
[Federal Register: March 11, 2008 (Volume 73, Number 48)]
[Proposed Rules]               
[Page 12910-12912]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr11mr08-20]                         

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2008-0269; Directorate Identifier 2007-NM-320-AD]
RIN 2120-AA64

 
Airworthiness Directives; Boeing Model 737-600, -700, -700C, -
800, and -900 Series Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: We propose to adopt a new airworthiness directive (AD) for 
certain Boeing Model 737-600, -700, -700C, -800, and -900 series 
airplanes. This proposed AD would require replacement of the power 
control relays in the P91 and P92 power distribution panels for the 
fuel boost and override pumps with new improved relays. This proposed 
AD would also require a revision to the Airworthiness Limitations 
(AWLs) section of the Instructions for Continued Airworthiness to 
incorporate AWL No. 28-AWL-20. This proposed AD results from fuel 
system reviews conducted by the manufacturer. We are proposing this AD 
to prevent pump housing burn-through due to electrical arcing, which 
could create a potential ignition source inside a fuel tank. This 
condition, in combination with flammable fuel vapors, could result in a 
fuel tank explosion and consequent loss of the airplane.

DATES: We must receive comments on this proposed AD by April 25, 2008.

ADDRESSES: You may send comments by any of the following methods:
     Federal eRulemaking Portal: Go to http://
www.regulations.gov. Follow the instructions for submitting comments.
     Fax: 202-493-2251.
     Mail: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue, SE., Washington, DC 20590.
     Hand Delivery: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue, SE., Washington, DC 20590, between 9 a.m. and 5 p.m., 
Monday through Friday, except Federal holidays.
    For service information identified in this AD, contact Boeing 
Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207.

Examining the AD Docket

    You may examine the AD docket on the Internet at http://
www.regulations.gov; or in person at the Docket Management Facility 
between 9 a.m. and 5 p.m., Monday through Friday, except Federal 
holidays. The AD docket contains this proposed AD, the regulatory 
evaluation, any comments received, and other information. The street 
address for the Docket Office (telephone 800-647-5527) is in the 
ADDRESSES section. Comments will be available in the AD docket shortly 
after receipt.

FOR FURTHER INFORMATION CONTACT: Jen Pei, Aerospace Engineer, Systems 
and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification 
Office, 1601 Lind Avenue SW., Renton, Washington 98057-3356; telephone 
(425) 917-6409; fax (425) 917-6590.

SUPPLEMENTARY INFORMATION: 

Comments Invited

    We invite you to send any written relevant data, views, or 
arguments about this proposed AD. Send your comments to an address 
listed under the ADDRESSES section. Include ``Docket No. FAA-2008-0269; 
Directorate Identifier 2007-NM-320-AD'' at the beginning of your 
comments. We specifically invite comments on the overall regulatory, 
economic, environmental, and energy aspects of this proposed AD. We 
will consider all comments received by the closing date and may amend 
this proposed AD because of those comments.

[[Page 12911]]

    We will post all comments we receive, without change, to http://
www.regulations.gov, including any personal information you provide. We 
will also post a report summarizing each substantive verbal contact we 
receive about this proposed AD.

Discussion

    The FAA has examined the underlying safety issues involved in fuel 
tank explosions on several large transport airplanes, including the 
adequacy of existing regulations, the service history of airplanes 
subject to those regulations, and existing maintenance practices for 
fuel tank systems. As a result of those findings, we issued a 
regulation titled ``Transport Airplane Fuel Tank System Design Review, 
Flammability Reduction and Maintenance and Inspection Requirements'' 
(66 FR 23086, May 7, 2001). In addition to new airworthiness standards 
for transport airplanes and new maintenance requirements, this rule 
included Special Federal Aviation Regulation No. 88 (``SFAR 88,'' 
Amendment 21-78, and subsequent Amendments 21-82 and 21-83).
    Among other actions, SFAR 88 requires certain type design (i.e., 
type certificate (TC) and supplemental type certificate (STC)) holders 
to substantiate that their fuel tank systems can prevent ignition 
sources in the fuel tanks. This requirement applies to type design 
holders for large turbine-powered transport airplanes and for 
subsequent modifications to those airplanes. It requires them to 
perform design reviews and to develop design changes and maintenance 
procedures if their designs do not meet the new fuel tank safety 
standards. As explained in the preamble to the rule, we intended to 
adopt airworthiness directives to mandate any changes found necessary 
to address unsafe conditions identified as a result of these reviews.
    In evaluating these design reviews, we have established four 
criteria intended to define the unsafe conditions associated with fuel 
tank systems that require corrective actions. The percentage of 
operating time during which fuel tanks are exposed to flammable 
conditions is one of these criteria. The other three criteria address 
the failure types under evaluation: single failures, single failures in 
combination with a latent condition(s), and in-service failure 
experience. For all four criteria, the evaluations included 
consideration of previous actions taken that may mitigate the need for 
further action.
    We have determined that the actions identified in this AD are 
necessary to reduce the potential of ignition sources inside fuel 
tanks, which, in combination with flammable fuel vapors, could result 
in fuel tank explosions and consequent loss of the airplane.
    The power control relays for the fuel boost and override pumps must 
be replaced with new relays that include a ground fault interrupter 
(GFI) feature. The GFI is designed to detect electrical faults and open 
the circuit prior to pump housing burn-through. Burn-through due to 
electrical arcing could create a potential ignition source inside the 
center fuel tank. This condition in combination with flammable fuel 
vapors, if not corrected, could result in a fuel tank explosion and 
consequent loss of the airplane.

