
short circuit outside of the center wing tank that allowed excessive
voltage to enter the tank through electrical wiring associated with the
fuel quantity indication system (FQIS). We issued ADs mandating
separation of the FQIS wiring that enters the fuel tank from high power
wires and circuits on the classic Boeing 737 and 747 airplanes after
the TWA 800 accident, and this resulted in installation of TSUs as an

[[Page 42479]]

alternative method of compliance with the ADs.
    In the NPRM for this rulemaking, we requested public comment on the
possible cost savings that would occur if airlines were not required to
install transient suppression units (TSUs) on the fuel quantity gauging
systems of the high flammability fuel tanks that would need FRM to
comply with this rule. We received the following responses:
     Several commenters stated that we need to clarify the
requirements for design changes resulting from SFAR 88, since they
believed no additional changes to incorporate TSU would be needed for
their fleet.
     According to ATA, the cost avoidances would be minor,
compared to the impact of the ignition-prevention ADs and pending SFAR
88 maintenance upgrades.
     AEA stated that TSUs will not be removed, so there is no
cost savings. If the TSUs were removed, additional costs would be
incurred for certification, service bulletins, manpower, and hangar
space.
     Airbus and My Travel Airways commented that they
anticipate no significant savings since only a fraction of the fleet is
designed with a need for these devices, and the cost of these devices
is small, compared to the cost of flammability reduction systems.
     Transport Canada commented that ignition prevention should
not be traded off against flammability reduction. Both should be
required.
     Qantas stated that, if these devices could be removed from
its existing fleet, it would realize a significant cost savings in
operations and maintenance. Qantas also said that the cost of these
devices is minimal compared to the installation of an FRM, but if the
FQIS requires replacement of the fuel gauging system to make the
devices effective, it would be similar in cost to an FRM. However,
Qantas noted that an FRM may produce a weight penalty such that a FQIS
replacement would still be preferred.
    Prior to this rule, the findings from the analysis required by SFAR
88 showed that most transport category airplanes with high flammability
fuel tanks needed TSUs to prevent electrical energy from airplane
wiring from entering the fuel tanks in the event of a latent failure in
combination with a single failure. Since this rule requires FRM or IMM
to mitigate an unsafe condition by converting these fuel tanks into low
flammability fuel tanks, TSUs will no longer be needed. Therefore, we
believe it is appropriate to include this as a cost avoidance of this
rule. However, based on the comments that installing these TSUs will
impose a minimal cost, we did not estimate a cost offset for those
airplanes that would have been required to have TSUs installed but are
no longer required to do so under this rule.
6. Corrections About Boeing Statements
    Boeing stated that the IRE has several statements that should be
corrected in the final version. First, Boeing will not provide
engineering analyses via service bulletins or provide initial aid to
large airlines and independent third party repair stations. Boeing
asked that these statements be deleted. Boeing also indicated that it
will follow the regulatory requirements for providing service
information. Finally, Boeing pointed out that the IRE improperly
references STCs where it should be referencing amended TCs.
    We agree with Boeing and have revised these issues in the FRE
accordingly.
7. 757 Size Category
    Boeing noted that the Model 757 was classified as a small airplane
in the IRE and suggested that it be included in the medium category.
Boeing based this on the fact that the Model 757's fuel tank volume and
airplane performance is similar to that of other airplanes categorized
as medium-sized by ARAC.
    We agree and have included the Boeing 757 in the medium category
and have adjusted the weight and cost estimates accordingly.
8. Number of Future Older In-Service Airplanes Overestimated
    Alaska Airlines commented that the IRE overestimated the number of
older in-service airplanes in future years, which artificially
increases the benefits of the FRM retrofit requirements. Alaska
Airlines asserted that industry projects a higher proportion of newer
airplanes versus older airplanes for the projected benefit period.
    The fleet mix in the IRE was based upon our fleet forecast.
Therefore, the number of newer airplanes reflected the official FAA
fleet projections. In the FRE, we have updated the fleet mix data using
the most recent FAA Aerospace Forecasts Fiscal Years 2006-2017. This
forecast projects higher retirement rates than those forecasted in the
FAA Aerospace Forecasts Fiscal Years 2004-2015, which we used in the
IRE.
9. Revisions to the FRM Kit Costs
    ATA, AEA, AAPA, Federal Express, Airbus, and Boeing suggest that we
revise the price of the FRM components because the original ARAC
estimates had not been fully developed and tested and, subsequent to
this additional development, the FRM kit costs are higher.
    Boeing has provided new kit costs for its various models, which are
revised from its previous component costs. We agree with Boeing and use
them in the FRE for production airplanes.
    However, United/Shaw Aero Devices/Air Liquide have recently
developed an FTI system to retrofit in airplanes and they have reported
kit costs. As they have a patent for the system and operational
prototypes, we use the United/Shaw Aero Devices/Air Liquide
retrofitting kit costs in this analysis.
10. Revisions to the Labor Time To Retrofit FRM Components
    Several commenters reported that the labor hours to retrofit an
airplane used in the IRE were too low. In its discussions with the
airlines, Boeing provided an estimated number of labor hours to
retrofit its kits by model. The ATA reviewed these estimated hours and
commented that its expected labor hours were approximated 25 percent to
40 percent higher than the preliminary numbers provided by Boeing.
Qantas reported that the retrofitting labor hours are 50 percent
greater than those in the service bulletins.
    However, the United/Shaw Aero Devices/Air Liquide retrofitting kit
is different from the retrofitting kit on which the ATA based its
reported hours. As a result, just as we use the United/Shaw Aero
Devices/Air Liquide retrofitting kit costs, we also use their labor
hour estimates to install their system.
    However, the labor hours to retrofit these kits will decline over
time due to mechanics becoming more familiar with the installation
procedures. T.P. Wright found that an 80 percent learning efficiency
has been a common occurrence in airplane production. We assume that
this 80 percent learning efficiency also applies to retrofitting
operations.
11. Retrofitting Costs per Airplane
    Cathay Pacific and the AAPA commented that the per airplane
retrofitting costs reported by EASA for an Airbus airplane would be
between $600,000 to about $1 million (converting Euros into Dollars).
Airbus provided similar comments.
    In combining the United/Shaw Aero Devices/Air Liquide kit costs and
their labor hours costs, we calculate that the per airplane
retrofitting costs will initially be $110,000 to $250,000. Over time,
these costs will decline by $10,000 to $17,000 per airplane.

[[Page 42480]]

12. Percentage of Retrofits Completed During a Heavy Check
    Airbus commented that the average time between heavy checks is 10
to 12 years. Thus, 85 percent of the retrofits could not be completed
within the proposed 8 year time-frame.
    We disagree. Our experience has been that the vast majority of
airplanes in commercial passenger service in the United States have
some form of a heavy check no later than every 8 years.
    The AEA commented that 60 percent of the retrofits would be
completed during a heavy check while ATA commented that 85 percent
would be completed during a heavy check. In the IRE, we had used 85
percent.
    We agree with the ATA comment and use the 85 percent value in the
FRE. Operators who choose to take advantage of the extension allowed by
use of ground conditioned air will be able to complete the retrofits of
an even higher percentage of their fleet during heavy checks.
13. Number of Additional Days of Out-of-Service Time To Complete a
Retrofit
    The ATA commented that retrofitting FRM during a heavy check would
add two days of out-of-service time, AEA commented that it would add
two to three days, while Airbus commented that the airlines had told
EASA that it would add one day.
    In the IRE, we had used two days. We agree with ATA and use two
days in the FRE for the out-of-service time if the retrofit is
performed during a heavy check.
    Airbus commented that retrofitting FRM during a medium check would
add 5 days while it would add seven days if completed during a special
maintenance visit. In the IRE, we had used four days out-of-service for
a retrofit performed during a special maintenance visit based on the
ARAC report. Airbus provided no justification for its disagreement with
the ARAC conclusion. As we received no comments other than the Airbus
comment on this topic, we disagree with Airbus and use four days out-
of-service for a special maintenance visit.
14. Economic Losses From an Out-of-Service Day
    Airbus and the ATA commented that the losses to an airline from an
out-of-service day should be based on the airplane on ground economic
loss or the loss in net operating revenue, not a pro-rated monthly
lease rate as used in the IRE.
    We disagree. While it is true that the loss to air carrier A is
greater than the prorated monthly lease rate, most potential air
travelers will use alternative air carrier B if air carrier A takes an
airplane out of service for a short time. Consequently, alternative air
carrier B receives an economic benefit that is not captured by only
focusing on the air carrier airplane that is out of service. The FAA's
responsibility is to cost the potential loss to the aviation system,
not individual air carriers at specific points in time. This is
particularly apparent when alternative air carrier B will need to
remove an airplane from service and air carrier B's air travelers will
use air carrier A that will receive an economic benefit that is not
captured by focusing solely on the loss to air carrier B at that
specific point in time.
    Airbus commented that the FRM cost for its products is
underestimated by a factor of two to three. Based upon review of all
comments, including those based upon a certificated FRM provided by
Boeing, we believe the FAA cost estimates should be revised by a factor
of 1.6 and we have adjusted the regulatory evaluation accordingly. We
applied the revised retrofitted airplane costs for the certificated FRM
systems to all similarly-sized airplane models because we determined
that the fuel tank inerting systems will be similar for both
manufacturers.
15. Updated FRM Weight Data
    Boeing provided updated weight data for the flammability reduction
systems that have been or are being developed for its airplane models.
Boeing stated that the final weights for the Boeing 747-400 and 737-NG
systems are known since the designs have been certified. Boeing
estimated the weight for the Boeing 777 system. As for the Boeing 757
and 767 systems, preliminary designs indicate these systems will be
similar and Boeing estimated the weights based upon comparison to the
other models. Boeing also provided updated estimates for average annual
flight hours for Boeing airplanes.
    We have revised the weight and annual flight hour data in the FRE
for production airplanes based on Boeing's updated information. We also
used this updated data for similarly sized Airbus airplane models.
    United/Shaw Aero Devices/Air Liquide reported that their
retrofitting kits weigh less than the Boeing kits. We used United/Shaw
Aero Devices/Air Liquide kit weights for the retrofitted airplanes.
16. Updated Fuel Consumption Data
    Boeing also provided revised annual fuel consumption due to the FRM
weight and increased bleed flow and ram drag. A GRA, Incorporated
report that surveyed several air carriers provided current air carrier
fuel consumption per pound of additional weight.
    For the annual fuel consumption due to the FRM weight, we have used
the GRA values from the air carriers because we believe the air
carriers will be more accurate in reflecting their actual usage over a
variety of flight mission lengths and conditions than the Boeing
engineers would be. We used the Boeing estimates of the additional fuel
consumption for increased bleed air flow and ram drag in the FRE. We
used these rates for both production and retrofitted airplanes because
United/Shaw Aero Devices/Air Liquide did not provide independent
estimated rates for their kits.
17. Updated Fuel Cost Data
    Several commenters reported that the $1 per gallon aviation fuel
cost used in the IRE no longer reflected the economic reality. For a
cost per gallon, Frontier suggested $2.11, ATA suggested $1.50, Qantas
suggested $2.00, and Airbus suggested $1.50.
    We agree that the per gallon price of aviation fuel has increased.
Based on our FAA Aerospace Forecasts Fiscal Years 2008-2025, we
determined that the average future price per gallon will be $2.01.
Although this fuel price is based on the most recently published FAA
forecast, we recognize that, given the current record high oil prices,
this estimate may underestimate the long term aviation fuel cost.
18. Cost of Inspections
    Air Safety Group, UK commented that the NPRM does not include any
costs associated with the impact of FRM inspections on flight delays
and cancellations. The commenter recommended that the cost/benefit
analysis be revised to take a more realistic account of these
additional operational costs. Boeing's comments included revised
estimates of these costs.
    With respect to flight delays and cancellations due to these
inspections, the DAH requirements allow placing a nonfunctional FRM or
IMM on the MEL provided the overall system performance meets the
minimum criteria. We agree with the revised costs from Boeing on the
costs of delays and cancellations in the FRE and used them for both
production and retrofitted airplanes.

[[Page 42481]]

19. Inspection and Maintenance Labor Hours
    Boeing commented that the annual labor hours for inerting system
inspection and maintenance time should be revised to 6 hours for Boeing
passenger and all-cargo airplanes. Boeing cited design features and
related fault indication systems that will eliminate the need for
scheduled maintenance performance checks on the inerting systems.
Boeing also reported that unscheduled delays will only occur for
failures that require locking the NGS Shutoff Valve closed.
    We agree with Boeing's estimates for both production and
retrofitted airplanes and use them in the FRE.
20. Daily Check
    ATA commented that its estimates for inerting system operational
and maintenance costs are much higher than those used by the FAA. ATA
stated that 15 maintenance minutes per airplane per day will be
required and this was not accounted for by the FAA.
    We infer from ATA's comment that ATA believes that our estimated
maintenance costs should be revised to include a 15 minute daily check
of the FRM. The inerting system certified by the FAA (and validated by
EASA) for the Boeing Model 737NG and 747-400 airplanes did not include
a daily check. Specific features of the design, in conjunction with
indication systems, removed the need for a daily check. We anticipate
that Airbus's design will be similar in that the electronic centralized
airplane monitor will be utilized for FRM status. This would impose no
greater burden on operators than the FRM systems that have been
certified to date. As a result, we have not included costs associated
to a 15 minute daily check of the FRM in the FRE.
21. Spare Parts Costs
    Boeing asked that the inerting system spare parts costs be revised
based on its updated costs from suppliers. Boeing estimated that the
air separator/filter capacity and life is directly related to the
environment in which the airplane is operated. Boeing added that its
filter installation includes monitoring for excessive pressure drop
that is used to determine when the filter needs to be replaced.
Finally, Boeing noted that its expected filter maintenance interval is
greater than one year for average environmental conditions.
    We agree with the cost information provided by Boeing and used the
new cost for the filter element replacement in the FRE. While we
acknowledge the filters will be replaced when the pressure across the
filter is excessive, Boeing did not provide an expected average filter
replacement interval. In general, air separator/filters are expected to
last between 1 and 3 years, depending upon the conditions under which
the airplane is flown. An annual filter element replacement is a worst
case situation. As a result, in the FRE, we use an average filter
element replacement interval of every 2 years.
22. Air Separation Module (ASM) Replacement
    Boeing asked the FAA to revise the cost of ASMs that would need to
be purchased for replacing modules when they reach their design life.
The IRE contained estimates ranging from $5,275 to $28,814. Boeing
stated the revised costs range from $30,520 to $151,000. As United/Shaw
Aero Devices/Air Liquide did not provide an estimate for this cost
component, we applied the Boeing estimate to retrofitted airplanes.
    Boeing also requested that the ASM replacement costs be evaluated
based upon data provided in a table for average annual utilization by
Boeing airplane model. Boeing believed this data is more realistic of
model specific fleet utilization. While the IRE assumed an average
utilization rate of 3,000 flight hours, Boeing's current data for
different models range from 3,000 to 4,250 flight hours for passenger
carrying airplanes and 1,000 to 4,250 for all-cargo airplanes. Finally,
Boeing stated that the design life goal for the ASM remains 27,000
hours. FedEx commented that a manufacturer had told them that the ASMs
will need to be replaced every few years.
    We agree with Boeing that the design goal of an ASM replacement
every 27,000 flight hours will be reached and we use that interval for
the ASM replacement frequencies in this Regulatory Evaluation.

L. Miscellaneous

1. Harmonization
    Several commenters (Boeing, Transport Canada, Alitalia, AAPA,
Virgin, Cathay) expressed the need for harmonization of FAA
requirements with those of other national aviation authorities. These
commenters noted that harmonization with the other major regulatory
agencies would benefit the industry and encourage a broader dialogue.
We agree that harmonization of the fuel tank flammability safety
requirements is usually desirable. Prior to and throughout the
development of this rule, we used several avenues to involve other
foreign regulatory authorities and industry, including:
     Aviation Rulemaking Advisory Committee (ARAC) working
groups comprised of representatives of foreign regulatory authorities
and industry and other interested parties were used to review issues
and provide recommendations for developing and harmonizing this rule.
EASA, Transport Canada and the Brazilian CTA participated in these
working groups, which conducted extensive studies of fuel tank safety.
These studies included a review of the fleet history as well as
evaluating the various options for improving airplane safety through
flammability reduction. One working group was created to review fuel
tank flammability and methods to reduce flammability in the tanks. This
then led to the creation of a second working group that exclusively
reviewed fuel tank inerting. The recommendations from these working
groups became part of the basis for this proposed rule. The
recommendations from the two fuel tank safety ARAC studies guided our
rulemaking proposal and this final rule.
     We also participated in an industry and regulatory
authority group assembled by EASA to review fuel tank flammability
safety and produce an EASA Regulatory Impact Assessment (RIA). This RIA
is available on EASA's Web site at (www.easa.eu.int/doc/Events/
fueltanksafety_24062005/easa_fueltanksafety_24062005_qa_
summary.pdf).
    EASA's RIA recommended production incorporation of FRM on newly
produced airplanes that have high flammability tanks and EASA has
indicated that it plans to propose an amendment to their regulations
applying to new transport airplane designs in CS-25. We anticipate
harmonization of these requirements. However, EASA has not yet
determined that FRM retrofit should be required.\30\ We believe the
fleet operation projections show that the risk of an explosion
occurring on existing airplanes and newly produced airplanes is
similar. This safety issue needs to be addressed, despite the lack of
harmonization, and we have included a FRM retrofit requirement in this
final rule.
---------------------------------------------------------------------------

    \30\ EASA has commissioned a study to reconsider the
desirability of a retrofit requirement.
---------------------------------------------------------------------------

    While we remain committed to the goal of harmonization, our primary
objective in this rulemaking is to improve aviation safety. When we
determine that the need exists for a certain regulation, and the other
regulatory agencies find that a more stringent or lenient requirement
is appropriate, we review their findings

[[Page 42482]]

and will revise our regulation if our regulatory goals are met, an
equivalent level of safety is achieved, and any additional burden
imposed on the industry is justified. This is the approach we have
taken in drafting this rule.
2. Part 25 Safety Targets
    AEA commented that part 25 is missing safety targets and
recommended the final rule include a specific target for both ignition
and flammability reduction. This target could be achieved by ignition
source prevention in combination with flammability reduction. AEA
proposed the target be the same as for any other catastrophic event in
transport category airplanes: 10-9 per flight hour.
    We do not agree with AEA's proposal to include a safety target in
part 25. As discussed previously, because ignition sources are caused
by human error and other unpredictable factors, it is impossible to
assign an accurate probability value to them. Therefore, Sec.  25.981
is based on a balanced approach for preventing fuel tank explosions.
This section provides both ignition prevention plus an additional
safety improvement by controlling fuel tank flammability exposure to an
acceptable level. Today's rule adds requirements for fuel tanks located
in the fuselage contour and extend the mitigation into the fleet of
existing airplanes.

