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Rule2025-03401

Airworthiness Directives; The Boeing Company Airplanes

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Published

March 4, 2025

Effective

April 8, 2025

Issuing agencies

Transportation DepartmentFederal Aviation Administration

Abstract

The FAA is adopting a new airworthiness directive (AD) for all The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes. 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. In one event, fan cowl parts damaged the fuselage, which caused loss of pressurization and subsequent emergency descent. This AD requires replacing specified inlet cowl aft bulkhead fasteners for certain airplanes; for certain other airplanes, inspecting the inlet cowl aft bulkhead fastener and replacing the fasteners if rivets are found, and, for all airplanes, replacement of the crushable spacers used in the attachment of the inlet cowl to the engine fan case; or as an option, installing a serviceable inlet cowl. This AD also requires revising the existing maintenance or inspection program, as applicable, to incorporate new airworthiness limitations (AWLs). The FAA is issuing this AD to address the unsafe condition on these products.

Full Text

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<title>Federal Register, Volume 90 Issue 41 (Tuesday, March 4, 2025)</title>
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[Federal Register Volume 90, Number 41 (Tuesday, March 4, 2025)]
[Rules and Regulations]
[Pages 11103-11109]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-03401]

[[Page 11103]]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2023-2236; Project Identifier AD-2023-00962-T;
Amendment 39-22959; AD 2025-04-01]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for all
The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER
series airplanes. 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. In one event, fan cowl parts damaged
the fuselage, which caused loss of pressurization and subsequent
emergency descent. This AD requires replacing specified inlet cowl aft
bulkhead fasteners for certain airplanes; for certain other airplanes,
inspecting the inlet cowl aft bulkhead fastener and replacing the
fasteners if rivets are found, and, for all airplanes, replacement of
the crushable spacers used in the attachment of the inlet cowl to the
engine fan case; or as an option, installing a serviceable inlet cowl.
This AD also requires revising the existing maintenance or inspection
program, as applicable, to incorporate new airworthiness limitations
(AWLs). The FAA is issuing this AD to address the unsafe condition on
these products.

DATES: This AD is effective April 8, 2025.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of April 8,
2025.

ADDRESSES:
AD Docket: You may examine the AD docket at <a href="http://regulations.gov">regulations.gov</a> under
Docket No. FAA-2023-2236; 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 final rule, any comments received, and other
information. The address for Docket Operations is U.S. Department of
Transportation, Docket Operations, M-30, West Building Ground Floor,
Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.
Material Incorporated by Reference:
<bullet> For Boeing material 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 <a href="http://myboeingfleet.com">myboeingfleet.com</a>.
<bullet> You may view this material 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 <a href="http://regulations.gov">regulations.gov</a> under
Docket No. FAA-2023-2236.

FOR FURTHER INFORMATION CONTACT: Luis Cortez-Muniz, Aviation Safety
Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; telephone
206-231-3958; email: <a href="/cdn-cgi/l/email-protection#563a233f2578377835392422332c7b3b23383f2c1630373778313920">[email&#160;protected]</a>.

SUPPLEMENTARY INFORMATION:

Background

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14
CFR part 39 by adding an AD that would apply to all The Boeing Company
Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes.
The NPRM published in the Federal Register on December 12, 2023 (88 FR
86084). The NPRM was prompted by two engine FBO events that resulted in
the separation of engine inlet cowl and fan cowl parts from the
airplane. In one event, fan cowl parts damaged the fuselage, which
caused loss of pressurization and subsequent emergency descent. In the
NPRM, the FAA proposed to require replacing specified inlet cowl aft
bulkhead fasteners for certain airplanes; for certain other airplanes,
inspecting the inlet cowl aft bulkhead fastener and replacing the
fasteners if rivets are found, and, for all airplanes, replacement of
the crushable spacers used in the attachment of the inlet cowl to the
engine fan case; or as an option, installing a serviceable inlet cowl.
The NPRM also proposed to require revising the existing maintenance or
inspection program, as applicable, to incorporate new AWLs. The FAA is
issuing this AD to address inlet cowls that are not strengthened, which
could, in the event of an FBO occurrence, depart the airplane
potentially damaging the airframe structure or striking the fuselage
and windows. The unsafe condition, if not addressed, could result in
loss of control of the airplane, and a hazard to window-seated
passengers aft of the wing. In addition, the unsafe condition could
result in significantly increased drag of the airplane, which, during
an extended operations (ETOPS) flight, could lead to fuel starvation
and a forced off-airplane landing.