Relevant Service Information

    We have reviewed Boeing Alert Service Bulletin 737-28A1201, dated 
February 19, 2007. The service bulletin describes procedures for 
replacing the power control relays in the P91 and P92 power 
distribution panels for the fuel boost and override pumps with new, 
improved relays having a GFI feature.
    The Boeing service bulletin refers to Honeywell Service Bulletin 
1151932-24-61, dated November 10, 2006, as an additional source of 
service information for replacing the power control relays in the P91 
power distribution panel. The Boeing service bulletin also refers to 
Honeywell Service Bulletin 1151934-24-62, dated November 10, 2006, as 
an additional source of service information for replacing the power 
control relays in the P92 power distribution panels.
    We have also reviewed Section 9 of the Boeing 737-600/700/800/900 
Maintenance Planning Data (MPD) Document, D626A001-CMR, Revision March 
2007 R2 (hereafter referred to as ``Revision March 2007 of the MPD''). 
Subsection F, ``AIRWORTHINESS LIMITATIONS--FUEL SYSTEMS AWLs,'' of 
Revision March 2007 of the MPD describes new airworthiness limitations 
(AWLs) for fuel tank systems. Subsection F of Revision March 2007 of 
the MPD adds new fuel system AWL No. 28-AWL-20, which is a repetitive 
operational check of the GFI for all alternating current fuel tank 
boost pumps to ensure continued functionality of the GFI circuit.

FAA's Determination and Requirements of This Proposed AD

    We are proposing this AD because we evaluated all relevant 
information and determined the unsafe condition described previously is 
likely to exist or develop in other products of the(se) same type 
design(s). This proposed AD would require the following actions:
     Replacement of the power control relays in the P91 and P92 
power distribution panels for the fuel boost and override pumps with 
new, improved relays having a GFI feature.
     Revision to the AWLs section of the Instructions for 
Continued Airworthiness to incorporate AWL No. 28-AWL-20, which would 
require repetitive operational checks of the GFI for all alternating 
current fuel tank boost pumps to ensure continued functionality.
    This proposed AD would also allow accomplishing the revision to the 
AWLs section of the Instructions for Continued Airworthiness in 
accordance with later revisions of the MPD as an acceptable method of 
compliance if they are approved by the Manager, Seattle Aircraft 
Certification Office, FAA.

Costs of Compliance

    We estimate that this proposed AD would affect 754 aircraft of U.S. 
registry. The following table provides the estimated costs, at an 
average labor rate of $80 per hour, for U.S. operators to comply with 
this proposed AD.

                                                 Estimated Costs
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                                                                                       Cost per
                 Action                    Work hours               Parts              product      Fleet cost
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Installation of GFI relays.............               8  $11,010...................      $11,650      $8,784,100
Maintenance program revision...........               1  None......................          $80         $60,320
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[[Page 12912]]

Authority for This Rulemaking

    Title 49 of the United States Code specifies the FAA's authority to 
issue rules on aviation safety. 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.
    We are issuing this rulemaking under the authority described in 
``Subtitle VII, Part A, Subpart III, Section 44701: General 
requirements.'' Under that section, Congress charges the FAA with 
promoting safe flight of civil aircraft in air commerce by prescribing 
regulations for practices, methods, and procedures the Administrator 
finds necessary for safety in air commerce. This regulation is within 
the scope of that authority because it addresses an unsafe condition 
that is likely to exist or develop on products identified in this 
rulemaking action.