IV. Rulemaking Analyses and Notices

Paperwork Reduction Act

    As required by the Paperwork Reduction Act of 1995 (44 U.S.C.
3507(d)), the FAA submitted a copy of the new (or amended) information
collection requirement(s) in this final rule to the Office of
Management and Budget for its review. OMB approved the collection of
this information and assigned OMB Control Number 2120-0710.
    This rule supports the information needs of the FAA in approving
design approval holder and operator compliance with the rule. The
likely respondents to this proposed information requirement are the
design approval holders such as Boeing, Airbus and several auxiliary
fuel tank manufacturers as well as operators. The rule requires the
certificate holders to submit a report to the FAA twice each year for a
period up to 5 years. Operators who choose to use ground air
conditioning would be required to provide a one time statement of their
intent to use this option. The burden would consist of the work
necessary for:
     DAH to develop flammability analysis reports and the
service instructions for installation of IMM or FRM.
     DAH to develop changes and incorporate a maintenance plan
into the existing maintenance programs.
     DAH to provide bi-annual reliability reports for FRM for
the first 5 years of operation.
     Operators to provide notification to the FAA of their
intent to use ground air conditioning.
     Operators to record the results of the installation and
maintenance activities.
    The largest paperwork burden will be a one-time effort (spread over
3 years) associated with the Design approval holders (TC and STC
holders) to develop design changes. Operators will also need to update
their maintenance programs, including maintenance manuals, to include
the design changes. The basis for these estimates is the industry
Aviation Rulemaking Advisory Committee report, which provided hours for
each of the 3 major areas of paperwork. Based on an aerospace engineer
total compensation rate of $110 an hour, the total burden will be as
follows:

------------------------------------------------------------------------
                                                            Total cost
  Documents required to show compliance        Hours       (in millions
           with the final rule                               of $2007)
------------------------------------------------------------------------
Application to FAA for Amended TC or STC         405,000          44.550
Documents (Specifications, ICDs, etc.)..          30,900           3.399
Revisions to Manuals (Flight Manuals,             29,500           3.245
 Operations, and Maintenance) for FRM
 Systems................................
                                         -------------------------------
    Total...............................         465,400          51.194
------------------------------------------------------------------------

    As these recordkeeping costs will be spread out evenly over the
three years, the yearly burden will be $17.065 million and involve
155,133 hours.
    After this initial 3-year period, this rulemaking would result in
an annual recordkeeping and reporting burden of 4,000 hours. This
burden is based on five (5) design approval holders submitting 40 total
reports per year requiring an average of 100 hours to complete each
report. All records that will be generated to verify the installation,
to record any fuel tank system inerting failures, and to record any
maintenance would use forms currently required by the FAA.
    The FAA computed the annual recordkeeping (Total Pages) burden by
analyzing the necessary paperwork requirements needed to satisfy each
process of the rule.
    An agency may not collect or sponsor the collection of information,
nor may it impose an information collection requirement unless it
displays a currently valid Office of Management and Budget (OMB)
control number.

International Compatibility

    In keeping with U.S. obligations under the Convention on
International Civil Aviation, it is FAA policy to comply with
International Civil Aviation Organization (ICAO) Standards and
Recommended Practices to the maximum extent practicable. The FAA has
determined that there are no ICAO Standards and Recommended Practices
that correspond to these proposed regulations.

Regulatory Evaluation Summary

Regulatory Evaluation, Regulatory Flexibility Determination,
International Trade Assessment, and Unfunded Mandates Assessment

    Changes to Federal regulations must undergo several economic
analyses. First, Executive Order 12866 directs that each Federal agency
shall propose or adopt a regulation only upon a reasoned determination
that the benefits of the intended regulation justify its costs. Second,
the Regulatory Flexibility Act of 1980 (Pub. L. 96-354) requires
agencies to analyze the economic impact of regulatory changes on small
entities. Third, the Trade Agreements Act (Pub. L. 96-39) prohibits
agencies from setting standards that create unnecessary obstacles to
the foreign commerce of the United States. In developing U.S.
standards, this Trade

[[Page 42483]]

Act requires agencies to consider international standards and, where
appropriate, that they be the basis of U.S. standards. Fourth, the
Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4) requires agencies
to prepare a written assessment of the costs, benefits, and other
effects of proposed or final rules that include a Federal mandate
likely to result in the expenditure by State, local, or tribal
governments, in the aggregate, or by the private sector, of $100
million or more annually (adjusted for inflation with base year of
1995). This portion of the preamble summarizes the FAA's analysis of
the economic impacts of this final rule. We suggest readers seeking
greater detail read the full regulatory evaluation, a copy of which we
have placed in the docket for this rulemaking.
    In conducting these analyses, the FAA has determined that this
final rule: (1) Has benefits that justify its costs, (2) is an
economically ``significant regulatory action'' as defined in section
3(f) of Executive Order 12866, (3) is ``significant'' as defined in
DOT's Regulatory Policies and Procedures; (4) will have a significant
economic impact on a substantial number of small entities; (5) will not
create unnecessary obstacles to the foreign commerce of the United
States; and (6) will impose an unfunded mandate on state, local, or
tribal governments, or on the private sector by exceeding the
previously identified threshold. These analyses are summarized as
follows.
Aviation Industry Affected
    The rule affects Boeing, Airbus, and operators of certain Boeing
and Airbus airplanes that have heated center wing tanks (HCWTs).\31\
---------------------------------------------------------------------------

    \31\ The following airplane models are not included as HCWT
airplanes: B-717; B-727; certain B-767 and B-777 models, A-321, A-
330-200 and A380. In addition, the B-787 is not included because it
needs FRM to comply with its existing Part 25 certification
requirements.
---------------------------------------------------------------------------

Disposition of Comments
    There were many comments on the Initial Regulatory Evaluation (IRE)
associated with FRM. We accepted many of these comments. However, the
volume and the technical nature of these comments require a more
detailed response than is possible in this summary. As a result, the
complete disposition of the economic comments and their effects on the
economic analysis are contained in the complete Final Regulatory
Evaluation, which is filed separately.
Period of Analysis and Affected Airplanes
    The period of analysis begins in 2008 and concludes in 2042. We
used a 10-year time period (2008-2017) to calculate the equipment
installation costs for airplanes affected by the final rule. The end of
the analysis period of 2042 captures the full operative lives of the
2009-2017 production airplanes.
    The airplanes affected by the final rule include passenger
airplanes with HCWTs manufactured prior to the 2009 production cut-in
date. These airplanes will need to be retrofitted with FRM by 2017. In
addition, these affected airplanes also include all production
passenger and cargo airplanes with HCWTs that will be manufactured
between 2009 and 2017 (except the B-787 and A380 that will be
manufactured with FRM. Cargo airplanes manufactured before 2009 and
cargo airplanes that have been or will be converted from passenger
airplanes (conversion cargo airplanes) are not included unless FRM was
installed while the airplane was used in passenger service.
    Airplanes have an average 25-year life expectancy. Thus, the 2009
production airplanes will be retired in 2033 and the last of the
production airplanes in this analysis (those produced in 2017) will be
out of service by 2042. Similarly, all of the pre-2009 existing
airplanes requiring retrofitting will be retired by 2033 (the 2008
production airplanes will be the last year of production airplanes will
not have FRM installed as original equipment). Thus, the maintenance
and fuel costs will begin in 2009 and continue to 2042 for production
airplanes and will begin in 2010 and continue to 2033 for retrofitted
airplanes.
    During the analysis period the final rule will affect an estimated
5,110 airplanes, 5,022 retrofitted and production passenger airplanes
(2,732 retrofitted and 2,290 production) and 88 production cargo
airplanes (see Table 1). These airplanes will fly 370 million hours,
364 million for passenger airplanes and 6 million for production cargo.
Of the 364 million passenger airplane flight hours, 303 million will be
flown by airplanes with FRM and 61 million will be flown by airplanes
without FRM. The airplanes without FRM will be those manufactured prior
to 2009 until they are retired or retrofitted between 2008 and 2017.

  Table 1.--Summary of the Total Numbers of Airplanes and Flight Hours
                          Affected by the Rule
------------------------------------------------------------------------
                                                           Flight hours
            Airplane category                Airplanes      (millions)
------------------------------------------------------------------------
PASSENGER PRODUCTION....................           2,290             199
RETROFITTED WITH FRM....................           2,732             105
NO FRM..................................  ..............              61
                                         -------------------------------
    TOTAL PASSENGER.....................           5,022             364
CARGO PRODUCTION........................              88               6
                                         -------------------------------
    TOTAL...............................           5,110             370
------------------------------------------------------------------------

Risk of a HCWT Explosion
    If there were no final rule and no SFAR 88, engineering analysis
indicates that there would be 1 explosion for every 100 million HCWT
airplane flight hours. Air carrier passenger airplanes would incur 3.64
explosions of which production airplanes would incur 1.99 explosions
and retrofitted airplanes would incur 1.65 explosions. Of the
retrofitted airplanes, 1.04 would occur to airplanes with FRM and 0.61
would occur to airplanes without FRM. Production cargo airplanes would
incur 0.06 explosions. As, obviously, fractions of accidents do not
occur, we describe the cumulative probability of the number of
accidents in fractions of an accident for analytic purposes. For
example, engineering analysis would project that the first accident
would occur in 2012, the second one in 2019, the third one in 2026, and
the final 0.64 of an accident in 2035. However, care

[[Page 42484]]

should be taken in assuming that these rare events will necessarily
occur in the forecasted year. As an illustration, in a 1,000 Monte
Carlo simulation trials, 3 accidents occurred 233 times out of the 1000
trials. For those 3-accident cases, two accidents happened in the same
year 25 times.
Number of HCWT Explosions Potentially Affected by the Rule
    Our Monte Carlo analysis indicates that we cannot statistically
reject the hypothesis that SFAR 88 is 50 percent effective in
preventing these accidents. This analysis, in combination with the
service history since the implementation of SFAR 88, indicates that a
50 percent SFAR 88 effectiveness rate is appropriate, but we conducted
a sensitivity analysis using two other possible SFAR 88 effectiveness
rates of 25 percent and 75 percent in the Final Regulatory Evaluation.
Using a 50 percent SFAR 88 effectiveness rate, in the absence of this
final rule, we calculate that there would be 1.82 HCWT air carrier
passenger airplane explosions occurring to the HCWT airplanes during
the time period of the analysis. As it will take time to install FRM,
77 percent of the flight hours will be flown by airplanes with FRM
while 23 percent of the flight hours will be flown by airplanes without
FRM. Thus, 1.52 air carrier passenger airplane HCWT explosions will be
prevented by the rule and 0.3 HCWT explosions could occur to airplanes
without FRM.
Percentage of In-Flight Explosions
    Our engineering analysis determined that eighty percent of the
accidents would occur in flight and twenty percent would occur on the
ground.
Benefits
    There are two types of benefits from preventing an airplane
explosion. Direct safety benefits arise from preventing the resulting
fatalities and property losses. Secondly, demand benefits arise from
preventing the aviation demand losses resulting from the reduction in
demand to fly, which will be a consequence of a loss of public
confidence in commercial aviation safety following an airplane
explosion. Further, the explosion that results from an electrical
charge is indistinguishable (until the accident is investigated) from
an explosion caused by a terrorist bomb. This uncertainty about the
explosion cause may result in costly governmental and industry
reactions to a perceived terrorist plot. However, the benefits
preventing such a potential reaction is too speculative to provide a
definitive quantitative benefit estimate, although we have quantified a
possible estimate in Appendix A of the Regulatory Evaluation.
Quantified Demand Benefits
    As discussed in the economic literature, there is a direct,
immediate, but temporary decrease in air travel in the aftermath of a
catastrophic air carrier passenger airplane explosion. We estimate the
loss to the aviation industry to be $292 million from such an accident.
Quantified Direct Benefits
Direct Benefits From Preventing a HCWT Explosion--Assumptions and
Values
     Final rule is published on January 1, 2008.
     Discount rate is 7 percent.
     Passenger airplanes would be retrofitted between 2010 and
2017.
     No airplane scheduled to be retired before 2018 will be
retrofitted.
     Passenger airplanes have a 25-year service life.
     With no SFAR 88 and no FRM rule, a heated center wing tank
(HCWT) airplane will have a fuel tank explosion every 100 million
flight hours.
     Special Federal Air Regulation (SFAR) 88 will prevent half
of the future explosions.
     Boeing and Airbus HCWT airplanes have equal explosion
risks.
     80 percent of the accidents will be catastrophic in-flight
accidents; with an average of 142 fatalities for a passenger airplane
and 2 fatalities for a cargo airplane.
     20 percent of the accidents will occur on-the-ground with
an average of 14 fatalities for a passenger airplane and no fatalities
for a cargo airplane.
     The airplane is destroyed in an HCWT explosion.
     The value of a prevented fatality is $5.5 million.
Direct Benefits From Preventing a HCWT Explosion--Results
     The average undiscounted direct benefits from preventing
an air carrier passenger airplane in-flight HCWT explosion will be $841
million, with a range of $628 million to $2.2 billion.
     The average undiscounted direct benefits from preventing
an air carrier passenger airplane on-the-ground HCWT explosion will be
$115 million, with a range of $77 million to $320 million.
     The average undiscounted direct benefits from preventing
an air carrier passenger airplane HCWT explosion weighted by an 80
percent probability of an in-flight accident and a 20 percent
probability of an on-the-ground accident will be $696 million.
     The average undiscounted direct benefits from preventing
an air carrier cargo airplane HCWT explosion will be $77 million.
Total Benefits
    Of great concern to the FAA is that a practical solution now exists
for a real threat of an aviation catastrophe. Even though these are low
probability accidents, they are high consequence accidents. For
example, if a single in-flight catastrophic accident with 190 occupants
(235 seats) is prevented by 2012, the present value of the benefits
will be greater than the present value of the costs. Using a $5.5
million value for a prevented fatality, the benefits from preventing an
in-flight explosion range of $625 million to $750 million for a B-737
or an A-320 family airplane to $1.0 billion to $2.15 billion for all
other affected airplanes. The mean of the estimated benefits from
preventing an in-flight explosion (weighted by the number of flight
hours for each type of affected airplane model) are $840 million.
    Thus, the undiscounted total weighted average benefit from
preventing an in-flight explosion is $1.130 billion. Adjusting this
value for the 20 percent of the accidents that will occur on the ground
produces an undiscounted average benefit of about $1 billion.
    We calculated that the present value of the weighted average
benefits from preventing the 1.5 accidents would be $657 million.
Compliance Cost Assumptions and Values
    The compliance costs are based on installing a fuel tank inerting
(FTI) system because that is the only FRM system that has been
developed. If a future FRM system is developed that competes with FTI
then we have likely overestimated the compliance costs.
     Fully burdened aviation engineer labor rate is $110 an
hour.
     Fully burdened aviation mechanic labor rate is $80 an
hour.
     One-time engineering costs to develop STCs or modified TCs
are between $2.2 million to $5.7 million a model.
     Retrofitting kits cost from $77,000 (B-737 and A-320
Family), $120,000-$164,000 (B-757, B-767, and A-300/310), to $165,000-
$192,000 (all other airplanes).
     Initial retrofitting labor costs in 2010 will range from
$24,000 to $70,000.

[[Page 42485]]

     There is a retrofitting labor learning curve of 30 percent
such that the retrofitting labor hours (and costs) will be
approximately 70 percent of the 2010 labor hours in 2013 and 49 percent
of the 2010 labor hours by 2017.
     Retrofitting kit and labor costs in 2010 will range from
$100,000 for the B-737 and A-320 Family and $148,000 to $203,000 (for
all other airplanes).
     Out-of-Service Losses (Associated with a retrofit during a
routine ``D'' check) are $10,000 to $28,000.
     Out-of-Service Losses (Associated with a retrofit during a
special maintenance session) are $30,000 to $84,000.
     The same reduction in hours out-of-service for labor hours
will apply to the number of out-of-service hours.
     Retrofitting kits weigh 84 pounds (for the B-737 and the
A-320 family), 117 pounds to 150 pounds (for the B-757, B-767, and A-
300/310), and 182 pounds to 215 pounds for the B-747, B-777, and A-330/
340).
     Retrofitted airplane increased annual fuel burn from
weight, bleed air intake, and ram drag is 2,000-2,500 gallons (B-737)
to 4,000 gallons (A-320 Family) to 4,400 to 6,500 gallons (everything
else).
     Production airplane FTI kit costs are $92,000 (B-737 and
A-320) to $186,000-$205,000 (for all other airplanes).
     Production airplane labor installation costs are $6,500-
$8,000.
     Production kit and labor costs in 2009 will be $100,000
for the B-737 and A-320 Family) and $195,000 to $212,500 (for all other
airplanes).
     Production airplane FTI weight is 105 pounds (B-737 and A-
30 Family) to 250-300 pounds (for all other airplanes).
     Production airplane increased annual fuel burn from
weight, bleed air intake, and ram drag is 2,900 gallons (B-737) to
4,600 gallons (A-320 Family) to 6,300 to 7,100 gallons (everything
else).
     Cost of aviation fuel is $2.01 per gallon.
     Additional scheduled and unscheduled maintenance, delays,
and water separator/filter replacement costs are $3,250 to $5,150.
     Annual operating costs are between $10,000 (B-737) to
$15,000 (A-320 Family) to $17,500-$20,000 (for all other airplanes).
     Air separation module (ASM) replaced every 27,000 flight
hours.
     ASM replacement cost is $45,000 (B-737 and A-320 Family)
to $135,000-$153,000 (for all other airplanes).
    Weighted average compliance costs (excluding the engineering costs)
are:
    Retrofitted Passenger Airplanes: $213,000 ($135,000 for retrofit
and $78,000 for operational). Range: $144,000 to $395,000.
    Production Passenger Airplanes: $177,000 ($68,000 for installation
and $109,000 for operational). Range: $156,000 to 410,000.
Total Compliance Costs
    As shown in Table 2, the present value of the total compliance
costs is $1.012 billion, of which $975 million will be incurred by air
carrier passenger airplane operators, and $37 million will be incurred
by air carrier production cargo airplanes.
    Of the air carrier passenger airplane present value costs of $975
million, operators of retrofitted airplanes will incur $436 million (43
percent) while operators of production airplanes will incur $539
million (57 percent).