Other Related Rulemaking

The FAA issued three NPRM ADs related to Exemption No. 19212A,
dated September 7, 2023 (Docket No. FAA-2021-0681) (Exemption No.
19212A), which requires Boeing to develop modifications to the inlet
cowl, fan cowl, and exhaust nozzle for operators to incorporate by July
31, 2028. Exemption No. 19212A further requires Boeing to provide
solutions to address maintenance errors. Exemption No. 19212A also
requires Boeing to develop airworthiness limitations for the
modifications and solutions to address maintenance errors.
The NPRM for this AD, Docket No. FAA-2023-2236, refers to Boeing
Special Attention Requirements Bulletin 737-71-1938, dated July 27,
2023, as the appropriate source of service information for
accomplishing the proposed modifications to the inlet cowl.
The NPRM for Docket No. FAA-2023-2234 (88 FR 86069, December 12,
2023) refers to Boeing Special Attention Requirements Bulletin 737-71-
1937, dated July 27, 2023, as the appropriate source of service
information for accomplishing the proposed modifications to the fan
cowl.
The NPRM for Docket No. FAA-2023-2235 (88 FR 86080, December 12,
2023) refers to Boeing Special Attention Requirements Bulletin 737-78-
1106, dated September 1, 2023, as the appropriate source of service
information for accomplishing the proposed modifications to the exhaust
nozzle.
All three NPRMs also proposed to require revising the existing
maintenance or inspection program, as applicable, to incorporate new
airworthiness limitations (System Airworthiness Limitations No. 2, No.
3, and No. 4).

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from Air Line Pilots Association,
International (ALPA) who supported the NPRM without change.
The FAA received additional comments from 13 commenters, including
AIRDO, All Nippon Airways, American Airlines, Aviation Partners Boeing,
Boeing, Delta Air Lines, Qantas, SIA Engineering, Southwest Airlines,
Sun Country Airlines, United Airlines, Virgin Australia Airlines, and
an individual commenter. The following presents the comments received
on the NPRM and the FAA's response to each comment.

[[Page 11104]]

Request for Clarification of the Applicability

SIA Engineering requested that the FAA clarify the applicability of
the proposed AD to match the part number applicability included in the
effectivity paragraph of Collins Aerospace Service Bulletin 737NG-71-
007. The commenter stated that the NPRM applies to all Boeing Model
737-600, -700, -700C, -800, -900, and -900ER series airplanes, whereas
the effectivity paragraph for Collins Aerospace Service Bulletin 737NG-
71-007, Revision 0, dated July 28, 2023, references the affected
components (i.e., part numbers 314-2100-2, 314-2100-3, and 314-2100-4
with serial numbers before 14220001). Sun Country Airlines also stated
that the proposed applicability specifies all airplanes, but the
service information identifies affected parts.
The FAA agrees to clarify the applicability. The applicability for
this AD affects all Boeing Model 737-600, -700, -700C, -800, -900, and
-900ER series airplanes. The FAA confirmed with Boeing that all Boeing
Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes
with inlet cowl part numbers (P/Ns) 314-2100-2, 314-2100-3, and 314-
2100-4, regardless of serial number, are in the effectivity of Boeing
Special Attention Requirements Bulletin 737-71-1938 RB, which lists
airplane line numbers, and Collins Aerospace Service Bulletin 737NG-71-
007, which refers to the inlet cowl part numbers having serial numbers
before 14220001. All applicable airplanes were delivered with inlet
cowl P/Ns 314-2100-2, 314-2100-3, and 314-2100-4, which must be
modified to address the unsafe condition. The effectivity of Boeing
Special Attention Requirements Bulletin 737-71-1938 RB, Revision 1,
dated June 27, 2024, lists line numbers, which is equivalent to all
airplanes. The effectivity of Collins Aerospace Service Bulletin 737NG-
71-007, dated July 28, 2023, refers to affected inlet cowls (P/Ns 314-
2100-2, 314-2100-3, and 314-2100-4) and specifies serial numbers prior
to serial number 14220001, which is equivalent to all affected inlet
cowls. Starting at serial number 14220001, the corresponding part
number will be 314-2100-5, which is the new part that is equivalent to
the inlet cowls modified as specified in Collins Aerospace Service
Bulletin 737NG-71-007, dated July 28, 2023. The FAA has not changed
this AD as a result of this comment.

Request for Clarifying Part Interchangeability

Sun Country Airlines stated there is a possibility of an aircraft
becoming out of compliance due to replacement of a modified inlet cowl
with an unmodified inlet cowl. Sun Country Airlines stated that other
rulemaking that has affected components has had wording identifying or
limiting pre- and post-modification installation/interchangeability.
The FAA infers Sun Country Airlines is requesting that the FAA add a
note to the proposed AD to specify a modified inlet cowl cannot be
replaced with an unmodified inlet cowl.
The FAA agrees to clarify. 14 CFR 39.7 specifies that once an AD is
issued, no person may operate a product to which the AD applies except
in accordance with the requirements of that AD. Further, 14 CFR 39.9
imposes a continuing obligation to maintain compliance with an AD by
establishing a separate violation for each time an aircraft is operated
that fails to meet AD requirements. Thus, operators have an ongoing
obligation to ensure that the AD-mandated configuration is maintained.
Therefore, adding the part restriction note would not be necessary
since all Boeing Model 737-600, -700, -700C, -800, -900, and -900ER
series airplanes are required to accomplish Boeing Special Attention
Requirements Bulletin 737-71-1938 RB. The FAA has not changed this AD
in this regard.

