
[Federal Register Volume 88, Number 237 (Tuesday, December 12, 2023)]
[Proposed Rules]
[Pages 86080-86084]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-27101]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2023-2235; Project Identifier AD-2023-01009-T]
RIN 2120-AA64


Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD) 
for certain The Boeing Company Model 737-600, -700, -700C, -800, -900, 
and -900ER series airplanes. This proposed AD was prompted by two 
engine fan blade-out (FBO) events that resulted in the separation of 
engine inlet cowl and fan cowl parts from the airplane damaging the 
fuselage, which caused loss of pressurization and subsequent emergency 
descent. The FBO events also resulted in cracks in the primary exhaust 
nozzle, potentially resulting in the departure of the primary exhaust 
nozzle and damaging a stabilizer or striking the fuselage and window. 
This proposed AD would require an inspection or maintenance records 
check to determine if the primary exhaust nozzle has an affected part 
number and, for affected primary exhaust nozzles, an installation of 
bridge brackets onto the primary exhaust nozzle, or as an option, an 
installation of a serviceable primary exhaust nozzle. This proposed AD 
would also require revising the existing maintenance or inspection 
program, as applicable, to incorporate new airworthiness limitations. 
The FAA is proposing this AD to address the unsafe condition on these 
products.

DATES: The FAA must receive comments on this proposed AD by January 26, 
2024.

ADDRESSES: You may send comments, using the procedures found in 14 CFR 
11.43 and 11.45, by any of the following methods:
     Federal eRulemaking Portal: Go to 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: Deliver to Mail address above between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    AD Docket: You may examine the AD docket at regulations.gov under 
Docket No. FAA-2023-2235; or in person at Docket Operations between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD 
docket contains this NPRM, any comments received, and other 
information. The street address for Docket Operations is listed above.
    Material Incorporated by Reference:
     For service information identified in this NPRM, contact 
Boeing Commercial Airplanes, Attention: Contractual & Data Services 
(C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; 
telephone 562-797-1717; website myboeingfleet.com.
     You may view this service information at the FAA, 
Airworthiness Products Section, Operational Safety Branch, 2200 South 
216th St., Des Moines, WA. For information on the availability of this 
material at the FAA, call 206-231-3195. It is also available at 
regulations.gov by searching for and locating Docket No. FAA-2023-2235.

FOR FURTHER INFORMATION CONTACT: Luis Cortez-Muniz, Aviation Safety 
Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; telephone: 
206-231-3958; email: [email protected].

SUPPLEMENTARY INFORMATION: 

Comments Invited

    The FAA invites you to send any written relevant data, views, or 
arguments about this proposal. Send your comments to an address listed 
under ADDRESSES. Include ``Docket No. FAA-2023-2235; Project Identifier 
AD-2023-01009-T'' at the beginning of your comments. The most helpful 
comments reference a specific portion of the proposal, explain the 
reason for any recommended change, and include supporting data. The FAA 
will consider all comments received by the closing date and may amend 
this proposal because of those comments.
    Except for Confidential Business Information (CBI) as described in 
the following paragraph, and other information as described in 14 CFR 
11.35, the FAA will post all comments received, without change, to 
regulations.gov, including any personal information you provide. The 
agency will also post a report summarizing each substantive verbal 
contact received about this NPRM.

Confidential Business Information

    CBI is commercial or financial information that is both customarily 
and actually treated as private by its owner. Under the Freedom of 
Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public 
disclosure. If your comments responsive to this NPRM contain commercial 
or financial information that is customarily treated as private, that 
you actually treat as private, and that is relevant or responsive to 
this NPRM, it is important that you clearly designate the submitted 
comments as CBI. Please mark each page of your submission containing 
CBI as ``PROPIN.'' The FAA will treat such marked submissions as 
confidential under the FOIA, and they will not be placed in the public 
docket of this NPRM. Submissions containing CBI should be sent to Luis 
Cortez-Muniz, Aviation Safety Engineer, FAA, 2200 South 216th St., Des 
Moines, WA 98198; telephone: 206-231-3958; email: [email protected]. Any commentary that the FAA receives that

[[Page 86081]]

is not specifically designated as CBI will be placed in the public 
docket for this rulemaking.