                      Table 2.--Compliance Costs by Type of Operation and Type of Airplane
                                          [In millions of 2007 dollars]
----------------------------------------------------------------------------------------------------------------
                                                                                    Total costs
                                                                 -----------------------------------------------
                            Operator                                               Present value   Present value
                                                                   Undiscounted        (7%)            (3%)
----------------------------------------------------------------------------------------------------------------
AIR CARRIER PASSENGER:
    RETROFITTED.................................................            $839            $436            $623
    PRODUCTION..................................................           1,237             539             825
    AUXILIARY FUEL TANKS........................................              <1              <1              <1
                                                                 -----------------------------------------------
        TOTAL...................................................           2,076             975           1,448
AIR CARRIER CARGO:
    PRODUCTION..................................................             100              37              63
        TOTAL...................................................             100              37              63
                                                                 -----------------------------------------------
        GRAND TOTAL.............................................           2,176           1,012           1,511
----------------------------------------------------------------------------------------------------------------

    As shown in Table 3, 54 percent of the present value costs (at 7
percent) for retrofitted air carrier passenger airplanes are from the
engineering and one-time equipment installation costs while these costs
are 47 percent for production airplanes. Similarly, 46 percent of the
present value costs for retrofitted airplanes are due to additional
fuel, operational, and ASM (air separation module) costs while these
costs are 53 percent for production airplanes.

                         Table 3.--Compliance Costs for Air Carrier Passenger Airplanes
                                          [In millions of 2007 dollars]
----------------------------------------------------------------------------------------------------------------
                                                                                    Total costs
                                                                 -----------------------------------------------
                          Cost category                                            Present value   Present value
                                                                   Undiscounted        (7%)            (3%)
----------------------------------------------------------------------------------------------------------------
RETROFITTED:
    ENGINEERING.................................................             $19             $16             $18
    INSTALLATION................................................             346             220             283
    INVENTORY...................................................               9               6               7
    FUEL........................................................             215              93             149
    OPERATIONAL.................................................             113              49              77

[[Page 42486]]


    ASM REPLACEMENT.............................................             137              52              89
                                                                 -----------------------------------------------
        TOTAL...................................................             839             436             623
PRODUCTION:
    ENGINEERING.................................................             107             100             103
    INSTALLATION................................................             230             152             191
    INVENTORY...................................................               7               4               5
    FUEL........................................................             459             149             272
    OPERATIONAL.................................................             197              63             116
    ASM REPLACEMENT.............................................             237              71             138
                                                                 -----------------------------------------------
        TOTAL...................................................           1,237             539             825
                                                                 -----------------------------------------------
        GRAND TOTAL.............................................           2,076             975           1,448
----------------------------------------------------------------------------------------------------------------

Benefit Cost Analysis
    As previously described, these are low probability, high
consequence accidents. If a single in-flight catastrophic accident with
190 occupants (a 235 seat airplane) were to be prevented by 2012, the
present value of the benefits will be greater than the present value of
the costs. Further, as shown in the Regulatory Evaluation in Appendix
IV-7, there is a 26 percent probability that the final rule present
value benefits will be greater than its present value costs.
    As shown in Table 4, using the weighted average benefits at a 7
percent discount rate, the net benefit losses for the final rule would
be $355 million, of which production passenger airplanes would account
for $151 million, retrofitted passenger airplanes would account for
$167 million and production cargo airplanes would account for $37
million.

                             Table 4.--Present Value of the Rule Benefits and Costs
                                          [In millions of 2007 dollars]
----------------------------------------------------------------------------------------------------------------
                                                                                Present value (7%)
                        Type of operation                        -----------------------------------------------
                                                                     Benefits          Costs       Net benefits
----------------------------------------------------------------------------------------------------------------
PASSENGER:
    RETROFITTED.................................................            $271            $438          ($167)
    PRODUCTION..................................................             386             537           (151)
                                                                 -----------------------------------------------
        TOTAL...................................................             657             975           (318)
    PRODUCTION CARGO............................................              <1              37            (37)
                                                                 -----------------------------------------------
        GRAND TOTAL.............................................             657           1,012           (355)
----------------------------------------------------------------------------------------------------------------

Sensitivity Analysis of the Rule Costs and Benefits
    Table 5 provides a sensitivity analysis for the final rule that,
using the weighted by flight hours average benefit value, varies the
discount rate (7 and 3 percent), the value of preventing a statistical
fatality ($3 million, $5.5 million, and $8 million), and the SFAR 88
effectiveness rate (25, 50, and 75 percent). As is shown, the
quantified benefits are greater than the costs when the SFAR 88
effectiveness rate is 25 percent for: (1) An $8 million value of a
prevented fatality and; (2) a $5.5 million value of a prevented
fatality using a 3 percent discount rate. Net benefits numbers in
parentheses are negative.

   Table 5.--Present Values of the Benefits and Costs for all Affected Airplanes by Discount Rate, Value of a
                               Prevented Fatality, and SFAR 88 Effectiveness Rate
                                          [In millions of 2007 dollars]
----------------------------------------------------------------------------------------------------------------
                                                      SFAR 88                     Present values
          Discount rate              Value of      effectiveness -----------------------------------------------
                                     fatality        (percent)       Benefits          Costs       Net benefits
----------------------------------------------------------------------------------------------------------------
7%..............................            $5.5              50            $657          $1,012          ($355)
7%..............................               3              50             469           1,012           (543)
7%..............................               8              50             828           1,012           (184)
7%..............................             5.5              25             989           1,012            (23)
7%..............................               3              25             704           1,012           (308)

[[Page 42487]]


7%..............................               8              25           1,242           1,012             230
7%..............................             5.5              75             330           1,012           (682)
7%..............................               3              75             235           1,012           (777)
7%..............................               8              75             414           1,012           (598)
----------------------------------------------------------------------------------------------------------------
3%..............................             5.5              50           1,141           1,509           (368)
3%..............................               3              50             842           1,509           (667)
3%..............................               8              50           1,434           1,509            (75)
3%..............................             5.5              25           1,658           1,509             149
3%..............................               3              25           1,263           1,509           (246)
3%..............................               8              25           2,151           1,509             642
3%..............................             5.5              75             517           1,509           (992)
3%..............................               3              75             421           1,509         (1,088)
3%..............................               8              75             717           1,509           (792)
----------------------------------------------------------------------------------------------------------------

Differences Between the Initial Regulatory Evaluation (IRE) and Final
Regulatory Evaluation (FRE) Assumptions and Unit Values
    In the IRE, we had estimated that the present value of the proposed
rule's direct benefits would be $495 million and that the present value
of the proposed rule's costs would be $808 million. Table 6 provides a
summary of the important differences in the assumptions and the unit
values between those in the IRE and those used in this FRE. The
significant benefits increases are due to the quantification of the
demand benefits and the use of $5.5 million for the value of a
prevented fatality. In the final rule the benefits and costs were both
substantially increased by the inclusion of Boeing production airplanes
(except the B-787). In the NPRM analysis we assumed Boeing would
voluntarily comply for its production airplanes; we did not assume this
for the final rule analysis. The benefits and costs were both decreased
by the shorter period of analysis. The significant cost increases are
due to the increases in the production FTI kit costs, their annual
additional fuel consumption due to the FTI weights and the bleed air
and ram drag effects, the increased price of aviation fuel, and the air
separation module (ASM) replacement costs (there will be 1 ASM
replacement for most retrofitted airplanes and 2 ASM replacements for
most production airplanes).

                    Table 6.--Differences in the Assumptions/Values in the IRE and in the FRE
----------------------------------------------------------------------------------------------------------------
           Assumptions/values                        FRE                                 IRE
----------------------------------------------------------------------------------------------------------------
Time Period of Analysis................  2009-2042.................  2006-2055.
Accident Rate..........................  1 Every 100 Million HCWT    1 Every 60 Million HCWT Flight Hours.
                                          Flight Hours.
Number of Flight Hours.................  370 Million Total.........  460 Million.
                                         364 Million Passenger.....
                                         6 Million Production
                                          Cargo..
Number of Accidents....................  3.7 Total.................  7.67.
                                         3.64 Passenger............
                                         0.06 Cargo................
Percentage of In-Flight Accidents......  80%.......................  100%.
Base Year for Dollars..................  2007......................  2004.
Reduction in Air Travel Demand.........  $292 Million (annual real   Qualitatively large.
                                          growth rate of 3%).
Value of a Prevented Fatality..........  $5.5 Million..............  $3 Million.
Average Number of In-Flight Fatalities.  142.......................  142.
Average Number of On-the-Ground          14........................  8.
 Fatalities.
Average Accident Value for an In-Flight  $841 Million..............  $505 Million.
 Explosion (Passenger Airplane).
Average Accident Value for an On-the-    $115 Million..............  Not Estimated.
 Ground Explosion (Passenger Airplane).
Weighted Average Accident Value          $696 Million..............  $505 Million.
 (Passenger Airplane).
Weighted Average Accident Value          $77 Million...............  $75 Million.
 (Production Cargo Airplane).
Hourly Labor Rates.....................  Engineer $110.............  Engineer $115.
                                         Mechanic $80..............  Mechanic $75.
Total Number of Retrofits..............  Passenger 2,732...........  Passenger 3,328.
                                         Boeing 1,780..............  Boeing 2,327.
                                         Airbus 952................  Airbus 1,001.
Retrofitting Kit Costs.................  Small $77,000.............  Small $105,000.
                                         Medium $120,000-$164,000..  Medium $135,000.
                                         Large $175,000-$192,000...  Large $179,000.
Retrofitting Labor Costs (Scheduled      $24,000-$28,000...........  $30,000-$35,000.
 Maintenance).

[[Page 42488]]


Number of Out-of-Service Days            2.........................  2.
 (Scheduled Maintenance).
Out-of-Service Costs (Scheduled          Small $10,000.............  Small $9,000.
 Maintenance).
                                         Medium $22,000............  Medium $14,000.
                                         Large $28,000.............  Large $13,000.
Retrofitting Costs (Scheduled            Small $110,000............  Small $135,000.
 Maintenance).
                                         Medium $165,000-$215,000..  Medium $170,000.
                                         Large $214,000-$229,000...  Large $214,000.
Retrofitting Labor Costs (Dedicated      $62,000-$70,000...........  $40,000-$45,000.
 Visit).
Number of Out-of-Service Days            6.........................  4.
 (Dedicated Visit).
Out-of-Service Costs (Dedicated Visit).  Small $30,000.............  Small $19,000.
                                         Medium $66,000............  Medium $56,000.
                                         Large $84,000.............  Large $53,000.
Retrofitting Costs (Dedicated Visit)...  Small $137,000............  Small $163,000.
                                         Medium $211,000-$264,000..  Medium $234,000.
                                         Large $289,000-$311,000...  Large $276,000.
Fuel Cost per Gallon...................  $2.01.....................  $1.00.
Retrofitting FTI Weight................  Small 84 lbs..............  Small 95 lbs.
                                         Medium 117-150 lbs........  Medium 148 lbs.
                                         Large 182-215 lbs.........  Large 218 lbs.
Annual Retrofitted Passenger Airplane    Small 2,500-4,000 Gals....  Small 1,500-3,900.
 Fuel Consumption (Weight, Bleed Air,
 and Ram Drag).
                                         Medium 3,000-4,125 Gals...  Medium 2,900.
                                         Large 4,500-6,550 Gals....  Large 4,800.
Annual Retrofitted Passenger Airplane    Small $5,250-$8,000.......  Small $1,500-$3,900.
 Fuel Cost.
                                         Medium $6,000-$8,300......  Medium $2,900.
                                         Large $9,000-$13,150......  Large $4,800.
Total Number of Production Passenger     Total 2,290 (2009-2017)...  Total 3,274 (2008-2030).
 Airplanes.
                                         Boeing 1,268..............  Boeing 0.
                                         Airbus 1,022..............  Airbus 2,650.
Total Number of Production (No           Total 88 (2009-2017)......  Total 624 (2008-2030).
 Conversion) Cargo Airplanes.
                                         Boeing 66.................  Boeing 0.
                                         Airbus 22.................  Airbus 624 (includes Conversion).
Production Kit Costs...................  Small $92,000.............  Small $83,000.
                                         Medium $186,000...........  Medium $107,000.
                                         Large $205,000............  Large $137,000.
Production Labor Costs.................  $6,500-$8.000.............  $7,000-$8.000.
Unit Production Costs..................  Small $98,000.............  Small $90,000.
                                         Medium $194,000...........  Medium $115,000.
                                         Large $213,000............  Large $145,000.
Production FTI Weight..................  Small 105 lbs.............  Small 95 lbs.
                                         Medium 280 lbs............  Medium 148 lbs.
                                         Large 300 lbs.............  Large 218 lbs.
Annual Production Passenger Airplane     Small 2,300-4,625 Gals....  Small 1,500-3,900.
 Fuel Consumption (Weight, Bleed Air,
 and Ram Drag).
                                         Medium 5,600-6,725 Gals...  Medium 2,900.
                                         Large 6,850-8,600 Gals....  Large 4,800.
Annual Production Passenger Airplane     Small $3,850-$7,625.......  Small $1,500-$3,900.
 Fuel Cost.
                                         Medium $9,250-$11,100.....  Medium $2,900.
                                         Large $11,300-$14,300.....  Large $4,800.
Maintenance............................  $3,250-$5,150.............  $5,900-$7,500.
ASM Replacement Cost (Every 9 Years)...  Small $30,500-$45,000.....  Small $5,275.
                                         Medium $135,000...........  Medium $18,761.
                                         Large $153,000............  Large $28,814.
----------------------------------------------------------------------------------------------------------------

Costs and Benefits of Alternatives to the Final Rule
    As shown in Table 7, we evaluated the baseline costs and weighted
average benefits for the 8 alternatives to the final rule using a value
of $5.5 million for a prevented fatality, a 7 percent discount rate,
and a 50 percent SFAR 88 effectiveness rate. These expected benefits
are based on a rare event mean probability. The date when an avoided
accident occurs has a significant impact on the expected benefits.

ALTERNATIVE 1. Cover only air carrier passenger airplanes
ALTERNATIVE 2. Exclude auxiliary fuel tanks
ALTERNATIVE 3. Cover only air carrier retrofitted passenger airplanes
ALTERNATIVE 4. Cover only air carrier production passenger airplanes
ALTERNATIVE 5. Cover only air carrier production passenger and cargo
airplanes
ALTERNATIVE 6. Final rule plus part 91 airplanes
ALTERNATIVE 7. Final rule plus conversion cargo airplanes
ALTERNATIVE 8. Final rule plus conversion and retrofitted cargo
airplanes

[[Page 42489]]



  Table 7.--Benefits and Cost Summaries for 8 Alternatives to the Final
  Rule Using a $5.5 Million Value for a Prevented Fatality, a 7 Percent
       Discount Rate, and a 50 Percent SFAR 88 Effectiveness Rate
                      [In millions of 2007 dollars]
------------------------------------------------------------------------
                                      Present value (7%)
              Option              --------------------------     Net
                                     Benefits      Costs       benefits
------------------------------------------------------------------------
FINAL RULE.......................         $657       $1,012       ($355)
ALTERNATIVES:
    1. Cover Only Part 121                 657          975        (318)
     Passenger Airplanes
     (excludes Part 121 cargo and
     Part 91)....................
    2. Cover Only Part 121                 657          975        (318)
     Passenger Airplanes but No
     Auxiliary Tanks.............
    3. Cover Only Part 121                 271          438        (167)
     Retrofitted Passenger
     Airplanes (excludes All
     Production Passenger, all
     Cargo, and Part 91
     Airplanes)..................
    4. Cover Only Part 121                 386          537        (151)
     Production Passenger
     Airplanes...................
    5. Cover Only Part 121                 386          574        (188)
     Production Passenger and
     Cargo Airplanes.............
    6. Final Rule Plus Part 91             657        1,026        (369)
     Airplanes...................
    7. Final Rule Plus Conversion          657        1,109        (452)
     Cargo Airplanes.............
    8. Final Rule Plus Conversion          657        1,229        (572)
     and Retrofitted Cargo
     Airplanes...................
------------------------------------------------------------------------

    Another way to analyze these alternatives is to evaluate them on an
incremental cost per life saved; i.e., a cost-effectiveness analysis.
For this rule, the effectiveness metric is the number of expected
prevented fuel tank explosions, which is then converted into the
present value of the number of fatalities prevented. The mid-point of
the time-frame in which an accident would happen is 2022 for production
airplanes and 2019 for retrofitted airplanes. For all other airplanes,
the mid-point would be about 50 years from today, or 2060. In Table 8,
the first column lists the specific types of airplanes that could have
FRM installed. The second column reports the number of fuel tank
explosions that FRM would prevent using an SFAR 88 effectiveness rate
of 50 percent. The third column provides the present value of the total
costs to install FRM on those airplanes minus the present value of the
destroyed airplane and minus the demand benefits weighted by the number
of flight hours. The passenger airplane hull value is $50, which gives
present values of $19 million for production airplanes and $24 million
for retrofitted airplanes. The present value of the demand benefits
would be $100 million for retrofitted airplanes and $151 million for
production airplanes. The fourth column takes the number of prevented
explosions and divides it into the costs to calculate the present value
of the cost to prevent one explosion. The fifth column provides the
number of fatalities that would be prevented if FRM were installed on
the airplane assuming that 80 percent of the explosions would be in-
flight and 20 percent would be on the ground. These numbers are then
adjusted by the discount rate to reflect the present value of the
fatalities for production and retrofitted passenger airplanes. The
final column supplies the average present value of the cost for that
option to prevent one fatality. As shown in Table 8, the two most cost-
effective options would be to install FRM on production passenger
airplanes and on existing passenger airplanes. The final rule contains
all of the options except conversion cargo airplanes and retrofitted
cargo airplanes.