Request To Refer to Later Revisions of the Service Information

Southwest Airlines and American Airlines requested that the FAA
change paragraphs (g) and (h) of the proposed AD to reference Boeing
Special Attention Requirements Bulletin 737-71-1938 RB, Revision 1,
which is pending publication. Southwest Airlines asked that the FAA not
publish the AD until the release of Revision 1 and allow credit for
previous accomplishment of the original issue of the requirements
bulletin.
American Airlines also requested that the FAA allow the use of
later FAA-approved revisions of Boeing Special Attention Requirements
Bulletin 737-71-1938 RB. American Airlines stated this is no different
than when the FAA incorporates a European Union Aviation Safety Agency
(EASA) AD into an FAA AD by reference, and the EASA AD ``Ref.
Publications'' section states, ``The use of later approved revisions of
the above-mentioned document is acceptable for compliance with the
requirements of this AD.'' American Airlines concluded that this change
will prevent the need for immediate, if not on-going requests for
alternative methods of compliance (AMOCs) upon the release of the
revised service bulletins.
The FAA has reviewed Boeing Special Attention Requirements Bulletin
737-71-1938 RB, Revision 1, dated June 27, 2024. This revision adds
``System Airworthiness Limitation NO. 4--Engine Nacelle Maintenance
Errors'' to the actions to incorporate airworthiness limitations. The
AWLs are now incorporated into Revision 1 of Boeing Special Attention
Requirements Bulletin 737-71-1938 RB so this information can now be
required via Boeing Special Attention Requirements Bulletin 737-71-1938
RB, Revision 1, dated June 27, 2024, instead of as an exception to the
service information. In addition to incorporating the AWL information
that was specified in figure 1 to the introductory text of paragraph
(h) of the proposed AD, the only other changes to the ``Compliance''
paragraph and Accomplishment Instructions of Boeing Special Attention
Requirements Bulletin 737-71-1938 RB, Revision 1, dated June 27, 2024,
were to reference the NPRM, clarify Note 1 that describes the
``Enhanced Required for Compliance'' document, and to add Note 10 to
allow alternative fasteners. None of these changes substantively affect
the required actions for operators but instead are clarifying.
Therefore, the FAA has revised this AD to refer to Boeing Special
Attention Requirements Bulletin 737-71-1938 RB, Revision 1, dated June
27, 2024, and added paragraph (j) of this AD to provide credit for
previous work performed prior to the effective date of this AD.
Regarding the American Airlines request to include later approved
revisions, the FAA cannot allow later approved revisions in the AD
because referring to documents that do not exist at the time the AD is
published violates Office of the Federal Register (OFR) regulations
regarding approval of materials ``incorporated by reference'' in rules.
These OFR regulations require that either the service document be
submitted for approval by the OFR as ``referenced'' material, in which
case it may be simply called out in the text of an AD, or the service
document contents be published as part of the actual AD language. An AD
may reference only the specific service document that was submitted and
approved by the OFR for ``incorporation by reference.'' In order for
operators to use later revisions of the referenced document (issued
after the publication of the AD), either the FAA must revise the AD to
reference the specific later revisions, or operators must request the
approval of their use as an AMOC (under the provisions of paragraph (k)
of this AD).

[[Page 11105]]