Background

    The FAA received two reports of engine events that resulted in the 
separation of engine inlet cowl and fan cowl parts from the airplane. 
One event occurred in August 2016 on a Boeing Model 737-700 series 
airplane powered by a CFM56-7B engine. The left engine failed due to 
the FBO but the airplane landed successfully. The second event occurred 
on April 17, 2018, on a Boeing Model 737-700 series airplane powered by 
a CFM56-7B engine. In that event, an FBO occurrence resulted in the 
release of fan cowl parts and the engine cowling departing the 
airplane. The fan cowl parts damaged the fuselage, which caused loss of 
pressurization and subsequent emergency descent. Although the airplane 
landed safely, there was one passenger fatality. In that event, the 
suspected cause of the FBO occurrence was a low-cycle fatigue crack in 
the dovetail of fan blade number 13 of engine number 1. The broken fan 
blade hit the engine fan case at a critical location causing a 
significant impulse, displacement, and imbalance of the fan rotor 
effecting the structural integrity of the engine cowling.
    In response to these events, the FAA issued two AD actions for the 
CFM International S.A. (CFM) Model CFM56-7B engines. The FAA issued 
emergency AD 2018-09-51, Amendment 39-19287 (83 FR 23794, May 23, 2018) 
(AD 2018-09-51), which requires a one-time ultrasonic inspection of the 
concave and convex sides of the fan blade dovetail. The FAA also issued 
AD 2018-26-01, Amendment 39-19531 (83 FR 66090, December 26, 2018) (AD 
2018-26-01), which requires initial and repetitive inspections of the 
concave and convex sides of the fan blade dovetail to detect cracking 
and replacement of any blades found. The FAA issued AD 2018-09-51 to 
address fan blade failure due to cracking, which could result in an 
engine in-flight shutdown (IFSD), uncontained release of debris, damage 
to the engine, damage to the airplane, and possible airplane 
decompression. The FAA issued AD 2018-26-01 to address failure of the 
fan blade, which could result in the engine inlet cowl disintegrating 
and debris penetrating the fuselage, causing a loss of pressurization, 
and prompting an emergency descent.
    Since AD 2018-09-51 and AD 2018-26-01 were issued, the FAA has 
determined further rulemaking is necessary to reduce the probability of 
unsecured nacelle components, should an engine fan blade failure occur. 
As evidenced by Exemption No. 19212, dated July 13, 2022 (Docket No. 
FAA-2023-2235), Boeing developed modifications to the inlet cowl, fan 
cowl, and exhaust nozzle that must be accomplished prior to July 31, 
2028. Boeing petitioned and the FAA later agreed to amend Exemption No. 
19212 to 19212A, which added a requirement that solutions to address 
potential maintenance errors must be incorporated prior to December 31, 
2029. However, to implement these design changes, the FAA must issue 
rulemaking to address the unsafe condition.
    This proposed AD would address the unsafe condition related to the 
primary exhaust nozzle that was also a result of the FBO events. During 
an FBO event, primary exhaust nozzles that are not strengthened could 
depart the engine, potentially damaging a stabilizer or striking the 
fuselage and window. This condition, if not addressed, could result in 
loss of control of the airplane, or in a rapid decompression and hazard 
to window-seated passengers aft of the wing.

FAA's Determination

    The FAA is issuing this NPRM after determining that the unsafe 
condition described previously is likely to exist or develop on other 
products of the same type design.

Related Service Information Under 1 CFR Part 51

    The FAA reviewed Boeing Special Attention Requirements Bulletin 
737-78-1106 RB, dated September 1, 2023. This service information 
specifies procedures for a maintenance records check, or an inspection 
of the engine to identify if the engine has a primary exhaust nozzle 
with an affected part number. For affected primary exhaust nozzles, the 
service information specifies procedures for installing bridge brackets 
onto the primary exhaust nozzle, or as an option, installing a 
serviceable exhaust nozzle onto the engine.
    The service information also requires revision of the operator's 
maintenance or inspection program, as applicable, by incorporating 
certain airworthiness limitations (AWLs).
    This service information is reasonably available because the 
interested parties have access to it through their normal course of 
business or by the means identified in ADDRESSES.

Proposed AD Requirements in This NPRM

    This proposed AD would require accomplishing the actions specified 
in the service information already described, except as discussed under 
``Differences Between this Proposed AD and the Service Information'' 
and except for any differences identified as exceptions in the 
regulatory text of this proposed AD. For information on the procedures 
and compliance times, see this service information at regulations.gov 
under Docket No. FAA-2023-2235.
    This proposed AD would require revisions to certain operator 
maintenance documents to include new airworthiness limitations. 
Compliance with these limitations is required by 14 CFR 91.403(c). For 
airplanes that have been previously modified, altered, or repaired in 
the areas addressed by this proposed AD, the operator may not be able 
to accomplish the actions 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 according to paragraph 
(j) of this proposed AD.