 Table 8.--Incremental Cost Effectiveness Analysis of the Individual Alternatives Using a Present Value Analysis
                   With a 7 Percent Discount Rate and a 50 Percent SFAR 88 Effectiveness Rate
                                    [Total costs in millions of 2007 dollars]
----------------------------------------------------------------------------------------------------------------
                                                       PV           PV                              PV
                                      Number of  -------------------------- Average No. ------------------------
              Options                 explosions  Costs--hull    Cost to         of
                                      prevented    and demand  prevent one   fatalities     Cost to prevent 1
                                                      loss       accident                  statistical fatality
----------------------------------------------------------------------------------------------------------------
Production Passenger Airplanes.....         1.00         $367         $367           46                   $8.000
Production Cargo Airplanes.........       0.0385           37          961         .055               17,473.000
Production Part 91 Airplanes.......      0.00082            2        2,439         .249                9,785.000
Retrofitted Passenger Airplanes....         0.52          314          604           56                   11.000
Conversion Cargo Airplanes.........        0.095           83          874         .055               15,891.000
Retrofitted Cargo Airplanes........        0.064          110        1,719         .055               31,255.000
Retrofitted Part 91 Airplanes......       0.0194           12        6,186         .249               24,843.000
Final Rule.........................       1.5585          741          475           49                   10.000
----------------------------------------------------------------------------------------------------------------

Conclusion
    When modeling discrete rare events such as fuel tank explosions, it
is important to understand and evaluate the distribution around the
mean value rather than to rely only on a single point estimated value.
This variability analysis indicates there is a substantial (23 percent)
probability that the quantified benefits will be greater than the
costs.
    The Federal Aviation Administration believes that the correct
public policy choice is to eliminate the substantial probability of a
high consequence fuel tank explosion accident by proceeding with the
final rule.
Regulatory Flexibility Analysis
Introduction and Purpose of This Analysis
    The Regulatory Flexibility Act of 1980 (Pub. L. 96-354) (RFA)
establishes ``as a principle of regulatory issuance that agencies shall
endeavor, consistent with the objectives of the rule and of

[[Page 42490]]

applicable statutes, to fit regulatory and informational requirements
to the scale of the businesses, organizations, and governmental
jurisdictions subject to regulation. To achieve this principle,
agencies are required to solicit and consider flexible regulatory
proposals and to explain the rationale for their actions to assure that
such proposals are given serious consideration.'' The RFA covers a
wide-range of small entities, including small businesses, not-for-
profit organizations, and small governmental jurisdictions.
    Agencies must perform a review to determine whether a rule will
have a significant economic impact on a substantial number of small
entities. If the agency determines that it will, the agency must
prepare a regulatory flexibility analysis as described in the RFA.
    We believe that this final rule will have a significant economic
impact on a substantial number of small entities. The purpose of this
analysis is to provide the reasoning underlying the FAA determination.
The FAA has determined that:

--There will not be a significant impact on a substantial number of
manufacturers.
--There will be a significant impact on a substantial number of small
operators.

    To make this determination in this final rule, we perform a
Regulatory Flexibility Analysis (RFA). Under Section 63(b) of the RFA,
the analysis must address:

--Description of reasons the agency is considering the action.
--Statement of the legal basis and objectives for the rule.
--Significant issues raised during public comment.
--Description of the recordkeeping and other compliance requirements of
the rule.
--All federal rules that may duplicate, overlap, or conflict with the
rule.
--Description and an estimated number of small entities.
--Economic impact.
--Describe the alternatives considered.
Description of Reasons the Agency Is Considering the Action
    Fuel tank explosions have been a threat with serious aviation
safety implications for many years. The explosion of TWA Flight 800 (a
Boeing 747) off Long Island, New York in 1996 occurred in-flight with
the loss of all 230 on board. Two other explosions on airplanes
operated by Philippine Airlines and Thai Airlines occurred on the
ground (resulting in nine fatalities). While the accident
investigations of the TWA, Philippine Airlines, and Thai Airlines
accidents failed to identify the ignition source that caused the
explosion, the investigations found several similarities
    The requirements contained in this final rule will reduce the
likelihood of fuel tank fires, and mitigate the effects of a fire if
one occurs.
Statement of the Legal Basis and Objectives for the Rule
    The FAA's authority to issue rules regarding aviation safety is
found in Title 49 of the United States Code. Subtitle I, Section 106
describes the authority of the FAA Administrator. Subtitle VII,
Aviation Programs, describes in more detail the scope of the agency's
authority.
    This rulemaking is promulgated under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701, ``General
requirements.'' Under that section, the FAA is charged with promoting
safe flight of civil aircraft in air commerce by prescribing minimum
standards required in the interest of safety for the design and
performance of aircraft; regulations and minimum standards in the
interest of aviation safety for inspecting, servicing, and overhauling
aircraft; and regulations for other practices, methods, and procedures
the Administrator finds necessary for safety in air commerce. This
regulation is within the scope of that authority because it prescribes:
     New safety standards for the design of transport category
airplanes, and
     New requirements necessary for safety for the design,
production, operation and maintenance of those airplanes, and for other
practices, methods, and procedures related to those airplanes.
    Accordingly, this final rule amends Title 14 of the Code of Federal
Regulations and address deficiencies in current regulations regarding
airplane designs of the current and future fleet. The rule will require
transport category airplanes to minimize flammability of fuel tanks.
Significant Issues Raised During Public Comment
    Individuals and companies commented that they will incur costs as a
result of the requirements contained in the rule. The National Air
Carrier Association (NACA) supports FRM being applied to production
passenger airplanes. They oppose applying FRM to existing passenger
airplanes and to any cargo airplanes. Their primary concerns were that
the cost of retrofitting passenger airplanes was too high for the
potential benefits and they believe that cargo airplanes were not at
risk. They did not provide specific cost estimates. The Regional
Airline Association (RAA) opposes any FRM requirement, although only
one of their member airlines has airplanes that will be affected by the
final rule.
Description of the Recordkeeping and Other Compliance Requirements of
the Rule
    We expect no more than minimal new reporting and recordkeeping
compliant requirements to result from this rule. The rule will require
additional entries in existing required maintenance records to account
for either the additional maintenance requirements or the installation
of nitrogen-inerting systems and the addition of insulation between
heat-generating equipment and fuel tanks.
All Federal Rules That May Duplicate, Overlap, or Conflict With the
Rule
    SFAR 88 was enacted to ensure no ignition sources exist in the fuel
tanks. After that rule was promulgated and the manufacturers' safety
analyses were submitted to the regulatory authorities, we continued to
find ignition sources that had not been revealed in the safety
analyses. Thus, SFAR 88 cannot eliminate all future ignition sources.
This rule is designed to work in conjunction with SFAR 88 to prevent
future HCWT explosions. We are unaware that the rule will overlap,
duplicate or conflict with any other existing Federal Rules.
Description and an Estimated Number of Small Entities
    The FAA uses the size standards from the Small Business
Administration for Air Transportation and Aircraft Manufacturing
specifying companies having less than 1,500 employees as small
entities. Boeing is the sole U.S. manufacturer affected by this final
rule. As Boeing has more than 1,500 employees and is not considered a
small entity, there will not be a significant impact on a substantial
number of manufacturers.
    We identified a total of 15 U.S. operators who will be affected by
this final rule and qualify as small businesses because they have fewer
than 1,500 employees. These 15 entities operate a total of 214
airplanes. Once the firms were classified as small entities, we
gathered information on their annual revenues.
    We obtained the small entities' fleets using data from FAA Flight
Standards and BACK Associates Fleet Database. The number of employees
and revenues

[[Page 42491]]

were obtained from the U.S. Department of Transportation Form 41
filings, BTS Office of Airline Information, Hoovers Online, and Thomas
Gale Business and Company Resource Center.
Economic Impact
    To assess the cost impact to small business part 121 airlines, we
estimated the present value retrofit cost for the affected aircraft in
the small entities fleet. Table 8 summarizes the cost to retrofit per
airplane and the associated model types.

                Table 8.--Retrofit Cost by Airplane Model
------------------------------------------------------------------------
                                                               Present
                           Model                              value cost
------------------------------------------------------------------------
Retrofit Cost Per Model:
    B-737-Classic..........................................     $137,000
    B-737-NG...............................................      121,000
    B-757..................................................      211,000
    B-767..................................................      264,000
    B747-100/100/300.......................................      289,000
    B-747-400..............................................      289,000
    B-777..................................................      311,000
    A-320 Family...........................................      137,000
    A-330..................................................      311,000
------------------------------------------------------------------------

    We estimated each operator's compliance cost by multiplying the
average retrofit cost per airplane by the total number of each type of
airplane the operator currently has. Then we measured the economic
impact on small entities by dividing the firms' total estimated present
value compliance cost by its annual revenue. We believe that if the
retrofit cost exceeds 2% of a firm's annual revenue, then there is a
significant economic impact. As shown in the following table, the
present value of the retrofitting costs is estimated to be greater than
two percent of annual revenues for three small operators. Thus, as the
rule will have a significant economic impact on three small operators
we determined this final rule will have a significant impact on a
substantial number of small entities.

   Table 9.--Total Retrofitting Costs and Their Percentage of Annual Revenues for the Affected Small Operators
----------------------------------------------------------------------------------------------------------------
                                                         Number of                                    Cost as a
          Airplane model               Small entity       affected       Cost       Annual revenue    percent of
                                         operator         aircraft                                     revenue
----------------------------------------------------------------------------------------------------------------
BOEING 737-700...................  ALOHA AIRLINES.....            2     $242,000  .................  ...........
BOEING 737-700...................  ALOHA AIRLINES.....            5      605,000  .................  ...........
BOEING 737-700...................  ALOHA AIRLINES.....            1      121,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........      968,000       $300,601,582         0.32
                                                                    ============================================
BOEING 737-300...................  ATA AIRLINES.......            3      411,000  .................  ...........
BOEING 737-800...................  ATA AIRLINES.......           11    1,331,000  .................  ...........
BOEING 737-800...................  ATA AIRLINES.......            1      121,000  .................  ...........
BOEING 757-200...................  ATA AIRLINES.......            4    1,055,000  .................  ...........
BOEING 757-200...................  ATA AIRLINES.......            2      422,000  .................  ...........
BOEING 757-300...................  ATA AIRLINES.......            4      844,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........    4,184,000        330,177,135         1.27
                                                                    ============================================
BOEING 757-200...................  EOS AIRLINES.......            3      633,000          1,084,907       58.350
AIRBUS A318-100..................  FRONTIER AIRLINES              8    1,096,000  .................  ...........
                                    [CO-USA].
AIRBUS A319-100..................  FRONTIER AIRLINES             39    5,343,000  .................  ...........
                                    [CO-USA].
AIRBUS A319-100..................  FRONTIER AIRLINES             10    1,370,000  .................  ...........
                                    [CO-USA].
                                                                    --------------------------------------------
    Total........................  ...................  ...........    7,809,000      1,130,837,682         0.69
                                                                    ============================================
BOEING 767-300...................  HAWAIIAN AIRLINES..            4    1,056,000  .................  ...........
BOEING 767-300...................  HAWAIIAN AIRLINES..            8    2,112,000  .................  ...........
BOEING 767-300...................  HAWAIIAN AIRLINES..            3      792,000  .................  ...........
BOEING 767-300...................  HAWAIIAN AIRLINES..            3      792,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........    4,752,000        881,599,398         0.54
                                                                    ============================================
BOEING 767-200...................  MAXJET AIRWAYS.....            1      264,000  .................  ...........
BOEING 767-200...................  MAXJET AIRWAYS.....            1      264,000  .................  ...........
BOEING 767-200...................  MAXJET AIRWAYS.....            1      264,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........      792,000          2,422,199        32.70
                                                                    ============================================
BOEING 737-400...................  MIAMI AIR                      2      274,000  .................  ...........
                                    INTERNATIONAL.
BOEING 737-800...................  MIAMI AIR                      3      363,000  .................  ...........
                                    INTERNATIONAL.
BOEING 737-800...................  MIAMI AIR                      1      121,000  .................  ...........
                                    INTERNATIONAL.
BOEING 737-800...................  MIAMI AIR                      1      121,000  .................  ...........
                                    INTERNATIONAL.
BOEING 737-800...................  MIAMI AIR                      2      121,000  .................  ...........
                                    INTERNATIONAL.
                                                                    --------------------------------------------
    Total........................  ...................  ...........    1,000,000         73,403,477         1.36
                                                                    ============================================
BOEING 757-200...................  PRIMARIS AIRLINES..            1      211,000         19,403,658         1.09
BOEING 737-300...................  RYAN INTERNATIONAL             1      137,000  .................  ...........
                                    AIRLINES.
BOEING 737-400...................  RYAN INTERNATIONAL             1      137,000  .................  ...........
                                    AIRLINES.
BOEING 737-800...................  RYAN INTERNATIONAL             2      242,000  .................  ...........
                                    AIRLINES.
BOEING 737-800...................  RYAN INTERNATIONAL             1      121,000  .................  ...........
                                    AIRLINES.

[[Page 42492]]


BOEING 737-800...................  RYAN INTERNATIONAL             1      121,000  .................  ...........
                                    AIRLINES.
BOEING 757-200...................  RYAN INTERNATIONAL             1      211,000  .................  ...........
                                    AIRLINES.
BOEING 757-200...................  RYAN INTERNATIONAL             1      211,000  .................  ...........
                                    AIRLINES.
BOEING 757-200...................  RYAN INTERNATIONAL             2      422,000  .................  ...........
                                    AIRLINES.
                                                                    --------------------------------------------
    Total........................  ...................  ...........    1,602,000        101,560,750         1.58
                                                                    ============================================
AIRBUS A319-100..................  SPIRIT AIRLINES               30    4,100,000  .................  ...........
                                    [USA].
AIRBUS A321-100..................  SPIRIT AIRLINES                6      822,000  .................  ...........
                                    [USA].
                                                                    --------------------------------------------
    Total........................  ...................  ...........    4,922,000        540,426,363         0.91
                                                                    ============================================
BOEING 737-800...................  SUN COUNTRY                    2      242,000  .................  ...........
                                    AIRLINES.
BOEING 737-800...................  SUN COUNTRY                    6      726,000  .................  ...........
                                    AIRLINES.
BOEING 737-800...................  SUN COUNTRY                    2      242,000  .................  ...........
                                    AIRLINES.
BOEING 737-800...................  SUN COUNTRY                    3      363,000  .................  ...........
                                    AIRLINES.
                                                                    --------------------------------------------
    Total........................  ...................  ...........    1,573,000        225,789,595         0.70
                                                                    ============================================
AIRBUS A320-100..................  USA 3000 AIRLINES..            1      137,000  .................  ...........
AIRBUS A320-100..................  USA 3000 AIRLINES..            1      137,000  .................  ...........
AIRBUS A320-100..................  USA 3000 AIRLINES..            9    1,233,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........    1,507,000        132,077,603         1.14
                                                                    ============================================
B-737-429........................  CASINO EXPRESS.....            1      137,000  .................  ...........
B-737-46B........................  CASINO EXPRESS.....            1      137,000  .................  ...........
B-737-4S3........................  CASINO EXPRESS.....            1      137,000  .................  ...........
B-737-8Q8........................  CASINO EXPRESS.....            2      242,000  .................  ...........
B-737-8Q8........................  CASINO EXPRESS.....            1      121,000  .................  ...........
B-737-86N........................  CASINO EXPRESS.....            1      121,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........      895,000         34,178,453         2.62
                                                                    ============================================
B-737-3Y0........................  PACE AIRLINES......            1      137,000  .................  ...........
B-757-256........................  PACE AIRLINES......            1      137,000  .................  ...........
B-757-236........................  PACE AIRLINES......            1      137,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........      411,000         40,411,353         1.02
----------------------------------------------------------------------------------------------------------------

Describe the Alternatives Considered
    As described in the Analysis of Alternatives section, we evaluated
the following 8 alternatives to the final rule.

ALTERNATIVE 1. Cover only air carrier passenger airplanes
ALTERNATIVE 2. Exclude auxiliary fuel tanks
ALTERNATIVE 3. Cover only air carrier retrofitted passenger airplanes
ALTERNATIVE 4. Cover only air carrier production passenger airplanes
ALTERNATIVE 5. Cover only air carrier production passenger and cargo
airplanes
ALTERNATIVE 6. Final rule plus part 91 airplanes
ALTERNATIVE 7. Final rule plus conversion cargo airplanes
ALTERNATIVE 8. Final rule plus conversion and retrofitted cargo
airplanes

    Our conclusion was that the final rule provided the best balance of
cost and benefits for the United States society. Whether an airplane is
flown by a small entity or by a large entity, the risk is largely the
same. Consequently, we determined that the final rule should apply to
all passenger airplanes and to production cargo airplanes.
Regulatory Flexibility Analysis Summary
    As the rule will have a significant economic impact on three small
operators, we determined this final rule will have a significant impact
on a substantial number of small entities.
International Trade Analysis
    The Trade Agreements Act of 1979 (Pub. L. 96-39), as amended by the
Uruguay Round Agreements Act (Pub. L. 103-465), prohibits Federal
agencies from establishing any standards or engaging in related
activities that create unnecessary obstacles to the foreign commerce of
the United States. Pursuant to these Acts, the establishment of
standards are not considered unnecessary obstacles to the foreign
commerce of the United States, when the standards have a legitimate
domestic objective, such as the protection of safety, and when the
standards do not operate in a manner that excludes imports that meet
this objective. The statute also requires consideration of
international standards and, where appropriate, that they be the basis
for U.S. standards. The FAA notes the purpose of this rule is to ensure
the safety of the American public. We have assessed the effects of this
rule to ensure that it does not exclude imports that meet this
objective. As a result, this rule is not considered as creating
unnecessary obstacles to foreign commerce.
Unfunded Mandates Act
    Title II of the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-
4)

[[Page 42493]]

requires each Federal agency to prepare a written statement assessing
the effects of any Federal mandate in a proposed or final agency rule
that may result in an expenditure of $100 million or more (adjusted
annually for inflation with the base year 1995) in any one year by
State, local, and tribal governments, in the aggregate, or by the
private sector; such a mandate is deemed to be a ``significant
regulatory action.'' The FAA currently uses an inflation-adjusted value
of $136.1 million in lieu of $100 million.
    There will be 3 years (2015, 2016, and 2017) in which the
undiscounted costs will be greater than $136.1 million. Consequently,
in Table 7 of the regulatory evaluation summary, we evaluated the costs
and benefits of 8 alternatives to the final rule.