Request for AWL Compliance Time Extension

AIRDO, All Nippon Airways, American Airlines, Delta Air Lines,
Qantas, Sun Country Airlines, United Airlines, and Virgin Australia
Airlines requested the compliance time for revising the existing
maintenance or inspection program be extended from before further
flight as specified in the proposed AD to a longer compliance time.
Compliance time requests varied from 30 days to 12 months. Some
commenters stated that the ``before further flight'' requirement should
be removed altogether. Several commenters noted that voluntary
incorporation of the modification is occurring but incorporating the
AWLs before further flight after modification was not possible since
the AWLs were not published at the same time as the modification
bulletins. Several commenters expressed concern that this will result
in non-compliance with the AD upon its effective date. Qantas requested
that for airplanes on which the modification specified in Boeing
Special Attention Requirements Bulletin 737-71-1938 RB has already been
done, the FAA allow figure 1 to the introductory text of paragraph (h)
of the proposed AD to be incorporated within 30 days after the
effective date of the AD instead of before further flight after
accomplishing actions specified in Boeing Special Attention
Requirements Bulletin 737-71-1938 RB. Virgin Australian Airlines also
requested credit if modification of the inlet cowl was accomplished
prior to the AD's effective date. Sun Country Airlines also expressed
concern that the AWL revision and updated requirements have not been
approved or released via normal distribution channels.
The FAA disagrees with changing the compliance time but
acknowledges the concern regarding the compliance time for airplanes on
which the modification was done prior to adoption of this AD and
availability of the updated AWL. However, the requirement to
incorporate the AWLs before further flight is in accordance with
Exemption No. 19212A, Docket No. FAA-2021-0681 and is part of the
change to type design. The FAA provided a time-limited exemption (TLE)
to Boeing, Exemption No. 19212A. The TLE includes a limitation to
require the AWLs to be incorporated as part of the type design for each
of the modifications which include engine inlet, fan cowl and fan cowl
support beam, and exhaust nozzle. As the modification plus the AWL is
required to maintain a compliant design, this AD will maintain the
``before further flight'' requirement.
The FAA also notes that paragraph (f) of this AD states to
accomplish the required actions within the compliance times specified,
``unless already done.'' Therefore, if operators have accomplished the
modification and incorporation of the AWLs required for compliance with
this AD before the effective date of this AD, no further action is
necessary.

Request the Removal of AWL Incorporation

American Airlines, Delta Air Lines, Sun Country Airlines, Southwest
Airlines, Qantas, and United Airlines requested removing the
requirement to incorporate some or all of the AWLs specified in the
proposed AD (System Airworthiness Limitations No. 2, No. 3, and No. 4).
The commenters pointed out that paragraph (h) of the proposed AD
specifies incorporating certain AWLs included in Boeing 737-600/700/
700C/800/900/900ER Airworthiness Limitations (AWLs) Document D626A001-
9-01. The commenters noted that the current published Boeing 737-600/
700/700C/800/900/900ER Airworthiness Limitations (AWLs) Document
D626A001-9-01 does not include the AWLs specified in figure 1 to the
introductory text of paragraph (h) of the proposed AD, which are vague
and do not provide a definitive action to address the unsafe condition
identified in the proposed AD. Qantas stated that operators do not have
instructions to modify the engine exhaust nozzles in Boeing Special
Attention Requirements Bulletin 737-71-1938 RB, July 27, 2023, and
suggested that System Airworthiness Limitation No. 3 be removed from
the proposed AD (the NPRM for Docket No. FAA-2023-2234) and only be
located in NPRM Docket No. FAA-2023-2235 where it is more suited.
Sun Country Airlines stated System Airworthiness Limitation No. 4
does not appear related to the events that prompted the NPRM and is not
related to the intent of this rulemaking. Southwest stated that
incorporating System Airworthiness Limitation No. 4 places
responsibility on the operator, rather than the manufacturer, to be
compliant and produce solutions. Southwest added that Boeing has a
responsibility to define ``potential maintenance errors'' and to
provide specific modification or inspection procedures to mitigate
those errors. The commenters also raised concerns that an immediate
change to the maintenance program would not provide additional safety
measures. The commenters expressed further concern that the new
proposed requirements may result in airplanes being out of revenue
service while waiting on an operator's Certificate Management Office
(CMO) to process the maintenance program change. Delta recommended that
the FAA transfer the AWL requirements into a separate AD.
The FAA disagrees with removing some or all of the AWLs specified
in this AD. The FAA requirement to incorporate the AWLs before further
flight is in accordance with the modifications required by Exemption
No. 19212A to address the unsafe condition. Furthermore, the TLE
includes a limitation to require that the AWLs be incorporated as part
of the type design for modifications to the engine inlet, fan cowl and
fan cowl support beam, and exhaust nozzle. Therefore, once one of the
modification bulletins (Boeing Special Attention Requirements Bulletins
737-71-1937 RB, 737-71-1938 RB, and 737-78-1106 RB) is accomplished,
all the AWLs specified in this AD need to be incorporated into the
operators' maintenance program so as the operator can maintain a
compliant design and address the unsafe condition. System Airworthiness
Limitations No. 2, No. 3, and No. 4 were created to address the TLE
requirements and the unsafe condition.
A new version of the AWLs has been released, Boeing 737-600/700/
700C/800/900/900ER Airworthiness Limitations (AWLs) Document D626A001-
9-01, dated January 2024, that includes the AWLs identified in figure 1
to the introductory text of paragraph (h) of the proposed AD. Boeing
Special Attention Requirements Bulletin 737-71-1938 RB, Revision 1,
dated June 27, 2024, includes procedures to incorporate those new AWLs.
Therefore, the FAA has determined that incorporating the new AWLs must
be done as part of the requirements of this AD and not in a separate
AD.