Differences Between This Proposed AD and the Service Information

    The Effectivity of Boeing Special Attention Requirements Bulletin 
737-78-1106 RB inadvertently excluded Boeing Model 737-600, -700, -
700C, -800, -900, and -900ER series airplanes having line numbers 1245, 
1614, 1810, 1839, 1885, 1934, 1979, 1991, 2080, 2157, 2232, 2531, 2822, 
3071, 3189, and 3319. Those airplanes are affected by the identified 
unsafe condition; for those airplanes, this proposed AD would require 
accomplishment of the applicable actions specified in Boeing Special 
Attention Requirements Bulletin 737-78-1106 RB, September 1, 2023. The 
FAA has confirmed with Boeing that the Accomplishment Instructions of 
Boeing Special Attention Requirements Bulletin 737-78-1106 RB, 
September 1, 2023, are applicable to the expanded group of airplanes.
    Boeing Special Attention Requirements Bulletin 737-78-1106 RB, 
dated September 1, 2023, identifies ``System Airworthiness Limitation 
NO. 2--Fan Blade Out Conditions,'' and ``System Airworthiness 
Limitation NO. 3--Fan Blade Out Conditions'' as the airworthiness 
limitations that must be incorporated. In addition to those 
limitations, the FAA has determined that ``System Airworthiness 
Limitation NO. 4--Engine Nacelle Maintenance Errors'' must also be 
incorporated as

[[Page 86082]]

specified in paragraph (h) of this proposed AD. System Airworthiness 
Limitation NO. 4 specifically provides the limitation that mandates 
solutions to maintenance errors that must be accomplished prior to 
December 31, 2029, as required by Exemption No. 19212A.

Costs of Compliance

    The FAA estimates that this AD, if adopted as proposed, would 
affect 1,215 airplanes of U.S. registry. The FAA estimates the 
following costs to comply with this proposed AD:

                                                 Estimated Costs
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                                                                                                 Cost on U.S.
             Action                   Labor cost          Parts cost       Cost per product        operators
----------------------------------------------------------------------------------------------------------------
Inspect for affected part         2 work-hours x $85  $0................  $170..............  $206,550.
 numbers or maintenance records    per hour = $170.
 check.
Bridge bracket installation *...  Up 23 work-hours x  Up $63,200........  Up to $65,155.....  Up to $79,163,325
                                   $85 per hour =                                              **.
                                   $1,955.
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* The option to install a serviceable primary exhaust nozzle would cost up to $65,155 per product.
** Not all airplanes will have an affected primary exhaust nozzle so the fleet cost will be significantly lower.

    The FAA has determined that revising the existing maintenance or 
inspection program takes an average of 90 work-hours per operator, 
although the agency recognizes that this number may vary from operator 
to operator. Since operators incorporate maintenance or inspection 
program changes for their affected fleet(s), the FAA has determined 
that a per-operator estimate is more accurate than a per-airplane 
estimate. Therefore, the agency estimates the average total cost per 
operator to be $7,650 (90 work-hours x $85 per work-hour).

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.
    The FAA is 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

    The FAA 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) Would not affect intrastate aviation in Alaska, and
    (3) Would not have a significant economic impact, positive or 
negative, on a substantial number of small entities under the criteria 
of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, 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

0
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]

0
2. The FAA amends Sec.  39.13 by adding the following new airworthiness 
directive:

The Boeing Company: Docket No. FAA-2023-2235; Project Identifier AD-
2023-01009-T.

(a) Comments Due Date

    The FAA must receive comments on this airworthiness directive 
(AD) by January 26, 2024.

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to The Boeing Company Model 737-600, -700, -
700C, -800, -900, and -900ER series airplanes specified in 
paragraphs (c)(1) and (2) of this AD, certificated in any category.
    (1) Airplanes identified in Boeing Special Attention 
Requirements Bulletin 737-78-1106 RB, dated September 1, 2023.
    (2) Airplanes having line numbers 1245, 1614, 1810, 1839, 1885, 
1934, 1979, 1991, 2080, 2157, 2232, 2531, 2822, 3071, 3189, and 
3319.

(d) Subject

    Air Transport Association (ATA) of America Code 78, Exhaust.

(e) Unsafe Condition

    This AD was prompted by two engine fan blade-out (FBO) events 
that resulted in the separation of engine inlet cowl and fan cowl 
parts from the airplane damaging the fuselage, which caused loss of 
pressurization and subsequent emergency descent. The FBO events also 
resulted in cracks in the primary exhaust nozzle, which could result 
in the departure of the primary exhaust nozzle. The FAA is issuing 
this AD to address primary exhaust nozzles that are not 
strengthened, which during an FBO event, could depart the engine, 
potentially damaging a stabilizer or striking the fuselage and 
window. The unsafe condition, if not addressed, could result in loss 
of control of the airplane, or in a rapid decompression and hazard 
to window-seated passengers aft of the wing.