Executive Order 13132, Federalism

    The FAA has analyzed this rule under the principles and criteria of
Executive Order 13132, Federalism. We determined that this action will
not have a substantial direct effect on the States, on the relationship
between the national Government and the States, or on the distribution
of power and responsibilities among the various levels of government,
and therefore will not have federalism implications.

Regulations Affecting Intrastate Aviation in Alaska

    Section 1205 of the FAA Reauthorization Act of 1996 (110 Stat.
3213) requires the Administrator, when modifying regulations in title
14 of the CFR in manner affecting intrastate aviation in Alaska, to
consider the extent to which Alaska is not served by transportation
modes other than aviation, and to establish such regulatory
distinctions, as he or she considers appropriate. Because this rule
applies to the certification of future designs of transport category
airplanes and their subsequent operation, it could affect intrastate
aviation in Alaska. Nevertheless, the FAA has determined that it is
inappropriate to relieve intrastate aviation interests in Alaska from
the requirements of today's rule because of the safety objective served
by this rule.

Environmental Analysis

    FAA Order 1050.1E identifies FAA actions that are categorically
excluded from preparation of an environmental assessment or
environmental impact statement under the National Environmental Policy
Act in the absence of extraordinary circumstances. The FAA has
determined this rulemaking action qualifies for the categorical
exclusion identified in paragraph 312f and involves no extraordinary
circumstances.

Regulations that Significantly Affect Energy Supply, Distribution, or
Use

    The FAA has analyzed this rule under Executive Order 13211, Actions
Concerning Regulations that Significantly Affect Energy Supply,
Distribution, or Use (May 18, 2001). We have determined that it is not
a ``significant energy action'' under the executive order because the
rule is not likely to have a significant adverse effect on the supply,
distribution, or use of energy.

Submission of Comments

Request for Comments

    Comments should be submitted to Docket No. FAA-2005-22997 by
January 20, 2009. Comments may be submitted to the docket using any of
the means listed in the Addresses section below.
    We will file in the docket all comments we receive, as well as a
report summarizing each substantive public contact with FAA personnel
concerning this rulemaking. The docket is available for public
inspection before and after the comment closing date.
    Privacy Act: We will post all comments we receive, without change,
to http://www.regulations.gov, including any personal information you
provide. Using the search function of our docket Web site, anyone can
find and read the comments received into any of our dockets, including
the name of the individual sending the comment (or signing the comment
for an association, business, labor union, etc.). You may review DOT's
complete Privacy Act Statement in the Federal Register published on
April 11, 2000 (65 FR 19477-78) or you may visit http://
DocketsInfo.dot.gov.

Proprietary or Confidential Business Information

    Do not file in the docket information that you consider to be
proprietary or confidential business information. Send or deliver this
information directly to the person identified in the FOR FURTHER
INFORMATION CONTACT section of this document. You must mark the
information that you consider proprietary or confidential. If you send
the information on a disk or CD ROM, mark the outside of the disk or CD
ROM and also identify electronically within the disk or CD ROM the
specific information that is proprietary or confidential.
    Under 14 CFR 11.35(b), when we are aware of proprietary information
filed with a comment, we do not place it in the docket. We hold it in a
separate file to which the public does not have access, and we place a
note in the docket that we have received it. If we receive a request to
examine or copy this information, we treat it as any other request
under the Freedom of Information Act (5 U.S.C. 552). We process such a
request under the DOT procedures found in 49 CFR part 7.

ADDRESSES: You may send comments identified by Docket Number FAA-2004-
22997 using any of the following methods:
     Federal eRulemaking Portal: Go to http://
www.regulations.gov and follow the online instructions for sending your
comments electronically.
     Mail: Send comments to Docket Operations, M-30, U.S.
Department of Transportation, 1200 New Jersey Avenue, SE., West
Building Ground Floor, Room W12-140, Washington, DC 20590-0001.
     Fax: Fax comments to the Docket Operations at 202-493-
2251.
     Hand Delivery or Courier: Bring comments to Docket
Operations in Room W12-140 of the West Building Ground Floor at 1200
New Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal holidays.
    Docket: To read background documents or comments received, go to
http://www.regulations.gov at any time or to Room W12-140 of the West
Building Ground Floor at 1200 New Jersey Avenue, SE., Washington, DC,
between 9 a.m. and 5 p.m., Monday through Friday, except Federal
holidays.

Availability of Rulemaking Documents

    You can get an electronic copy using the Internet by:
    (1) Searching the Federal eRulemaking Portal (http://
www.regulations.gov);
    (2) Visiting the FAA's Regulations and Policies Web page at http://
www.faa.gov/regulations_policies/; or
    (3) Accessing the Government Printing Office's web page at http://
www.gpoaccess.gov/fr/index.html.
    You can also get a copy by submitting a request to the Federal
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence
Avenue, SW., Washington, DC 20591, or by calling (202) 267-9680. Make
sure to identify the docket number, or amendment number of this
rulemaking.

Small Business Regulatory Enforcement Fairness Act

    The Small Business Regulatory Enforcement Fairness Act (SFREFA) of
1996 requires FAA to comply with

[[Page 42494]]

small entity requests for information or advice about compliance with
statutes and regulations within its jurisdiction. If you are a small
entity and you have a question regarding this document, you may contact
its local FAA official, or the person listed under FOR FURTHER
INFORMATION CONTACT. You can find out more about SBREFA on the Internet
at http://www.faa.gov/regulations_policies/rulemaking/sbre_act/.

List of Subjects

14 CFR part 25

    Aircraft, Aviation safety, Incorporation by reference, Reporting
and recordkeeping requirements.

14 CFR part 26

    Aircraft, Aviation safety, Continued airworthiness.

14 CFR part 121

    Air carriers, Aircraft, Aviation safety, Reporting and
recordkeeping requirements, Safety, Transportation.

14 CFR part 125

    Aircraft, Aviation safety, Reporting and recordkeeping
requirements.

14 CFR part 129

    Air carriers, Aircraft, Aviation safety, Reporting and
recordkeeping requirements, Security measures.

V. The Amendment

0
In consideration of the foregoing, the Federal Aviation Administration
amends Chapter 1 of Title 14, Code of Federal Regulations (CFR) parts
25, 26, 121, 125, and 129, as follows:

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

0
1. The authority citation for part 25 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702 and 44704.


0
2. Part 25 is amended by adding a new Sec.  25.5 to read as follows:


Sec.  25.5  Incorporations by reference.

    (a) The materials listed in this section are incorporated by
reference in the corresponding sections noted. These incorporations by
reference were approved by the Director of the Federal Register in
accordance with 5 U.S.C. 552(a) and 1 CFR part 51. These materials are
incorporated as they exist on the date of the approval, and notice of
any change in these materials will be published in the Federal
Register. The materials are available for purchase at the corresponding
addresses noted below, and all are available for inspection at the
National Archives and Records Administration (NARA), and at FAA,
Transport Airplane Directorate, Aircraft Certification Service, 1601
Lind Avenue, SW., Renton, Washington 98057-3356. For information on the
availability of this material at NARA, call 202-741-6030, or go to:
http://www.archives.gov/federal_register/code_of_federal_
regulations/ibr_locations.html.
    (b) The following materials are available for purchase from the
following address: The National Technical Information Services (NTIS),
Springfield, Virginia 22166.
    (1) Fuel Tank Flammability Assessment Method User's Manual, dated
May 2008, document number DOT/FAA/AR-05/8, IBR approved for Sec.
25.981 and Appendix N. It can also be obtained at the following Web
site: http://www.fire.tc.faa.gov/systems/fueltank/FTFAM.stm.
    (2) [Reserved]

0
3. Amend Sec.  25.981 by revising paragraphs (b) and (c) and adding a
new paragraph (d) to read as follows:


Sec.  25.981  Fuel tank explosion prevention.

* * * * *
    (b) Except as provided in paragraphs (b)(2) and (c) of this
section, no fuel tank Fleet Average Flammability Exposure on an
airplane may exceed three percent of the Flammability Exposure
Evaluation Time (FEET) as defined in Appendix N of this part, or that
of a fuel tank within the wing of the airplane model being evaluated,
whichever is greater. If the wing is not a conventional unheated
aluminum wing, the analysis must be based on an assumed Equivalent
Conventional Unheated Aluminum Wing Tank.
    (1) Fleet Average Flammability Exposure is determined in accordance
with Appendix N of this part. The assessment must be done in accordance
with the methods and procedures set forth in the Fuel Tank Flammability
Assessment Method User's Manual, dated May 2008, document number DOT/
FAA/AR-05/8 (incorporated by reference, see Sec.  25.5).
    (2) Any fuel tank other than a main fuel tank on an airplane must
meet the flammability exposure criteria of Appendix M to this part if
any portion of the tank is located within the fuselage contour.
    (3) As used in this paragraph,
    (i) Equivalent Conventional Unheated Aluminum Wing Tank is an
integral tank in an unheated semi-monocoque aluminum wing of a subsonic
airplane that is equivalent in aerodynamic performance, structural
capability, fuel tank capacity and tank configuration to the designed
wing.
    (ii) Fleet Average Flammability Exposure is defined in Appendix N
to this part and means the percentage of time each fuel tank ullage is
flammable for a fleet of an airplane type operating over the range of
flight lengths.
    (iii) Main Fuel Tank means a fuel tank that feeds fuel directly
into one or more engines and holds required fuel reserves continually
throughout each flight.
    (c) Paragraph (b) of this section does not apply to a fuel tank if
means are provided to mitigate the effects of an ignition of fuel
vapors within that fuel tank such that no damage caused by an ignition
will prevent continued safe flight and landing.
    (d) Critical design configuration control limitations (CDCCL),
inspections, or other procedures must be established, as necessary, to
prevent development of ignition sources within the fuel tank system
pursuant to paragraph (a) of this section, to prevent increasing the
flammability exposure of the tanks above that permitted under paragraph
(b) of this section, and to prevent degradation of the performance and
reliability of any means provided according to paragraphs (a) or (c) of
this section. These CDCCL, inspections, and procedures must be included
in the Airworthiness Limitations section of the instructions for
continued airworthiness required by Sec.  25.1529. Visible means of
identifying critical features of the design must be placed in areas of
the airplane where foreseeable maintenance actions, repairs, or
alterations may compromise the critical design configuration control
limitations (e.g., color-coding of wire to identify separation
limitation). These visible means must also be identified as CDCCL.

0
4. Part 25 is amended by adding a new APPENDIX M to read as follows:

APPENDIX M TO PART 25--FUEL TANK SYSTEM FLAMMABILITY REDUCTION MEANS

    M25.1 Fuel tank flammability exposure requirements.
    (a) The Fleet Average Flammability Exposure of each fuel tank,
as determined in accordance with Appendix N of this part, may not
exceed 3 percent of the Flammability Exposure Evaluation Time
(FEET), as defined in Appendix N of this part. As a portion of this
3 percent, if flammability reduction means (FRM) are used, each of
the following time periods may not exceed 1.8 percent of the FEET:
    (1) When any FRM is operational but the fuel tank is not inert
and the tank is flammable; and
    (2) When any FRM is inoperative and the tank is flammable.
    (b) The Fleet Average Flammability Exposure, as defined in
Appendix N of this

[[Page 42495]]

part, of each fuel tank may not exceed 3 percent of the portion of
the FEET occurring during either ground or takeoff/climb phases of
flight during warm days. The analysis must consider the following
conditions.
    (1) The analysis must use the subset of those flights that begin
with a sea level ground ambient temperature of 80[deg] F (standard
day plus 21[deg] F atmosphere) or above, from the flammability
exposure analysis done for overall performance.
    (2) For the ground and takeoff/climb phases of flight, the
average flammability exposure must be calculated by dividing the
time during the specific flight phase the fuel tank is flammable by
the total time of the specific flight phase.
    (3) Compliance with this paragraph may be shown using only those
flights for which the airplane is dispatched with the flammability
reduction means operational.
    M25.2 Showing compliance.
    (a) The applicant must provide data from analysis, ground
testing, and flight testing, or any combination of these, that:
    (1) Validate the parameters used in the analysis required by
paragraph M25.1 of this appendix;
    (2) Substantiate that the FRM is effective at limiting
flammability exposure in all compartments of each tank for which the
FRM is used to show compliance with paragraph M25.1 of this
appendix; and
    (3) Describe the circumstances under which the FRM would not be
operated during each phase of flight.
    (b) The applicant must validate that the FRM meets the
requirements of paragraph M25.1 of this appendix with any airplane
or engine configuration affecting the performance of the FRM for
which approval is sought.
    M25.3 Reliability indications and maintenance access.
    (a) Reliability indications must be provided to identify
failures of the FRM that would otherwise be latent and whose
identification is necessary to ensure the fuel tank with an FRM
meets the fleet average flammability exposure requirements listed in
paragraph M25.1 of this appendix, including when the FRM is
inoperative.
    (b) Sufficient accessibility to FRM reliability indications must
be provided for maintenance personnel or the flightcrew.
    (c) The access doors and panels to the fuel tanks with FRMs
(including any tanks that communicate with a tank via a vent
system), and to any other confined spaces or enclosed areas that
could contain hazardous atmosphere under normal conditions or
failure conditions, must be permanently stenciled, marked, or
placarded to warn maintenance personnel of the possible presence of
a potentially hazardous atmosphere.
    M25.4 Airworthiness limitations and procedures.
    (a) If FRM is used to comply with paragraph M25.1 of this
appendix, Airworthiness Limitations must be identified for all
maintenance or inspection tasks required to identify failures of
components within the FRM that are needed to meet paragraph M25.1 of
this appendix.
    (b) Maintenance procedures must be developed to identify any
hazards to be considered during maintenance of the FRM. These
procedures must be included in the instructions for continued
airworthiness (ICA).
    M25.5 Reliability reporting.
    The effects of airplane component failures on FRM reliability
must be assessed on an on-going basis. The applicant/holder must do
the following:
    (a) Demonstrate effective means to ensure collection of FRM
reliability data. The means must provide data affecting FRM
reliability, such as component failures.
    (b) Unless alternative reporting procedures are approved by the
FAA Oversight Office, as defined in part 26 of this subchapter,
provide a report to the FAA every six months for the first five
years after service introduction. After that period, continued
reporting every six months may be replaced with other reliability
tracking methods found acceptable to the FAA or eliminated if it is
established that the reliability of the FRM meets, and will continue
to meet, the exposure requirements of paragraph M25.1 of this
appendix.
    (c) Develop service instructions or revise the applicable
airplane manual, according to a schedule approved by the FAA
Oversight Office, as defined in part 26 of this subchapter, to
correct any failures of the FRM that occur in service that could
increase any fuel tank's Fleet Average Flammability Exposure to more
than that required by paragraph M25.1 of this appendix.


0
5. Part 25 is amended by adding a new APPENDIX N to read as follows:

APPENDIX N TO PART 25--FUEL TANK FLAMMABILITY EXPOSURE AND RELIABILITY
ANALYSIS

    N25.1 General.
    (a) This appendix specifies the requirements for conducting fuel
tank fleet average flammability exposure analyses required to meet
Sec.  25.981(b) and Appendix M of this part. For fuel tanks
installed in aluminum wings, a qualitative assessment is sufficient
if it substantiates that the tank is a conventional unheated wing
tank.
    (b) This appendix defines parameters affecting fuel tank
flammability that must be used in performing the analysis. These
include parameters that affect all airplanes within the fleet, such
as a statistical distribution of ambient temperature, fuel flash
point, flight lengths, and airplane descent rate. Demonstration of
compliance also requires application of factors specific to the
airplane model being evaluated. Factors that need to be included are
maximum range, cruise mach number, typical altitude where the
airplane begins initial cruise phase of flight, fuel temperature
during both ground and flight times, and the performance of a
flammability reduction means (FRM) if installed.
    (c) The following definitions, input variables, and data tables
must be used in the program to determine fleet average flammability
exposure for a specific airplane model.
    N25.2 Definitions.
    (a) Bulk Average Fuel Temperature means the average fuel
temperature within the fuel tank or different sections of the tank
if the tank is subdivided by baffles or compartments.
    (b) Flammability Exposure Evaluation Time (FEET). The time from
the start of preparing the airplane for flight, through the flight
and landing, until all payload is unloaded, and all passengers and
crew have disembarked. In the Monte Carlo program, the flight time
is randomly selected from the Flight Length Distribution (Table 2),
the pre-flight times are provided as a function of the flight time,
and the post-flight time is a constant 30 minutes.
    (c) Flammable. With respect to a fluid or gas, flammable means
susceptible to igniting readily or to exploding (14 CFR Part 1,
Definitions). A non-flammable ullage is one where the fuel-air vapor
is too lean or too rich to burn or is inert as defined below. For
the purposes of this appendix, a fuel tank that is not inert is
considered flammable when the bulk average fuel temperature within
the tank is within the flammable range for the fuel type being used.
For any fuel tank that is subdivided into sections by baffles or
compartments, the tank is considered flammable when the bulk average
fuel temperature within any section of the tank, that is not inert,
is within the flammable range for the fuel type being used.
    (d) Flash Point. The flash point of a flammable fluid means the
lowest temperature at which the application of a flame to a heated
sample causes the vapor to ignite momentarily, or ``flash.'' Table 1
of this appendix provides the flash point for the standard fuel to
be used in the analysis.
    (e) Fleet average flammability exposure is the percentage of the
flammability exposure evaluation time (FEET) each fuel tank ullage
is flammable for a fleet of an airplane type operating over the
range of flight lengths in a world-wide range of environmental
conditions and fuel properties as defined in this appendix.
    (f) Gaussian Distribution is another name for the normal
distribution, a symmetrical frequency distribution having a precise
mathematical formula relating the mean and standard deviation of the
samples. Gaussian distributions yield bell-shaped frequency curves
having a preponderance of values around the mean with progressively
fewer observations as the curve extends outward.
    (g) Hazardous atmosphere. An atmosphere that may expose
maintenance personnel, passengers or flight crew to the risk of
death, incapacitation, impairment of ability to self-rescue (that
is, escape unaided from a confined space), injury, or acute illness.
    (h) Inert. For the purpose of this appendix, the tank is
considered inert when the bulk average oxygen concentration within
each compartment of the tank is 12 percent or less from sea level up
to 10,000 feet altitude, then linearly increasing from 12 percent at
10,000 feet to 14.5 percent at 40,000 feet altitude, and
extrapolated linearly above that altitude.
    (i) Inerting. A process where a noncombustible gas is introduced
into the ullage of a fuel tank so that the ullage becomes non-
flammable.
    (j) Monte Carlo Analysis. The analytical method that is
specified in this appendix as the compliance means for assessing the
fleet average flammability exposure time for a fuel tank.