Request To Change AWL Compliance Time

Southwest Airlines suggested either a service data due date of
December 31, 2024 to align with the time-limited exemption, Exemption
No. 19212A, be added to the proposed AD or that the FAA remove the AWL
requirements from the proposed AD. Southwest Airlines stated System
Airworthiness Limitations No. 2, No. 3, and No. 4 do not provide a
defined date for Boeing to release all service data to operators.
Therefore, without a defined date for Boeing to release all service
data, there

[[Page 11106]]

is concern that operators may not be given sufficient time to perform
the required modifications prior to the AD's completion due date.
The FAA disagrees with the commenter's request. As previously
mentioned, a new AWL revision has been released that includes the
System Airworthiness Limitations No. 2 and No. 3, and No. 4. The
service information for System Airworthiness Limitations. No. 2 and No.
3 has been released, i.e., Boeing Special Attention Requirements
Bulletin 737-71-1938, dated July 27, 2023, and Revision 1, dated June
27, 2024; Boeing Special Attention Requirements Bulletin 737-71-1937,
dated July 27, 2023, and Revision 1, dated June 27, 2024; and Boeing
Special Attention Requirements Bulletin 737-78-1106, dated September 1,
2023, and Revision 1, dated May 23, 2024. Although service information
to address System Airworthiness Limitation No. 4 has not yet been
released, the FAA has coordinated with Boeing to better understand the
requirements of System Airworthiness Limitation No. 4, which requires
the incorporation of solutions to address potential engine nacelle
maintenance errors into operators' maintenance programs. The solutions
are intended to prevent the unlatching of the fan cowl and fan cowl
integrated drive generator (IDG) door in flight. The solutions will
consist of a re-designed fan cowl latch and keeper and application of
high visibility paint on the interior of the IDG door. The FAA has
added an exception to paragraph (h)(2) of this AD to clarify solutions
as required in System Airworthiness Limitation No.4. Operators have
until December 31, 2029, to incorporate solutions to address potential
maintenance errors as specified in System Airworthiness Limitation No.4
and clarified in this AD.

Request for Clarification Regarding AWL Requirement

Delta Air Lines, All Nippon Airways, United Airlines, Qantas, and
American Airlines asked for clarification on what would be required to
meet System Airworthiness Limitations No. 2, No. 3, and No. 4. The
commenters stated adequate instructions are not included in the AWLs.
Therefore, additional details are needed to clarify these requirements
and provide a clear path to comply with the AWLs specified in figure 1
to the introductory text of paragraph (h) of the proposed AD.
Furthermore, certain operators do not believe this meets 14 CFR 43.16,
and System Airworthiness Limitation No.4 is an unexpected demand.
The FAA agrees to clarify. Accomplishing the modification specified
in Boeing Special Attention Requirements Bulletins 737-71-1938 RB, 737-
71-1937 RB, and 737-78-1106 RB satisfies the requirements of System
Airworthiness Limitations No. 2 and No. 3. This also satisfies the
requirement of 14 CFR 43.16 to perform inspections or maintenance in
accordance with the AWLs.
As denoted in paragraph 4., ``Approval'' of Boeing Special
Attention Requirements Bulletin 737-71-1938, Revision 1, dated June 27,
2024, the accomplishment of that requirements bulletin meets the
requirements of item (1) of Boeing 737-600/700/700C/800/900/900ER
Airworthiness Limitations (AWLs) Document D626A001-9-01 ``SYSTEM
AIRWORTHINESS LIMITATION NO. 2.''
As denoted in paragraph 4., ``Approval'' of Boeing Special
Attention Requirements Bulletin 737-71-1937, Revision 1, dated June 27,
2024, the accomplishment of that requirements bulletin meets the
requirements of items (2) and (3) of Boeing 737-600/700/700C/800/900/
900ER Airworthiness Limitations (AWLs) Document D626A001-9-01 ``SYSTEM
AIRWORTHINESS LIMITATION NO. 2.''
As denoted in paragraph 4., ``Approval'' of Boeing Special
Attention Requirements Bulletin 737-78-1106, Revision 1, dated May 23,
2024, the accomplishment of that requirements bulletin meets the
requirements of Boeing 737-600/700/700C/800/900/900ER Airworthiness
Limitations (AWLs) Document D626A001-9-01 ``SYSTEM AIRWORTHINESS
LIMITATION NO. 3--FAN BLADE OUT CONDITIONS.''
As previously stated, the FAA coordinated with Boeing to determine
potential maintenance errors that require solutions in accordance with
System Airworthiness Limitation No. 4. To comply with this AD and the
System Airworthiness Limitation No. 4, solutions will consist of a re-
designed fan cowl latch and keeper and application of high visibility
paint on the interior of the IDG door. If any specific service
information is provided or further solutions are incorporated to
address potential maintenance errors, the FAA may consider further
rulemaking.