Regulatory Findings

    We determined that this proposed AD would not have federalism 
implications under Executive Order 13132. This proposed AD would 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.
    For the reasons discussed above, I certify this proposed 
regulation:
    1. Is not a ``significant regulatory action'' under Executive Order 
12866,
    2. Is not a ``significant rule'' under the DOT Regulatory Policies 
and Procedures (44 FR 11034, February 26, 1979), and
    3. Will not have a significant economic impact, positive or 
negative, on a substantial number of small entities under the criteria 
of the Regulatory Flexibility Act.
    You can find our regulatory evaluation and the estimated costs of 
compliance in the AD Docket.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

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


Sec.  39.13  [Amended]

    2. The FAA amends Sec.  39.13 by adding the following new AD:

Boeing: Docket No. FAA-2008-0269; Directorate Identifier 2007-NM-
320-AD.

Comments Due Date

    (a) We must receive comments by April 25, 2008.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Boeing Model 737-600, -700, -700C, -800, 
and -900 series airplanes, certificated in any category; as 
identified in Boeing Alert Service Bulletin 737-28A1201, dated 
February 19, 2007.


    Note 1: This AD requires revisions to certain operator 
maintenance documents to include new inspections. Compliance with 
these inspections is required by 14 CFR 91.403(c). For airplanes 
that have been previously modified, altered, or repaired in the 
areas addressed by these inspections, the operator may not be able 
to accomplish the inspections described in the revisions. In this 
situation, to comply with 14 CFR 91.403(c), the operator must 
request approval for an alternative method of compliance (AMOC) 
according to paragraph (i) of this AD. The request should include a 
description of changes to the required inspections that will ensure 
the continued operational safety of the airplane.

Unsafe Condition

    (d) This AD results from fuel system reviews conducted by the 
manufacturer. We are issuing this AD to prevent pump housing burn-
through due to electrical arcing, which could create a potential 
ignition source inside a fuel tank. This condition, in combination 
with flammable fuel vapors, could result in a fuel tank explosion 
and consequent loss of the airplane.

Compliance

    (e) Comply with this AD within the compliance times specified, 
unless already done.

Replacement

    (f) Within 60 months after the effective date of this AD, 
replace the power control relays in the P91 and P92 power 
distribution panels for the fuel boost and override pumps with new 
improved relays having a ground fault interrupter (GFI) feature, in 
accordance with the Accomplishment Instructions of the service 
bulletin.


    Note 2: The Boeing service bulletin refers to Honeywell Service 
Bulletin 1151932-24-61 and Honeywell Service Bulletin 1151934-24-62, 
both dated November 10, 2006, as additional sources of service 
information for replacement of the power control relays in the P91 
and P92 power distribution panels.

Airworthiness Limitations (AWLs) Revision

    (g) Concurrently with accomplishing the actions specified in 
paragraph (f) of this AD, revise the AWLs section of the 
Instructions for Continued Airworthiness by incorporating AWL No. 
28-AWL-20 of Subsection F of the Boeing 737-600/700/800/900 
Maintenance Planning Data (MPD) Document, D626A001-CMR, Section 9, 
Revision March 2007 R2 (hereafter referred to as ``the MPD'').

No Alternative Inspections or Inspection Intervals

    (h) After accomplishing the action specified in paragraph (g) of 
this AD, no alternative inspections or inspection intervals may be 
used unless the inspections or intervals are part of a later 
revision of the MPD that is approved by the Manager, Seattle ACO; or 
unless the inspections or intervals are approved as an AMOC in 
accordance with the procedures specified in paragraph (j) of this 
AD.

Alternative Methods of Compliance (AMOCs)

    (i)(1) The Manager, Seattle ACO, FAA, ATTN: Jen Pei, Aerospace 
Engineer, Systems and Equipment Branch, ANM-130S, 1601 Lind Avenue, 
SW., Renton, Washington 98057-3356; telephone (425) 917-6409; fax 
(425) 917-6590; has the authority to approve AMOCs for this AD, if 
requested using the procedures found in 14 CFR 39.19.
    (2) To request a different method of compliance or a different 
compliance time for this AD, follow the procedures in 14 CFR 39.19. 
Before using any approved AMOC on any airplane to which the AMOC 
applies, notify your appropriate principal inspector (PI) in the FAA 
Flight Standards District Office (FSDO), or lacking a PI, your local 
FSDO.

    Issued in Renton, Washington, on March 3, 2008.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
 [FR Doc. E8-4773 Filed 3-10-08; 8:45 am]

BILLING CODE 4910-13-P