[[Page 42496]]

    (k) Oxygen evolution occurs when oxygen dissolved in the fuel is
released into the ullage as the pressure and temperature in the fuel
tank are reduced.
    (l) Standard deviation is a statistical measure of the
dispersion or variation in a distribution, equal to the square root
of the arithmetic mean of the squares of the deviations from the
arithmetic means.
    (m) Transport Effects. For purposes of this appendix, transport
effects are the change in fuel vapor concentration in a fuel tank
caused by low fuel conditions and fuel condensation and
vaporization.
    (n) Ullage. The volume within the fuel tank not occupied by
liquid fuel.
    N25.3 Fuel tank flammability exposure analysis.
    (a) A flammability exposure analysis must be conducted for the
fuel tank under evaluation to determine fleet average flammability
exposure for the airplane and fuel types under evaluation. For fuel
tanks that are subdivided by baffles or compartments, an analysis
must be performed either for each section of the tank, or for the
section of the tank having the highest flammability exposure.
Consideration of transport effects is not allowed in the analysis.
The analysis must be done in accordance with the methods and
procedures set forth in the Fuel Tank Flammability Assessment Method
User's Manual, dated May 2008, document number DOT/FAA/AR-05/8
(incorporated by reference, see Sec.  25.5). The parameters
specified in sections N25.3(b) and (c) of this appendix must be used
in the fuel tank flammability exposure ``Monte Carlo'' analysis.
    (b) The following parameters are defined in the Monte Carlo
analysis and provided in paragraph N25.4 of this appendix:
    (1) Cruise Ambient Temperature, as defined in this appendix.
    (2) Ground Ambient Temperature, as defined in this appendix.
    (3) Fuel Flash Point, as defined in this appendix.
    (4) Flight Length Distribution, as defined in Table 2 of this
appendix.
    (5) Airplane Climb and Descent Profiles, as defined in the Fuel
Tank Flammability Assessment Method User's Manual, dated May 2008,
document number DOT/FAA/AR-05/8 (incorporated by reference in Sec.
25.5).
    (c) Parameters that are specific to the particular airplane
model under evaluation that must be provided as inputs to the Monte
Carlo analysis are:
    (1) Airplane cruise altitude.
    (2) Fuel tank quantities. If fuel quantity affects fuel tank
flammability, inputs to the Monte Carlo analysis must be provided
that represent the actual fuel quantity within the fuel tank or
compartment of the fuel tank throughout each of the flights being
evaluated. Input values for this data must be obtained from ground
and flight test data or the approved FAA fuel management procedures.
    (3) Airplane cruise mach number.
    (4) Airplane maximum range.
    (5) Fuel tank thermal characteristics. If fuel temperature
affects fuel tank flammability, inputs to the Monte Carlo analysis
must be provided that represent the actual bulk average fuel
temperature within the fuel tank at each point in time throughout
each of the flights being evaluated. For fuel tanks that are
subdivided by baffles or compartments, bulk average fuel temperature
inputs must be provided for each section of the tank. Input values
for these data must be obtained from ground and flight test data or
a thermal model of the tank that has been validated by ground and
flight test data.
    (6) Maximum airplane operating temperature limit, as defined by
any limitations in the airplane flight manual.
    (7) Airplane Utilization. The applicant must provide data
supporting the number of flights per day and the number of hours per
flight for the specific airplane model under evaluation. If there is
no existing airplane fleet data to support the airplane being
evaluated, the applicant must provide substantiation that the number
of flights per day and the number of hours per flight for that
airplane model is consistent with the existing fleet data they
propose to use.
    (d) Fuel Tank FRM Model. If FRM is used, an FAA approved Monte
Carlo program must be used to show compliance with the flammability
requirements of Sec.  25.981 and Appendix M of this part. The
program must determine the time periods during each flight phase
when the fuel tank or compartment with the FRM would be flammable.
The following factors must be considered in establishing these time
periods:
    (1) Any time periods throughout the flammability exposure
evaluation time and under the full range of expected operating
conditions, when the FRM is operating properly but fails to maintain
a non-flammable fuel tank because of the effects of the fuel tank
vent system or other causes,
    (2) If dispatch with the system inoperative under the Master
Minimum Equipment List (MMEL) is requested, the time period assumed
in the reliability analysis (60 flight hours must be used for a 10-
day MMEL dispatch limit unless an alternative period has been
approved by the Administrator),
    (3) Frequency and duration of time periods of FRM inoperability,
substantiated by test or analysis acceptable to the FAA, caused by
latent or known failures, including airplane system shut-downs and
failures that could cause the FRM to shut down or become
inoperative.
    (4) Effects of failures of the FRM that could increase the
flammability exposure of the fuel tank.
    (5) If an FRM is used that is affected by oxygen concentrations
in the fuel tank, the time periods when oxygen evolution from the
fuel results in the fuel tank or compartment exceeding the inert
level. The applicant must include any times when oxygen evolution
from the fuel in the tank or compartment under evaluation would
result in a flammable fuel tank. The oxygen evolution rate that must
be used is defined in the Fuel Tank Flammability Assessment Method
User's Manual, dated May 2008, document number DOT/FAA/AR-05/8
(incorporated by reference in Sec.  25.5).
    (6) If an inerting system FRM is used, the effects of any air
that may enter the fuel tank following the last flight of the day
due to changes in ambient temperature, as defined in Table 4, during
a 12-hour overnight period.
    (e) The applicant must submit to the FAA Oversight Office for
approval the fuel tank flammability analysis, including the
airplane-specific parameters identified under paragraph N25.3(c) of
this appendix and any deviations from the parameters identified in
paragraph N25.3(b) of this appendix that affect flammability
exposure, substantiating data, and any airworthiness limitations and
other conditions assumed in the analysis.
    N25.4 Variables and data tables.
    The following data must be used when conducting a flammability
exposure analysis to determine the fleet average flammability
exposure. Variables used to calculate fleet flammability exposure
must include atmospheric ambient temperatures, flight length,
flammability exposure evaluation time, fuel flash point, thermal
characteristics of the fuel tank, overnight temperature drop, and
oxygen evolution from the fuel into the ullage.
    (a) Atmospheric Ambient Temperatures and Fuel Properties.
    (1) In order to predict flammability exposure during a given
flight, the variation of ground ambient temperatures, cruise ambient
temperatures, and a method to compute the transition from ground to
cruise and back again must be used. The variation of the ground and
cruise ambient temperatures and the flash point of the fuel is
defined by a Gaussian curve, given by the 50 percent value and a
1-standard deviation value.
    (2) Ambient Temperature: Under the program, the ground and
cruise ambient temperatures are linked by a set of assumptions on
the atmosphere. The temperature varies with altitude following the
International Standard Atmosphere (ISA) rate of change from the
ground ambient temperature until the cruise temperature for the
flight is reached. Above this altitude, the ambient temperature is
fixed at the cruise ambient temperature. This results in a variation
in the upper atmospheric temperature. For cold days, an inversion is
applied up to 10,000 feet, and then the ISA rate of change is used.
    (3) Fuel properties:
    (i) For Jet A fuel, the variation of flash point of the fuel is
defined by a Gaussian curve, given by the 50 percent value and a
1-standard deviation, as shown in Table 1 of this
appendix.
    (ii) The flammability envelope of the fuel that must be used for
the flammability exposure analysis is a function of the flash point
of the fuel selected by the Monte Carlo for a given flight. The
flammability envelope for the fuel is defined by the upper
flammability limit (UFL) and lower flammability limit (LFL) as
follows:
    (A) LFL at sea level = flash point temperature of the fuel at
sea level minus 10 [deg] F. LFL decreases from sea level value with
increasing altitude at a rate of 1 [deg]F per 808 feet.
    (B) UFL at sea level = flash point temperature of the fuel at
sea level plus 63.5 [deg] F. UFL decreases from the sea level value
with increasing altitude at a rate of 1 [deg]F per 512 feet.

[[Page 42497]]

    (4) For each flight analyzed, a separate random number must be
generated for each of the three parameters (ground ambient
temperature, cruise ambient temperature, and fuel flash point) using
the Gaussian distribution defined in Table 1 of this appendix.

Table 1.--Gaussian Distribution for Ground Ambient Temperature, Cruise Ambient Temperature, and Fuel Flash Point
----------------------------------------------------------------------------------------------------------------
                                                                            Temperature in deg F
                                                           -----------------------------------------------------
                         Parameter                           Ground ambient    Cruise ambient   Fuel flash point
                                                               temperature       temperature          (FP)
----------------------------------------------------------------------------------------------------------------
Mean Temp.................................................             59.95               -70               120
Neg 1 std dev.............................................             20.14                 8                 8
Pos 1 std dev.............................................             17.28                 8                 8
----------------------------------------------------------------------------------------------------------------

    (b) The Flight Length Distribution defined in Table 2 must be
used in the Monte Carlo analysis.

                                      Table 2.--Flight Length Distribution
----------------------------------------------------------------------------------------------------------------
Flight length (NM)                           Airplane maximum range--nautical miles (NM)
----------------------------------------------------------------------------------------------------------------
  From       To       1000      2000      3000      4000      5000     6000     7000     8000     9000    10000
----------------------------------------------------------------------------------------------------------------
          ........                      Distribution of flight lengths (percentage of total)
----------------------------------------------------------------------------------------------------------------
      0       200      11.7       7.5       6.2       5.5       4.7      4.0      3.4      3.0      2.6      2.3
    200       400      27.3      19.9      17.0      15.2      13.2     11.4      9.7      8.5      7.5      6.7
    400       600      46.3      40.0      35.7      32.6      28.5     24.9     21.2     18.7     16.4     14.8
    600       800      10.3      11.6      11.0      10.2       9.1      8.0      6.9      6.1      5.4      4.8
    800      1000       4.4       8.5       8.6       8.2       7.4      6.6      5.7      5.0      4.5      4.0
   1000      1200       0.0       4.8       5.3       5.3       4.8      4.3      3.8      3.3      3.0      2.7
   1200      1400       0.0       3.6       4.4       4.5       4.2      3.8      3.3      3.0      2.7      2.4
   1400      1600       0.0       2.2       3.3       3.5       3.3      3.1      2.7      2.4      2.2      2.0
   1600      1800       0.0       1.2       2.3       2.6       2.5      2.4      2.1      1.9      1.7      1.6
   1800      2000       0.0       0.7       2.2       2.6       2.6      2.5      2.2      2.0      1.8      1.7
   2000      2200       0.0       0.0       1.6       2.1       2.2      2.1      1.9      1.7      1.6      1.4
   2200      2400       0.0       0.0       1.1       1.6       1.7      1.7      1.6      1.4      1.3      1.2
   2400      2600       0.0       0.0       0.7       1.2       1.4      1.4      1.3      1.2      1.1      1.0
   2600      2800       0.0       0.0       0.4       0.9       1.0      1.1      1.0      0.9      0.9      0.8
   2800      3000       0.0       0.0       0.2       0.6       0.7      0.8      0.7      0.7      0.6      0.6
   3000      3200       0.0       0.0       0.0       0.6       0.8      0.8      0.8      0.8      0.7      0.7
   3200      3400       0.0       0.0       0.0       0.7       1.1      1.2      1.2      1.1      1.1      1.0
   3400      3600       0.0       0.0       0.0       0.7       1.3      1.6      1.6      1.5      1.5      1.4
   3600      3800       0.0       0.0       0.0       0.9       2.2      2.7      2.8      2.7      2.6      2.5
   3800      4000       0.0       0.0       0.0       0.5       2.0      2.6      2.8      2.8      2.7      2.6
   4000      4200       0.0       0.0       0.0       0.0       2.1      3.0      3.2      3.3      3.2      3.1
   4200      4400       0.0       0.0       0.0       0.0       1.4      2.2      2.5      2.6      2.6      2.5
   4400      4600       0.0       0.0       0.0       0.0       1.0      2.0      2.3      2.5      2.5      2.4
   4600      4800       0.0       0.0       0.0       0.0       0.6      1.5      1.8      2.0      2.0      2.0
   4800      5000       0.0       0.0       0.0       0.0       0.2      1.0      1.4      1.5      1.6      1.5
   5000      5200       0.0       0.0       0.0       0.0       0.0      0.8      1.1      1.3      1.3      1.3
   5200      5400       0.0       0.0       0.0       0.0       0.0      0.8      1.2      1.5      1.6      1.6
   5400      5600       0.0       0.0       0.0       0.0       0.0      0.9      1.7      2.1      2.2      2.3
   5600      5800       0.0       0.0       0.0       0.0       0.0      0.6      1.6      2.2      2.4      2.5
   5800      6000       0.0       0.0       0.0       0.0       0.0      0.2      1.8      2.4      2.8      2.9
   6000      6200       0.0       0.0       0.0       0.0       0.0      0.0      1.7      2.6      3.1      3.3
   6200      6400       0.0       0.0       0.0       0.0       0.0      0.0      1.4      2.4      2.9      3.1
   6400      6600       0.0       0.0       0.0       0.0       0.0      0.0      0.9      1.8      2.2      2.5
   6600      6800       0.0       0.0       0.0       0.0       0.0      0.0      0.5      1.2      1.6      1.9
   6800      7000       0.0       0.0       0.0       0.0       0.0      0.0      0.2      0.8      1.1      1.3
   7000      7200       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.4      0.7      0.8
   7200      7400       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.3      0.5      0.7
   7400      7600       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.2      0.5      0.6
   7600      7800       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.1      0.5      0.7
   7800      8000       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.1      0.6      0.8
   8000      8200       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.5      0.8
   8200      8400       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.5      1.0
   8400      8600       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.6      1.3
   8600      8800       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.4      1.1
   8800      9000       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.2      0.8
   9000      9200       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.0      0.5
   9200      9400       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.0      0.2

[[Page 42498]]


   9400      9600       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.0      0.1
   9600      9800       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.0      0.1
   9800     10000       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.0      0.1
----------------------------------------------------------------------------------------------------------------

    (c) Overnight Temperature Drop. For airplanes on which FRM is
installed, the overnight temperature drop for this appendix is
defined using:
    (1) A temperature at the beginning of the overnight period that
equals the landing temperature of the previous flight that is a
random value based on a Gaussian distribution; and
    (2) An overnight temperature drop that is a random value based
on a Gaussian distribution.
    (3) For any flight that will end with an overnight ground period
(one flight per day out of an average number of flights per day,
depending on utilization of the particular airplane model being
evaluated), the landing outside air temperature (OAT) is to be
chosen as a random value from the following Gaussian curve:

                Table 3.--Landing Outside Air Temperature
------------------------------------------------------------------------
                                                        Landing outside
                      Parameter                         air temperature
                                                             [deg]F
------------------------------------------------------------------------
Mean Temperature.....................................              58.68
negative 1 std dev...................................              20.55
positive 1 std dev...................................              13.21
------------------------------------------------------------------------

    (4) The outside ambient air temperature (OAT) overnight
temperature drop is to be chosen as a random value from the
following Gaussian curve:

              Table 4.--Outside Air Temperature (OAT) Drop
------------------------------------------------------------------------
                                                             OAT drop
                        Parameter                           temperature
                                                              [deg]F
------------------------------------------------------------------------
Mean Temp...............................................            12.0
1 std dev...............................................             6.0
------------------------------------------------------------------------

    (d) Number of Simulated Flights Required in Analysis. In order
for the Monte Carlo analysis to be valid for showing compliance with
the fleet average and warm day flammability exposure requirements,
the applicant must run the analysis for a minimum number of flights
to ensure that the fleet average and warm day flammability exposure
for the fuel tank under evaluation meets the applicable flammability
limits defined in Table 5 of this appendix.

                  Table 5.--Flammability Exposure Limit
------------------------------------------------------------------------
                                         Maximum            Maximum
                                     acceptable Monte   acceptable Monte
                                      Carlo average      Carlo average
                                        fuel tank          fuel tank
Minimum number of flights in Monte     flammability       flammability
          Carlo analysis                 exposure           exposure
                                    (percent) to meet  (percent) to meet
                                        3 percent      7 percent part 26
                                       requirements       requirements
------------------------------------------------------------------------
10,000............................               2.91               6.79
100,000...........................               2.98               6.96
1,000,000.........................               3.00               7.00
------------------------------------------------------------------------

PART 26--CONTINUED AIRWORTHINESS AND SAFETY IMPROVEMENTS FOR
TRANSPORT CATEGORY AIRPLANES

0
6. The authority citation for part 26 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702 and 44704.


0
7. Revise Sec.  26.5 to read as follows:


Sec.  26.5  Applicability Table.

    Table 1 of this section provides an overview of the applicability
of this part. It provides guidance in identifying what sections apply
to various types of entities. The specific applicability of each
subpart and section is specified in the regulatory text.