Request for Change to Exception (System Airworthiness Limitation No. 4)

Boeing requested appending the following statement to the end of
System Airworthiness Limitation No. 4.: ``Boeing will release all
service data to enable full compliance for the CFM56-7B nacelle for
addressing potential maintenance errors prior to that date.'' Boeing
stated that the statement would correspond to the statements included
in AWL No. 2 and 3.
The FAA agrees to clarify. As previously mentioned, the recently
released Boeing AWL document includes System Airworthiness Limitation
No. 4. The new AWL includes the text as requested by Boeing. Therefore,
no change to this AD is necessary.

Request To Add Additional Service Information

Sun Country Airlines noted that the proposed AD only refers to
Boeing Special Attention Requirements Bulletin 737-71-1938 RB, dated
July 27, 2023, and requested that the FAA list additional service
information as documentation to be used for compliance with the
proposed rule. The commenter noted that other service information
contains critical details of the inlet attach ring fastener replacement
work.
The FAA partially agrees. The FAA agrees that several actions in
Collins Aerospace Service Bulletin 737NG-71-007, Revision 0, dated July
28, 2023, are required for compliance as specified by Boeing Special
Attention Requirements Bulletin 737-71-1938 RB, Revision 1, dated June
27, 2024, which is required by paragraph (g) of this AD. The FAA also
acknowledges that certain other service information might be related to
the required actions. However, the FAA only identifies service
information that is directly required for compliance by this AD. The
FAA has not changed this AD in this regard.

Request To Add an Exception for Equivalent Consumables

United Airlines requested the FAA add an exception to allow
equivalent consumables substitutes for sealant, primer, etc., to be
used during the accomplishment of the proposed AD. United Airlines
noted that table 2.C in Collins Aerospace Service Bulletin 737NG-71-007
allows an equivalent substitute to certain consumables to be used but
these substitutes are not allowable as part of the ``Required for
Compliance'' (RC) steps. Instead, United Airlines stated Collins
Aerospace Service Bulletin 737NG-71-007 calls out specific consumable
products in the RC steps; this violates standard practice where
typically a material specification is referenced instead of a specific
manufacturer product.

[[Page 11107]]

The FAA agrees with the request. By allowing equivalent material
substitutes, this AD still adequately addresses the identified unsafe
condition. Therefore, the FAA has added paragraph (h)(3) of this AD to
allow equivalent material substitutes for the use of Bonderite M-CR
1200S Aero, 10P4-2NF primer, EC-117S converter, TR19 thinner, or T20
thinner.

Request To Change a Certain Fastener Requirement

An individual advised the FAA of the need for dimensional
inspection and conformance requirements of the threaded fasteners and
recommended using AS8879 Category 2 fasteners instead of Category 1
fasteners.
The FAA clarifies that Boeing Special Attention Requirements
Bulletin 737-71-1938 RB, Revision 1, dated June 27, 2024, specifies the
approved part numbers of the fasteners for this modification. The
subject inlet configuration was found to meet the pertinent structural
regulations with the existing fastener thread specifications. The FAA
has not changed this AD as a result of this comment.

Effect of Winglets on Accomplishment of the Proposed Actions

Aviation Partners Boeing stated that the installation of winglets
per supplemental type certificate (STC) ST00830SE on applicable Boeing
models subject to the proposed rule does not affect compliance with the
mandated actions in the proposed AD.
The FAA agrees with the commenter that STC ST00830SE does not
affect the ability to accomplish the actions required by this AD. The
FAA has not changed this AD in this regard.

Conclusion

The FAA reviewed the relevant data, considered any comments
received, and determined that air safety requires adopting this AD as
proposed. Accordingly, the FAA is issuing this AD to address the unsafe
condition on these products. Except for minor editorial changes, and
any other changes described previously, this AD is adopted as proposed
in the NPRM. None of the changes will increase the economic burden on
any operator.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Boeing Special Attention Requirements Bulletin
737-71-1938 RB, Revision 1, dated June 27, 2024. This material
specifies procedures to accomplish replacement of specified inlet cowl
aft bulkhead fasteners for certain airplanes; for certain other
airplanes, an inlet cowl aft bulkhead fastener inspection and fastener
replacement of the inlet cowl aft bulkhead fasteners if rivets are
found, and, for all airplanes, replacement of the crushable spacers
used in the attachment of the inlet cowl to the engine fan case for
engine 1 and engine 2; or as an option, installation of a serviceable
inlet cowl with new crushable spacers. This material also specifies
procedures to incorporate Boeing 737-600/700/700C/800/900/900ER
Airworthiness Limitations (AWLs) Document D626A001-9-01 ``System
Airworthiness Limitation No. 2--Fan Blade Out Conditions'', ``System
Airworthiness Limitation No. 3--Fan Blade Out Conditions,'' and
``System Airworthiness Limitation No. 4--Engine Nacelle Maintenance
Errors'' into the operator's maintenance or inspection program.
This material is reasonably available because the interested
parties have access to it through their normal course of business or by
the means identified in ADDRESSES.