(f) Compliance

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

(g) Required Actions

    Except as specified by paragraph (h) of this AD: At the 
applicable times specified in the ``Compliance'' paragraph of Boeing 
Special Attention Requirements Bulletin 737-78-1106 RB, dated 
September 1, 2023, do all applicable actions identified in, and in 
accordance with, the Accomplishment Instructions of Boeing Special 
Attention Requirements Bulletin 737-78-1106 RB, dated September 1, 
2023.
    Note 1 to paragraph (g): Guidance for accomplishing the actions 
required by this AD can be found in Boeing Special Attention Service 
Bulletin 737-78-1106, dated September 1, 2023, which is referred to 
in Boeing Special Attention Requirements

[[Page 86083]]

Bulletin 737-78-1106 RB, dated September 1, 2023.

(h) Exceptions to Service Information Specifications

    Where Tables 1 and 2 of Boeing Special Attention Requirements 
Bulletin 737-78-1106 RB specify incorporating 737-600/700/700C/800/
900/900ER Airworthiness Limitations (AWLs) document D626A001-9-01 
``System Airworthiness Limitation NO. 2--Fan Blade Out Conditions,'' 
and ``System Airworthiness Limitation NO. 3--Fan Blade Out 
Conditions'' into the operators' maintenance program, this AD 
requires revising the existing maintenance or inspection program, as 
applicable, by incorporating the information specified in Figure 1 
to the introductory text of paragraph (h) of this AD into the 
airworthiness limitations within 90 days after the effective date of 
this AD, or before further flight after accomplishing any of the 
actions specified in paragraphs (h)(1) through (3) of this AD, 
whichever occurs first.

Figure 1 to the Introductory Text of Paragraph (h)--System 
Airworthiness Limitations
[GRAPHIC] [TIFF OMITTED] TP12DE23.000

    (1) The Condition 1, (Option 1) or Condition 3 (Option 1) 
actions specified in Boeing Special Attention Requirements Bulletin 
737-78-1106 RB, dated September 1, 2023.
    (2) The Condition 1, (Option 2) or Condition 3 (Option 2) action 
specified in Boeing Special Attention Requirements Bulletin 737-78-
1106 RB, dated September 1, 2023.
    (3) The determination that the primary exhaust nozzles are not 
affected as specified in Condition 2 or Condition 4 of Boeing 
Special Attention Requirements Bulletin 737-78-1106 RB, dated 
September 1, 2023.

(i) No Alternative Actions

    After the existing maintenance or inspection program has been 
revised as required by paragraph (h) of this AD, no alternative 
actions may be used unless the actions are approved as an 
alternative method of compliance (AMOC) in accordance with the 
procedures specified in paragraph (j) of this AD.

(j) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, AIR-520, Continued Operational Safety Branch, 
FAA, has the authority to approve AMOCs for this AD, if requested 
using the procedures found in 14 CFR 39.19. In accordance with 14 
CFR 39.19, send your request to your principal inspector or 
responsible Flight Standards Office, as appropriate. If sending 
information directly to the manager of the certification office, 
send it to the attention of the person identified in paragraph (k) 
of this AD. Information may be emailed to: [email protected].
    (2) Before using any approved AMOC, notify your appropriate 
principal inspector, or lacking a principal inspector, the manager 
of the responsible Flight Standards Office.
    (3) An AMOC that provides an acceptable level of safety may be 
used for any repair, modification, or alteration required by this AD 
if it is approved by The Boeing Company Organization Designation 
Authorization (ODA) that has been authorized by the Manager, AIR-
520, Continued Operational Safety Branch, FAA, to make those 
findings. To be approved, the repair method, modification deviation, 
or alteration deviation must meet the certification basis of the 
airplane, and the approval must specifically refer to this AD.

(k) Related Information

    For more information about this AD, contact Luis Cortez-Muniz, 
Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 
98198; telephone: 206-231-3958; email: [email protected].

(l) Material Incorporated by Reference

    (1) The Director of the Federal Register approved the 
incorporation by reference (IBR) of the service information listed 
in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.
    (2) You must use this service information as applicable to do 
the actions required by this AD, unless the AD specifies otherwise.
    (i) Boeing Special Attention Requirements Bulletin 737-78-1106 
RB, dated September 1, 2023.
    (ii) [Reserved]
    (3) For service information identified in this AD, contact 
Boeing Commercial Airplanes, Attention: Contractual & Data Services 
(C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-
5600; telephone 562-797-1717; website myboeingfleet.com.
    (4) You may view this service information at the FAA, 
Airworthiness Products Section, Operational Safety Branch, 2200 
South 216th

[[Page 86084]]

St., Des Moines, WA. For information on the availability of this 
material at the FAA, call 206-231-3195.
    (5) You may view this material at the National Archives and 
Records Administration (NARA). For information on the availability 
of this material at NARA, visit www.archives.gov/federal-register/cfr/ibr-locations or email [email protected].

    Issued on December 1, 2023.
Victor Wicklund,
Deputy Director, Compliance & Airworthiness Division, Aircraft 
Certification Service.
[FR Doc. 2023-27101 Filed 12-11-23; 8:45 am]
BILLING CODE 4910-13-P