                                    Table 1.--Applicability of Part 26 Rules
----------------------------------------------------------------------------------------------------------------
                                                                  Applicable sections
                                      --------------------------------------------------------------------------
                                        Subpart B EAPAS/    Subpart D fuel tank    Subpart E  damage tolerance
        Effective date of rule                 FTS             flammability                    data
                                      --------------------------------------------------------------------------
                                        December 10, 2007   September 19, 2008           January 11, 2008
----------------------------------------------------------------------------------------------------------------
Existing \1\ TC Holders..............               26.11                 26.33  26.43, 26.45, 26.49
Pending \1\ TC Applicants............               26.11                 26.37  26.43, 26.45
Existing \1\ STC Holders.............                 N/A                 26.35  26.47, 26.49
Pending \1\ STC/ATC Applicants.......               26.11                 26.35  26.45, 26.47, 26.49
Future \2\ STC/ATC Applicants........               26.11                 26.35  26.45, 26.47, 26.49
Manufacturers........................                 N/A                 26.39  N/A
----------------------------------------------------------------------------------------------------------------
\1\ As of the effective date of the identified rule.
\2\ Application made after the effective date of the identified rule.


[[Page 42499]]


0
8. Amend part 26 by adding a new subpart D to read as follows:
Subpart D--FUEL TANK FLAMMABILITY

General

Sec.
26.31 Definitions.
26.33 Holders of type certificates: Fuel tank flammability.
26.35 Changes to type certificates affecting fuel tank flammability.
26.37 Pending type certification projects: Fuel tank flammability.
26.39 Newly produced airplanes: Fuel tank flammability.

Subpart D--Fuel Tank Flammability

General


Sec.  26.31  Definitions.

    For purposes of this subpart--
    (a) Fleet Average Flammability Exposure has the meaning defined in
Appendix N of part 25 of this chapter.
    (b) Normally Emptied means a fuel tank other than a Main Fuel Tank.
Main Fuel Tank is defined in 14 CFR 25.981(b).


Sec.  26.33  Holders of type certificates: Fuel tank flammability.

    (a) Applicability. This section applies to U.S. type certificated
transport category, turbine-powered airplanes, other than those
designed solely for all-cargo operations, for which the State of
Manufacture issued the original certificate of airworthiness or export
airworthiness approval on or after January 1, 1992, that, as a result
of original type certification or later increase in capacity have:
    (1) A maximum type-certificated passenger capacity of 30 or more,
or
    (2) A maximum payload capacity of 7,500 pounds or more.
    (b) Flammability Exposure Analysis. (1) General. Within 150 days
after September 19, 2008, holders of type certificates must submit for
approval to the FAA Oversight Office a flammability exposure analysis
of all fuel tanks defined in the type design, as well as all design
variations approved under the type certificate that affect flammability
exposure. This analysis must be conducted in accordance with Appendix N
of part 25 of this chapter.
    (2) Exception. This paragraph (b) does not apply to--
    (i) Fuel tanks for which the type certificate holder has notified
the FAA under paragraph (g) of this section that it will provide design
changes and service instructions for Flammability Reduction Means or an
Ignition Mitigation Means (IMM) meeting the requirements of paragraph
(c) of this section.
    (ii) Fuel tanks substantiated to be conventional unheated aluminum
wing tanks.
    (c) Design Changes. For fuel tanks with a Fleet Average
Flammability Exposure exceeding 7 percent, one of the following design
changes must be made.
    (1) Flammability Reduction Means (FRM). A means must be provided to
reduce the fuel tank flammability.
    (i) Fuel tanks that are designed to be Normally Emptied must meet
the flammability exposure criteria of Appendix M of part 25 of this
chapter if any portion of the tank is located within the fuselage
contour.
    (ii) For all other fuel tanks, the FRM must meet all of the
requirements of Appendix M of part 25 of this chapter, except, instead
of complying with paragraph M25.1 of this appendix, the Fleet Average
Flammability Exposure may not exceed 7 percent.
    (2) Ignition Mitigation Means (IMM). A means must be provided to
mitigate the effects of an ignition of fuel vapors within the fuel tank
such that no damage caused by an ignition will prevent continued safe
flight and landing.
    (d) Service Instructions. No later than September 20, 2010, holders
of type certificates required by paragraph (c) of this section to make
design changes must meet the requirements specified in either paragraph
(d)(1) or (d)(2) of this section. The required service instructions
must identify each airplane subject to the applicability provisions of
paragraph (a) of this section.
    (1) FRM. The type certificate holder must submit for approval by
the FAA Oversight Office design changes and service instructions for
installation of fuel tank flammability reduction means (FRM) meeting
the criteria of paragraph (c) of this section.
    (2) IMM. The type certificate holder must submit for approval by
the FAA Oversight Office design changes and service instructions for
installation of fuel tank IMM that comply with 14 CFR 25.981(c) in
effect on September 19, 2008.
    (e) Instructions for Continued Airworthiness (ICA). No later than
September 20, 2010, holders of type certificates required by paragraph
(c) of this section to make design changes must submit for approval by
the FAA Oversight Office, critical design configuration control
limitations (CDCCL), inspections, or other procedures to prevent
increasing the flammability exposure of any tanks equipped with FRM
above that permitted under paragraph (c)(1) of this section and to
prevent degradation of the performance of any IMM provided under
paragraph (c)(2) of this section. These CDCCL, inspections, and
procedures must be included in the Airworthiness Limitations Section
(ALS) of the ICA required by 14 CFR 25.1529 or paragraph (f) of this
section. Unless shown to be impracticable, visible means to identify
critical features of the design must be placed in areas of the airplane
where foreseeable maintenance actions, repairs, or alterations may
compromise the critical design configuration limitations. These visible
means must also be identified as a CDCCL.
    (f) Airworthiness Limitations. Unless previously accomplished, no
later than September 20, 2010, holders of type certificates affected by
this section must establish an ALS of the maintenance manual or ICA for
each airplane configuration evaluated under paragraph (b)(1) of this
section and submit it to the FAA Oversight Office for approval. The ALS
must include a section that contains the CDCCL, inspections, or other
procedures developed under paragraph (e) of this section.
    (g) Compliance Plan for Flammability Exposure Analysis. Within 90
days after September 19, 2008, each holder of a type certificate
required to comply with paragraph (b) of this section must submit to
the FAA Oversight Office a compliance plan consisting of the following:
    (1) A proposed project schedule for submitting the required
analysis, or a determination that compliance with paragraph (b) of this
section is not required because design changes and service instructions
for FRM or IMM will be developed and made available as required by this
section.
    (2) A proposed means of compliance with paragraph (b) of this
section, if applicable.
    (h) Compliance Plan for Design Changes and Service Instructions.
Within 210 days after September 19, 2008, each holder of a type
certificate required to comply with paragraph (d) of this section must
submit to the FAA Oversight Office a compliance plan consisting of the
following:
    (1) A proposed project schedule, identifying all major milestones,
for meeting the compliance dates specified in paragraphs (d), (e) and
(f) of this section.
    (2) A proposed means of compliance with paragraphs (d), (e) and (f)
of this section.
    (3) A proposal for submitting a draft of all compliance items
required by paragraphs (d), (e) and (f) of this section for review by
the FAA Oversight Office

[[Page 42500]]

not less than 60 days before the compliance times specified in those
paragraphs.
    (4) A proposal for how the approved service information and any
necessary modification parts will be made available to affected
persons.
    (i) Each affected type certificate holder must implement the
compliance plans, or later revisions, as approved under paragraph (g)
and (h) of this section.


Sec.  26.35  Changes to type certificates affecting fuel tank
flammability.

    (a) Applicability. This section applies to holders and applicants
for approvals of the following design changes to any airplane subject
to 14 CFR 26.33(a):
    (1) Any fuel tank designed to be Normally Emptied if the fuel tank
installation was approved pursuant to a supplemental type certificate
or a field approval before September 19, 2008;
    (2) Any fuel tank designed to be Normally Emptied if an application
for a supplemental type certificate or an amendment to a type
certificate was made before September 19, 2008 and if the approval was
not issued before September 19, 2008; and
    (3) If an application for a supplemental type certificate or an
amendment to a type certificate is made on or September 19, 2008, any
of the following design changes:
    (i) Installation of a fuel tank designed to be Normally Emptied,
    (ii) Changes to existing fuel tank capacity, or
    (iii) Changes that may increase the flammability exposure of an
existing fuel tank for which FRM or IMM is required by Sec.  26.33(c).
    (b) Flammability Exposure Analysis-- (1) General. By the times
specified in paragraphs (b)(1)(i) and (b)(1)(ii) of this section, each
person subject to this section must submit for approval a flammability
exposure analysis of the auxiliary fuel tanks or other affected fuel
tanks, as defined in the type design, to the FAA Oversight Office. This
analysis must be conducted in accordance with Appendix N of part 25 of
this chapter.
    (i) Holders of supplemental type certificates and field approvals:
Within 12 months of September 19, 2008,
    (ii) Applicants for supplemental type certificates and for
amendments to type certificates: Within 12 months after September 19,
2008, or before the certificate is issued, whichever occurs later.
    (2) Exception. This paragraph does not apply to--
    (i) Fuel tanks for which the type certificate holder, supplemental
type certificate holder, or field approval holder has notified the FAA
under paragraph (f) of this section that it will provide design changes
and service instructions for an IMM meeting the requirements of Sec.
25.981(c) in effect September 19, 2008; and
    (ii) Fuel tanks substantiated to be conventional unheated aluminum
wing tanks.
    (c) Impact Assessment. By the times specified in paragraphs (c)(1)
and (c)(2) of this section, each person subject to paragraph (a)(1) of
this section holding an approval for installation of a Normally Emptied
fuel tank on an airplane model listed in Table 1 of this section, and
each person subject to paragraph (a)(3)(iii) of this section, must
submit for approval to the FAA Oversight Office an assessment of the
fuel tank system, as modified by their design change. The assessment
must identify any features of the design change that compromise any
critical design configuration control limitation (CDCCL) applicable to
any airplane on which the design change is eligible for installation.
    (1) Holders of supplemental type certificates and field approvals:
Before March 21, 2011.
    (2) Applicants for supplemental type certificates and for
amendments to type certificates: Before March 21, 2011 or before the
certificate is issued, whichever occurs later.

                                 Table 1
------------------------------------------------------------------------

-------------------------------------------------------------------------
                              Model--Boeing
------------------------------------------------------------------------
747 Series
737 Series
777 Series
767 Series
757 Series
------------------------------------------------------------------------
                              Model--Airbus
------------------------------------------------------------------------
A318, A319, A320, A321 Series
A300, A310 Series
A330, A340 Series
------------------------------------------------------------------------

    (d) Design Changes and Service Instructions. By the times specified
in paragraph (e) of this section, each person subject to this section
must meet the requirements of paragraphs (d)(1) or (d)(2) of this
section, as applicable.
    (1) For holders and applicants subject to paragraph (a)(1) or
(a)(3)(iii) of this section, if the assessment required by paragraph
(c) of this section identifies any features of the design change that
compromise any CDCCL applicable to any airplane on which the design
change is eligible for installation, the holder or applicant must
submit for approval by the FAA Oversight Office design changes and
service instructions for Flammability Impact Mitigation Means (FIMM)
that would bring the design change into compliance with the CDCCL. Any
fuel tank modified as required by this paragraph must also be evaluated
as required by paragraph (b) of this section.
    (2) Applicants subject to paragraph (a)(2), or (a)(3)(i) of this
section must comply with the requirements of 14 CFR 25.981, in effect
on September 19, 2008.
    (3) Applicants subject to paragraph (a)(3)(ii) of this section must
comply with the requirements of 14 CFR 26.33.
    (e) Compliance Times for Design Changes and Service Instructions.
The following persons subject to this section must comply with the
requirements of paragraph (d) of this section at the specified times.
    (1) Holders of supplemental type certificates and field approvals:
Before September 19, 2012.
    (2) Applicants for supplemental type certificates and for
amendments to type certificates: Before September 19, 2012, or before
the certificate is issued, whichever occurs later.
    (f) Compliance Planning. By the applicable date specified in Table
2 of this section, each person subject to paragraph (a)(1) of this
section must submit for approval by the FAA Oversight Office compliance
plans for the flammability exposure analysis required by paragraph (b)
of this section, the impact assessment required by paragraph (c) of
this section, and the design changes and service instructions required
by paragraph (d) of this section. Each person's compliance plans must
include the following:
    (1) A proposed project schedule for submitting the required
analysis or impact assessment.
    (2) A proposed means of compliance with paragraph (d) of this
section.
    (3) For the requirements of paragraph (d) of this section, a
proposal for submitting a draft of all design changes, if any are
required, and Airworthiness Limitations (including CDCCLs) for review
by the FAA Oversight Office not less than 60 days before the compliance
time specified in paragraph (e) of this section.
    (4) For the requirements of paragraph (d) of this section, a
proposal for how the approved service information and any necessary
modification parts will be made available to affected persons.

[[Page 42501]]



                                       Table 2.--Compliance Planning Dates
----------------------------------------------------------------------------------------------------------------
                                                                                            Design changes and
                                        Flammability exposure    Impact assessment plan   service  instructions
                                            analysis plan                                          plan
----------------------------------------------------------------------------------------------------------------
STC and Field Approval Holders.......  December 18, 2008......  November 19, 2010......  May 19, 2011.
----------------------------------------------------------------------------------------------------------------

    (g) Each person subject to this section must implement the
compliance plans, or later revisions, as approved under paragraph (f)
of this section.


Sec.  26.37  Pending type certification projects: Fuel tank
flammability.

    (a) Applicability. This section applies to any new type certificate
for a transport category airplane, if the application was made before
September 19, 2008, and if the certificate was not issued September 19,
2008. This section applies only if the airplane would have--
    (1) A maximum type-certificated passenger capacity of 30 or more,
or
    (2) A maximum payload capacity of 7,500 pounds or more.
    (b) If the application was made on or after June 6, 2001, the
requirements of 14 CFR 25.981 in effect on September 19, 2008, apply.


Sec.  26.39  Newly produced airplanes: Fuel tank flammability.

    (a) Applicability: This section applies to Boeing model airplanes
specified in Table 1 of this section, including passenger and cargo
versions of each model, when application is made for original
certificates of airworthiness or export airworthiness approvals after
September 20, 2010.

                                 Table 1
------------------------------------------------------------------------
                              Model--Boeing
-------------------------------------------------------------------------
747 Series
737 Series
777 Series
767 Series
------------------------------------------------------------------------

    (b) Any fuel tank meeting all of the criteria stated in paragraphs
(b)(1), (b)(2) and (b)(3) of this section must have flammability
reduction means (FRM) or ignition mitigation means (IMM) that meet the
requirements of 14 CFR 25.981 in effect on September 19, 2008.
    (1) The fuel tank is Normally Emptied.
    (2) Any portion of the fuel tank is located within the fuselage
contour.
    (3) The fuel tank exceeds a Fleet Average Flammability Exposure of
7 percent.
    (c) All other fuel tanks that exceed an Fleet Average Flammability
Exposure of 7 percent must have an IMM that meets 14 CFR 25.981(d) in
effect on September 19, 2008, or an FRM that meets all of the
requirements of Appendix M to this part, except instead of complying
with paragraph M25.1 of that appendix, the Fleet Average Flammability
Exposure may not exceed 7 percent.

PART 121--OPERATING REQUIREMENTS: DOMESTIC, FLAG, AND SUPPLEMENTAL
OPERATIONS

0
9. The authority citation for part 121 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 40119, 41706, 44101, 44701-
44702, 44705, 44709-44711, 44713, 44716-44717, 44722, 44901, 44903-
44904, 44012, 46105, 46301.


0
10. Amend part 121 by adding a new Sec.  121.1117, to read as follows:


Sec.  121.1117  Flammability reduction means.

    (a) Applicability. Except as provided in paragraph (o) of this
section, this section applies to transport category, turbine-powered
airplanes with a type certificate issued after January 1, 1958, that,
as a result of original type certification or later increase in
capacity have:
    (1) A maximum type-certificated passenger capacity of 30 or more,
or
    (2) A maximum payload capacity of 7,500 pounds or more.
    (b) New Production Airplanes. Except in accordance with Sec.
121.628, no certificate holder may operate an airplane identified in
Table 1 of this section (including all-cargo airplanes) for which the
State of Manufacture issued the original certificate of airworthiness
or export airworthiness approval after September 20, 2010 unless an
Ignition Mitigation Means (IMM) or Flammability Reduction Means (FRM)
meeting the requirements of Sec.  26.33 of this chapter is operational.