Costs of Compliance

The FAA estimates that this AD affects 1,979 airplanes of U.S.
registry. The FAA estimates the following costs to comply with this AD:

Estimated Costs
----------------------------------------------------------------------------------------------------------------
Parts
Action * Labor cost cost Cost per product Cost on U.S. operators
----------------------------------------------------------------------------------------------------------------
Inspection and fastener Up to 98 work- $922 Up to $9,252.......... Up to $18,309,708.
replacement (for Config 1 hours x $85 per
airplanes)/Fastener hour = $8,330.
replacement (for Config 2
airplanes).
Crushable spacer replacement.. 16 work-hours x 14,878 $16,238............... $32,135,002.
$85 per hour =
$1,360.
----------------------------------------------------------------------------------------------------------------
* The option to install a serviceable inlet cowl would cost up to $25,490 per product.

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

This AD will not have federalism implications under Executive Order
13132. This AD 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.
For the reasons discussed above, I certify that this AD:
(1) Is not a ``significant regulatory action'' under Executive
Order 12866,
(2) Will not affect intrastate aviation in Alaska, 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.

[[Page 11108]]

List of Subjects in 14 CFR Part 39

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

The Amendment

Accordingly, under the authority delegated to me by the
Administrator, the FAA amends 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:

2025-04-01 The Boeing Company: Amendment 39-22959; Docket No. FAA-
2023-2236; Project Identifier AD-2023-00962-T.

(a) Effective Date

This airworthiness directive (AD) is effective April 8, 2025.

(b) Affected ADs

None.

This AD applies to all The Boeing Company Model 737-600, -700, -
700C, -800, -900, and -900ER series airplanes, certificated in any
category.

(d) Subject

Air Transport Association (ATA) of America Code 71, Powerplant.

(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. In one event, fan cowl parts damaged the
fuselage, which caused loss of pressurization and subsequent
emergency descent. The FAA is issuing this AD to address inlet cowls
that are not strengthened, which, in the event of an FBO occurrence,
could depart the airplane potentially damaging the airframe
structure, or the inlet cowl could strike the fuselage and window.
The unsafe condition, if not addressed, could result in loss of
control of the airplane and hazard to window-seated passengers aft
of the wing. In addition, the unsafe condition could result in
significantly increased drag of the airplane, which during an
extended operations (ETOPS) flight, could lead to fuel starvation
and a forced off-airplane landing.

(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 737-71-1938 RB, Revision 1,
dated June 27, 2024, do all applicable actions identified in, and in
accordance with, the Accomplishment Instructions of Boeing Special
Attention Requirements Bulletin 737-71-1938 RB, Revision 1, dated
June 27, 2024.
Note 1 to paragraph (g): Guidance for accomplishing the actions
required by this AD can be found in Boeing Special Attention Service
Bulletin 737-71-1938, Revision 1, dated June 27, 2024, which is
referred to in Boeing Special Attention Requirements Bulletin 737-
71-1938 RB, Revision 1, dated June 27, 2024.

(h) Exceptions to Service Information Specifications

(1) Where the Compliance Time columns of the tables in the
``Compliance'' paragraph of Boeing Special Attention Requirements
Bulletin 737-71-1938 RB, Revision 1, dated June 27, 2024, refer to
the original issue date of Requirements Bulletin 737-71-1938 RB,
this AD requires using the effective date of this AD.
(2) Where System Airworthiness Limitation No. 4, as identified
in Boeing Special Attention Requirements Bulletin 737-71-1938 RB,
Revision 1, dated June 27, 2024, requires incorporation of solutions
to address potential engine nacelle maintenance errors, solutions
consist of a re-designed fan cowl latch and keeper and application
of high visibility paint on the interior of the integrated drive
generator (IDG) door.
(3) Where Collins Aerospace Service Bulletin 737NG-71-007
referenced in Boeing Special Attention Requirements Bulletin 737-71-
1938 RB, Revision 1, dated June 27, 2024, specifies use of Bonderite
M-CR 1200S Aero, 10P4-2NF primer, EC-117S converter, TR19 thinner,
or T20 thinner, this AD also allows for equivalent material
substitutes as specified in paragraph 2.C., ``Material Necessary for
Each Inlet Assembly,'' of Collins Aerospace Service Bulletin 737NG-
71-007 referenced in Boeing Special Attention Requirements Bulletin
737-71-1938 RB, Revision 1, dated June 27, 2024.

(i) No Alternative Actions

After the existing maintenance or inspection program has been
revised as required by paragraph (g) 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 (k) of this AD.

(j) Credit for Previous Actions

This paragraph provides credit for the actions specified in
paragraph (g) of this AD, if those actions were performed before the
effective date of this AD using Boeing Special Attention
Requirements Bulletin 737-71-1938 RB, dated July 27, 2023, provided
where Tables 1 through 4 of Boeing Special Attention Requirements
Bulletin 737-71-1938 RB, dated June 27, 2024, 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,
the information specified in figure 1 to paragraph (j) of this AD
has been incorporated into the airworthiness limitations.

Figure 1 to Paragraph (j)--System Airworthiness Limitations

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

-------------------------------------------------------------------------
SYSTEM AIRWORTHINESS LIMITATION No. 2
FAN BLADE OUT CONDITIONS
All aircraft must install the following modifications: (1) engines
inlets with new spacer design and increased fastner capability (2) fan
cowls with new radial restraint fitting hooks, new radial restraint
clips, and an external doubler at the starter vent (3) fan cowl support
beam fastner changes (except for 737-900ER aircraft, because the fan
cowl support beam fastner changes are already incorporated). All
aircraft that have not incorporated these modifications cannot operate
past July 31, 2028, unless upgraded to a new hardware that is fully
compliant to to Sec. Sec. 25.901(c) and Appendix K25.1.1 to Part 25.
Boeing will release all service data to allow retrofit of hardware
updates to the CFM56-7B nacelle prior to that date.

SYSTEM AIRWORTHINESS LIMITATION No. 3
FAN BLADE OUT CONDITIONS
All aircraft delivered without the Performance Improvement Package (PIP)
must install engine exhaust nozzle structural stiffening elements. All
aircraft that have not incorporated these modifications cannot operate
past July 31, 2028 unless upgraded to new hardware that is fully
compliant to Sec. Sec. 25.901(c) and Appendix K25.1.1 to Part 25.
Boeing will release all service data to allow retrofit of hardware
updates to the CFM56-7B nacelle prior to that date.

[[Page 11109]]

SYSTEM AIRWORTHINESS LIMITATION No. 4
ENGINE NACELLE MAINTENANCE ERRORS
All aircraft must incorporate solutions to address potential maintenance
errors, e.g., the failure to completely latch the fan cowl or the can
cowl integrated drive generator (IDG) door. All aircraft that have not
incorporated changes to become fully compliance with Sec. Sec.
25.901(c) and Appendix K25.1.1 to Part 25 cannot be operated past
December 31, 2029.
------------------------------------------------------------------------

(k) 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
(l)(1) of this AD. Information may be emailed to: <a href="/cdn-cgi/l/email-protection#03424e4c40436562622d646c75">[email&#160;protected]</a>.
(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.

(l) Related Information

(1) 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: <a href="/cdn-cgi/l/email-protection#3b574e5248155a155854494f5e4116564e5552417b5d5a5a155c544d">[email&#160;protected]</a>.
(2) For Collins material identified in this AD that is not
incorporated by reference, contact Collins Aerospace, 15701 West
95th Street, Lenexa, KS 66219; email <a href="/cdn-cgi/l/email-protection#e6afb5b693848a8f8587928f898895a685898a8a8f8895c885898b">[email&#160;protected]</a>;
website <a href="http://tpi.beaerospace.com/Authentication">tpi.beaerospace.com/Authentication</a>.
(3) Boeing material identified in this AD that is not
incorporated by reference is available at the address specified in
paragraph (m)(3) this AD.

(m) Material Incorporated by Reference

(1) The Director of the Federal Register approved the
incorporation by reference (IBR) of the material listed in this
paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.
(2) You must use this material as applicable to do the actions
required by this AD, unless the AD specifies otherwise.
(i) Boeing Special Attention Requirements Bulletin 737-71-1938
RB, Revision 1, dated June 27, 2024.
(ii) [Reserved]
(3) For Boeing material 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 <a href="http://myboeingfleet.com">myboeingfleet.com</a>.
(4) You may view this material 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.
(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 <a href="http://www.archives.gov/federal-register/cfr/ibr-locations">www.archives.gov/federal-register/cfr/ibr-locations</a> or email <a href="/cdn-cgi/l/email-protection#284e5a0641465b584d4b5c4147466846495a49064f475e">[email&#160;protected]</a>.

Issued on February 25, 2025.
Suzanne Masterson,
Deputy Director, Integrated Certificate Management Division, Aircraft
Certification Service.
[FR Doc. 2025-03401 Filed 3-3-25; 8:45 am]
BILLING CODE 4910-13-P

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