                                 Table 1
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A330, A340 Series
777 Series
767 Series
------------------------------------------------------------------------

    (c) Auxiliary Fuel Tanks. After the applicable date stated in
paragraph (e) of this section, no certificate holder may operate any
airplane subject to Sec.  26.33 of this chapter that has an Auxiliary
Fuel Tank installed pursuant to a field approval, unless the following
requirements are met:
    (1) The certificate holder complies with 14 CFR 26.35 by the
applicable date stated in that section.
    (2) The certificate holder installs Flammability Impact Mitigation
Means (FIMM), if applicable, that is approved by the FAA Oversight
Office.
    (3) Except in accordance with Sec.  121.628, the FIMM, if
applicable, is operational.
    (d) Retrofit. Except as provided in paragraphs (j), (k), and (l) of
this section, after the dates specified in paragraph (e) of this
section, no certificate holder may operate an airplane to which this
section applies unless the requirements of paragraphs (d)(1) and (d)(2)
of this section are met.
    (1) IMM, FRM or FIMM, if required by Sec. Sec.  26.33, 26.35, or
26.37 of this chapter, that are approved by the FAA Oversight Office,
are installed within the compliance times specified in paragraph (e) of
this section.
    (2) Except in accordance with Sec.  121.628, the IMM, FRM or FIMM,
as applicable, are operational.
    (e) Compliance Times. Except as provided in paragraphs (k) and (l)
of this section, the installations required by paragraph (d) of this
section must be accomplished no later than the applicable dates
specified in paragraph (e)(1), (e)(2), or (e)(3) of this section.
    (1) Fifty percent of each certificate holder's fleet identified in
paragraph (d)(1) of this section must be modified no later than
September 19, 2014.
    (2) One hundred percent of each certificate holder's fleet
identified in paragraph (d)(1) of this section must be modified no
later than September 19, 2017.
    (3) For those certificate holders that have only one airplane of a
model identified in Table 1 of this section, the airplane must be
modified no later than September 19, 2017.
    (f) Compliance After Installation. Except in accordance with Sec.
121.628, no certificate holder may--
    (1) Operate an airplane on which IMM or FRM has been installed
before the dates specified in paragraph (e) of this section unless the
IMM or FRM is operational, or
    (2) Deactivate or remove an IMM or FRM once installed unless it is
replaced

[[Page 42502]]

by a means that complies with paragraph (d) of this section.
    (g) Maintenance Program Revisions. No certificate holder may
operate an airplane for which airworthiness limitations have been
approved by the FAA Oversight Office in accordance with Sec. Sec.
26.33, 26.35, or 26.37 of this chapter after the airplane is modified
in accordance with paragraph (d) of this section unless the maintenance
program for that airplane is revised to include those applicable
airworthiness limitations.
    (h) After the maintenance program is revised as required by
paragraph (g) of this section, before returning an airplane to service
after any alteration for which airworthiness limitations are required
by Sec. Sec.  25.981, 26.33, or 26.37 of this chapter, the certificate
holder must revise the maintenance program for the airplane to include
those airworthiness limitations.
    (i) The maintenance program changes identified in paragraphs (g)
and (h) of this section must be submitted to the operator's Principal
Maintenance Inspector responsible for review and approval prior to
incorporation.
    (j) The requirements of paragraph (d) of this section do not apply
to airplanes operated in all-cargo service, but those airplanes are
subject to paragraph (f) of this section.
    (k) The compliance dates specified in paragraph (e) of this section
may be extended by one year, provided that--
    (1) No later than December 18, 2008, the certificate holder
notifies its assigned Flight Standards Office or Principal Inspector
that it intends to comply with this paragraph;
    (2) No later than March 18, 2009, the certificate holder applies
for an amendment to its operations specification in accordance with
Sec.  119.51 of this chapter and revises the manual required by Sec.
121.133 to include a requirement for the airplane models specified in
Table 2 of this section to use ground air conditioning systems for
actual gate times of more than 30 minutes, when available at the gate
and operational, whenever the ambient temperature exceeds 60 degrees
Fahrenheit; and
    (3) Thereafter, the certificate holder uses ground air conditioning
systems as described in paragraph (k)(2) of this section on each
airplane subject to the extension.

                                 Table 2
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A300, A310 Series
777 Series                                  A330, A340 Series
767 Series
757 Series
------------------------------------------------------------------------

    (l) For any certificate holder for which the operating certificate
is issued after September 19, 2008, the compliance date specified in
paragraph (e) of this section may be extended by one year, provided
that the certificate holder meets the requirements of paragraph (k)(2)
of this section when its initial operations specifications are issued
and, thereafter, uses ground air conditioning systems as described in
paragraph (k)(2) of this section on each airplane subject to the
extension.
    (m) After the date by which any person is required by this section
to modify 100 percent of the affected fleet, no certificate holder may
operate in passenger service any airplane model specified in Table 2 of
this section unless the airplane has been modified to comply with Sec.
26.33(c) of this chapter.
    (n) No certificate holder may operate any airplane on which an
auxiliary fuel tank is installed after September 19, 2017 unless the
FAA has certified the tank as compliant with Sec.  25.981 of this
chapter, in effect on September 19, 2008.
    (o) Exclusions. The requirements of this section do not apply to
the following airplane models:
    (1) Convair CV-240, 340, 440, including turbine powered
conversions.
    (2) Lockheed L-188 Electra.
    (3) Vickers Armstrong Viscount.
    (4) Douglas DC-3, including turbine powered conversions.
    (5) Bombardier CL-44.
    (6) Mitsubishi YS-11.
    (7) BAC 1-11.
    (8) Concorde.
    (9) deHavilland D.H. 106 Comet 4C.
    (10) VFW--Vereinigte Flugtechnische VFW-614.
    (11) Illyushin Aviation IL 96T.
    (12) Vickers Armstrong Viscount.
    (13) Bristol Aircraft Britannia 305.
    (14) Handley Page Handley Page Herald Type 300.
    (15) Avions Marcel Dassault--Breguet Aviation Mercure 100C.
    (16) Airbus Caravelle.
    (17) Fokker F-27/Fairchild Hiller FH-227.
    (18) Lockheed L-300.

PART 125--CERTIFICATION AND OPERATIONS; AIRPLANES HAVING A SEATING
CAPACITY OF 20 OR MORE PASSENGERS OR A MAXIMUM PAYLOAD CAPACITY OF
6,000 POUNDS OR MORE; AND RULES GOVERNING PERSONS ON BOARD SUCH
AIRCRAFT

0
11. The authority citation for part 125 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44705, 44710-
44711, 44713, 44716-44717, 44722.


0
12. Amend part 125 by adding a new Sec.  125.509 to read as follows:


Sec.  125.509  Flammability reduction means.

    (a) Applicability. Except as provided in paragraph (m) of this
section, this section applies to transport category, turbine-powered
airplanes with a type certificate issued after January 1, 1958, that,
as a result of original type certification or later increase in
capacity have:
    (1) A maximum type-certificated passenger capacity of 30 or more,
or
    (2) A maximum payload capacity of 7,500 pounds or more.
    (b) New Production Airplanes. Except in accordance with Sec.
125.201, no person may operate an airplane identified in Table 1 of
this section (including all-cargo airplanes) for which the State of
Manufacture issued the original certificate of airworthiness or export
airworthiness approval after September 20, 2010 unless an Ignition
Mitigation Means (IMM) or Flammability Reduction Means (FRM) meeting
the requirements of Sec.  26.33 of this chapter is operational.

                                 Table 1
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A330, A340 Series
777 Series
767 Series
------------------------------------------------------------------------

    (c) Auxiliary Fuel Tanks. After the applicable date stated in
paragraph (e) of this section, no person may operate any airplane
subject to Sec.  26.33 of this chapter that has an Auxiliary Fuel Tank
installed pursuant to a field approval, unless the following
requirements are met:
    (1) The person complies with 14 CFR 26.35 by the applicable date
stated in that section.
    (2) The person installs Flammability Impact Mitigation Means
(FIMM), if applicable, that is approved by the FAA Oversight Office.

[[Page 42503]]

    (3) Except in accordance with Sec.  125.201, the FIMM, if
applicable, are operational.
    (d) Retrofit. Except as provided in paragraph (j) of this section,
after the dates specified in paragraph (e) of this section, no person
may operate an airplane to which this section applies unless the
requirements of paragraphs (d)(1) and (d)(2) of this section are met.
    (1) Ignition Mitigation Means (IMM), Flammability Reduction Means
(FRM), or FIMM, if required by Sec. Sec.  26.33, 26.35, or 26.37 of
this chapter, that are approved by the FAA Oversight Office, are
installed within the compliance times specified in paragraph (e) of
this section.
    (2) Except in accordance with Sec.  125.201 of this part, the IMM,
FRM or FIMM, as applicable, are operational.
    (e) Compliance Times. The installations required by paragraph (d)
of this section must be accomplished no later than the applicable dates
specified in paragraph (e)(1), (e)(2) or (e)(3) of this section.
    (1) Fifty percent of each person's fleet of airplanes subject to
paragraph (d)(1) of this section must be modified no later than
September 19, 2014.
    (2) One hundred percent of each person's fleet of airplanes subject
to paragraph (d)(1) of this section must be modified no later than
September 19, 2017.
    (3) For those persons that have only one airplane of a model
identified in Table 1 of this section, the airplane must be modified no
later than September 19, 2017.
    (f) Compliance after Installation. Except in accordance with Sec.
125.201, no person may--
    (1) Operate an airplane on which IMM or FRM has been installed
before the dates specified in paragraph (e) of this section unless the
IMM or FRM is operational, or
    (2) Deactivate or remove an IMM or FRM once installed unless it is
replaced by a means that complies with paragraph (d) of this section.
    (g) Inspection Program Revisions. No person may operate an airplane
for which airworthiness limitations have been approved by the FAA
Oversight Office in accordance with Sec. Sec.  26.33, 26.35, or 26.37
of this chapter after the airplane is modified in accordance with
paragraph (d) of this section unless the inspection program for that
airplane is revised to include those applicable airworthiness
limitations.
    (h) After the inspection program is revised as required by
paragraph (g) of this section, before returning an airplane to service
after any alteration for which airworthiness limitations are required
by Sec. Sec.  25.981, 26.33, 26.35, or 26.37 of this chapter, the
person must revise the inspection program for the airplane to include
those airworthiness limitations.
    (i) The inspection program changes identified in paragraphs (g) and
(h) of this section must be submitted to the operator's assigned Flight
Standards Office responsible for review and approval prior to
incorporation.
    (j) The requirements of paragraph (d) of this section do not apply
to airplanes operated in all-cargo service, but those airplanes are
subject to paragraph (f) of this section.
    (k) After the date by which any person is required by this section
to modify 100 percent of the affected fleet, no person may operate in
passenger service any airplane model specified in Table 2 of this
section unless the airplane has been modified to comply with Sec.
26.33(c) of this chapter.
    (l) No person may operate any airplane on which an auxiliary fuel
tank is installed after September 19, 2017 unless the FAA has certified
the tank as compliant with Sec.  25.981 of this chapter, in effect on
September 19, 2008.
    (m) Exclusions. The requirements of this section do not apply to
the following airplane models:
    (1) Convair CV-240, 340, 440, including turbine powered
conversions.
    (2) Lockheed L-188 Electra.
    (3) Vickers Armstrong Viscount.
    (4) Douglas DC-3, including turbine powered conversions.
    (5) Bombardier CL-44.
    (6) Mitsubishi YS-11.
    (7) BAC 1-11.
    (8) Concorde.
    (9) deHavilland D.H. 106 Comet 4C.
    (10) VFW--Vereinigte Flugtechnische VFW-614.
    (11) Illyushin Aviation IL 96T.
    (12) Vickers Armstrong Viscount.
    (13) Bristol Aircraft Britannia 305.
    (14) Handley Page Handley Page Herald Type 300.
    (15) Avions Marcel Dassault--Breguet Aviation Mercure 100C.
    (16) Airbus Caravelle.
    (17) Fokker F-27/Fairchild Hiller FH-227.
    (18) Lockheed L-300.

PART 129--OPERATIONS: FOREIGN AIR CARRIERS AND FOREIGN OPERATORS OF
U.S.-REGISTERED AIRCRAFT ENGAGED IN COMMON CARRIAGE

0
13. The authority citation for part 129 continues to read as follows:

    Authority: 49 U.S.C. 1372, 49113, 440119, 44101, 44701-44702,
447-5, 44709-44711, 44713, 44716-44717, 44722, 44901-44904, 44906,
44912, 44105, Pub. L. 107-71 sec. 104.


0
14. Amend part 129 by adding a new Sec.  129.117 to read as follows:


Sec.  129.117  Flammability reduction means.

    (a) Applicability. Except as provided in paragraph (o) of this
section, this section applies to U.S.-registered transport category,
turbine-powered airplanes with a type certificate issued after January
1, 1958, that as a result of original type certification or later
increase in capacity have:
    (1) A maximum type-certificated passenger capacity of 30 or more,
or
    (2) A maximum payload capacity of 7,500 pounds or more.
    (b) New Production Airplanes. Except in accordance with Sec.
129.14, no foreign air carrier or foreign person may operate an
airplane identified in Table 1 of this section (including all-cargo
airplanes) for which application is made for original certificate of
airworthiness or export airworthiness approval after September 20, 2010
unless an Ignition Mitigation Means (IMM) or Flammability Reduction
Means (FRM) meeting the requirements of Sec.  26.33 of this chapter is
operational.

                                 Table 1
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A330, A340 Series
777 Series
767 Series
------------------------------------------------------------------------

    (c) Auxiliary Fuel Tanks. After the applicable date stated in
paragraph (e) of this section, no foreign air carrier or foreign person
may operate any airplane subject Sec.  26.33 of this chapter that has
an Auxiliary Fuel Tank installed pursuant to a field approval, unless
the following requirements are met:
    (1) The foreign air carrier or foreign person complies with 14 CFR
26.35 by the applicable date stated in that section.
    (2) The foreign air carrier or foreign person installs Flammability
Impact Mitigation Means (FIMM), if applicable, that are approved by the
FAA Oversight Office.
    (3) Except in accordance with Sec.  129.14, the FIMM, if
applicable, are operational.
    (d) Retrofit. After the dates specified in paragraphs (j), (k), and
(l) of this section, after the dates specified in paragraph (e) of this
section, no foreign air carrier or foreign person may operate an
airplane to which this section applies unless the requirements of
paragraphs (d)(1) and (d)(2) of this section are met.
    (1) IMM, FRM or FIMM, if required by Sec. Sec.  26.33, 26.35, or
26.37 of this chapter,

[[Page 42504]]

that are approved by the FAA Oversight Office, are installed within the
compliance times specified in paragraph (e) of this section.
    (2) Except in accordance with Sec.  129.14, the IMM, FRM or FIMM,
as applicable, are operational.
    (e) Compliance Times. Except as provided in paragraphs (k) and (l)
of this section, the installations required by paragraph (d) of this
section must be accomplished no later than the applicable dates
specified in paragraph (e)(1) or (e)(2) of this section.
    (1) Fifty percent of each foreign air carrier or foreign person's
fleet identified in paragraph (d)(1) of this section must be modified
no later than September 19, 2014.
    (2) One hundred percent of each foreign air carrier or foreign
person's fleet of airplanes subject to paragraph (d)(1) or this section
must be modified no later than September 19, 2017.
    (3) For those foreign air carriers or foreign persons that have
only one airplane for a model identified in Table 1, the airplane must
be modified no later than September 19, 2017.
    (f) Compliance after Installation. Except in accordance with Sec.
129.14, no person may--
    (1) Operate an airplane on which IMM or FRM has been installed
before the dates specified in paragraph (e) of this section unless the
IMM or FRM is operational.
    (2) Deactivate or remove an IMM or FRM once installed unless it is
replaced by a means that complies with paragraph (d) of this section.
    (g) Maintenance Program Revisions. No foreign air carrier or
foreign person may operate an airplane for which airworthiness
limitations have been approved by the FAA Oversight Office in
accordance with Sec. Sec.  26.33, 26.35, or 26.37 of this chapter after
the airplane is modified in accordance with paragraph (d) of this
section unless the maintenance program for that airplane is revised to
include those applicable airworthiness limitations.
    (h) After the maintenance program is revised as required by
paragraph (g) of this section, before returning an airplane to service
after any alteration for which airworthiness limitations are required
by Sec. Sec.  25.981, 26.33, 26.35, or 26.37 of this chapter, the
foreign person or foreign air carrier must revise the maintenance
program for the airplane to include those airworthiness limitations.
    (i) The maintenance program changes identified in paragraphs (g)
and (h) of this section must be submitted to the operator's assigned
Flight Standards Office or Principal Inspector for review and approval
prior to incorporation.
    (j) The requirements of paragraph (d) of this section do not apply
to airplanes operated in all-cargo service, but those airplanes are
subject to paragraph (f) of this section.
    (k) The compliance dates specified in paragraph (e) of this section
may be extended by one year, provided that--
    (1) No later than December 18, 2008, the foreign air carrier or
foreign person notifies its assigned Flight Standards Office or
Principal Inspector that it intends to comply with this paragraph;
    (2) No later than March 18, 2009, the foreign air carrier or
foreign person applies for an amendment to its operations
specifications in accordance with Sec.  129.11 to include a requirement
for the airplane models specified in Table 2 of this section to use
ground air conditioning systems for actual gate times of more than 30
minutes, when available at the gate and operational, whenever the
ambient temperature exceeds 60 degrees Fahrenheit; and
    (3) Thereafter, the certificate holder uses ground air conditioning
systems as described in paragraph (k)(2) of this section on each
airplane subject to the extension.

                                 Table 2
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A300, A310 Series
777 Series                                  A330, A340 Series
767 Series
757 Series
------------------------------------------------------------------------

    (l) For any foreign air carrier or foreign person for which the
operating certificate is issued after September 19, 2008, the
compliance date specified in paragraph (e) of this section may be
extended by one year, provided that the foreign air carrier or foreign
person meets the requirements of paragraph (k)(2) of this section when
its initial operations specifications are issued and, thereafter, uses
ground air conditioning systems as described in paragraph (k)(2) of
this section on each airplane subject to the extension.
    (m) After the date by which any person is required by this section
to modify 100 percent of the affected fleet, no person may operate in
passenger service any airplane model specified in Table 2 of this
section unless the airplane has been modified to comply with Sec.
26.33(c) of this chapter.

                                 Table 3
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A300, A310 Series
777 Series                                  A330, A340 Series
767 Series
757 Series
707/720 Series
------------------------------------------------------------------------

    (n) No foreign air carrier or foreign person may operate any
airplane on which an auxiliary fuel tank is installed after September
19, 2017 unless the FAA has certified the tank as compliant with Sec.
25.981 of this chapter, in effect on September 19, 2008.
    (o) Exclusions. The requirements of this section do not apply to
the following airplane models:
    (1) Convair CV-240, 340, 440, including turbine powered
conversions.
    (2) Lockheed L-188 Electra.
    (3) Vickers Armstrong Viscount.
    (4) Douglas DC-3, including turbine powered conversions.
    (5) Bombardier CL-44.
    (6) Mitsubishi YS-11.
    (7) BAC 1-11.
    (8) Concorde.
    (9) deHavilland D.H. 106 Comet 4C.
    (10) VFW--Vereinigte Flugtechnische VFW-614.
    (11) Illyushin Aviation IL 96T.
    (12) Vickers Armstrong Viscount.
    (13) Bristol Aircraft Britannia 305.
    (14) Handley Page Handley Page Herald Type 300.
    (15) Avions Marcel Dassault--Breguet Aviation Mercure 100C.
    (16) Airbus Caravelle.
    (17) Fokker F-27/Fairchild Hiller FH-227.
    (18) Lockheed L-300.

    Issued in Washington, DC, on July 9, 2008.
Robert A. Sturgell,
Acting Administrator.
[FR Doc. E8-16084 Filed 7-16-08; 10:30 am]

BILLING CODE 4910-13-P
