[Federal Register Volume 90, Number 41 (Tuesday, March 4, 2025)]
[Rules and Regulations]
[Pages 11109-11116]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2025-03395]
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2023-2234; Project Identifier AD-2023-00963-T;
Amendment 39-22960; AD 2025-04-02]
RIN 2120-AA64
Airworthiness Directives; The Boeing Company Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final rule.
-----------------------------------------------------------------------
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 the fasteners on the fan
cowl support beam hinge fittings for certain airplanes and, for all
airplanes, requires modifying the radial restraint assembly and
installing an external doubler at the starter vent, or as an option,
installing a serviceable fan cowl. This AD also requires revising the
existing maintenance or inspection program, as applicable, to
incorporate new airworthiness limitations. 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 regulations.gov under
Docket No. FAA-2023-2234; 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:
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 myboeingfleet.com.
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 regulations.gov under
Docket No. FAA-2023-2234.
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:
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
86069). 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
[[Page 11110]]
FAA proposed to require replacing the fasteners on the fan cowl support
beam hinge fittings for certain airplanes and, for all airplanes,
proposed to require modifying the radial restraint assembly and
installing an external doubler at the starter vent, or as an option,
installing a serviceable fan cowl. In the NPRM, the FAA also proposed
to require revising the existing maintenance or inspection program, as
applicable, to incorporate new airworthiness limitations. The FAA is
issuing this AD to address fan cowls that are not strengthened, which
could, in the event of an FBO occurrence, depart the nacelle
potentially damaging a stabilizer, or the fan cowl could strike 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.
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-2023-2234, 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-2023-2236 (88 FR 86084, December 12,
2023) 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-2023-2235 (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 11 commenters, including
AIRDO, All Nippon Airways, American Airlines, Aviation Partners Boeing,
Boeing, Delta Air Lines, Qantas, Southwest Airlines, Sun Country
Airlines, United Airlines, and Virgin Australia Airlines. The following
presents the comments received on the NPRM and the FAA's response to
each comment.
Request To Clarify Part Interchangeability
Sun Country Airlines stated there is a possibility of an aircraft
becoming out of compliance due to replacement of a modified fan cowl
with an unmodified fan 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 fan cowl cannot be
replaced with an unmodified fan 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 737-71-1937 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 737-71-1937 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 737-71-1937 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
737-71-1937 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 737-71-1937 RB so this information can now be
required via Boeing Special Attention Requirements Bulletin 737-71-1937
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 737-71-1937 RB, Revision 1, dated June 27, 2024,
were to reference the NPRM, clarify Note 1 that describes the
``Enhanced Required for Compliance'' document, add Note 8 to allow
alternative fasteners and add an optional concurrent service bulletin.
None of these changes substantively affect the required actions on
operators but instead are clarifying. Therefore, the FAA has revised
this AD to refer to Boeing Special Attention Requirements Bulletin 737-
71-1937 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
[[Page 11111]]
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).
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 737-71-1937 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 737-71-1937 RB. Virgin Australian Airlines
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 the adoption of this AD and
the 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 some or all of
the AWLs specified in the proposed AD (System AWLs 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 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, and added that the current
AWLs 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 737-71-1937 RB, July
27, 2023, and suggested that System Airworthiness Limitation No. 3 be
removed from the proposed AD and only be located in the NPRM for Docket
No. FAA-2023-2235 where it is more suited.
Sun Country Airlines stated System Airworthiness Limitation No. 4
does not appear to be 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. Some commenters also raised concerns that an immediate
change to the maintenance program would not provide additional safety
measures. American Airlines 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 modification 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 737-71-1937 RB, Revision 1,
dated June 27, 2024, includes
[[Page 11112]]
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 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)(3) of this AD to clarify solutions
as required in AWL No.4. Operators have until December 31, 2029, to
incorporate solutions to address potential maintenance errors as
specified in AWL No.4. and clarified in this AD.
Request for Clarification Regarding AWL Requirement
Delta Air Lines, 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 737-71-1937, 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 737-71-1938, 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 737-78-1106, 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 new Boeing AWL document includes System AWL 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 737-71-1937 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 fan cowl work.
The FAA partially agrees. The FAA agrees that several actions in
the Collins Aerospace Service Bulletin 737NG-71-008 are required for
compliance as specified by Boeing Special Attention Requirements
Bulletin 737-71-1937 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
[[Page 11113]]
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-71-008 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-71-008 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.
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)(4) 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 Use Alternative Documents for Primer Application
United Airlines requested that a primer application step in Collins
Service Bulletin 737NG-71-008 (which is referenced in Boeing Special
Attention Requirements Bulletin 737-71-1937 RB) be revised to reference
commonly used manuals such as standard overhaul practices manual (SOPM)
20-41-02 or other equivalent documents. United Airlines stated that
Collins Service Bulletin currently states to ``apply primer over the
repair area per Boeing document D6-1816''. United Airlines noted that
document D6-1816 document is used by Boeing during production and is
not accessible to technicians.
The FAA agrees with the commenter's request. The SOPM maintains the
intended configuration and is a manual readily accessible to
technicians. The FAA has added paragraph (h)(5) of this AD to allow
using the SOPM for primer application.
Request for Exception to Certain Work Step
United Airlines requested provisions be added in the final rule to
allow installation of the external doubler and new radial restraint to
be performed concurrently as they are independent installations and do
not adversely affect the intent of the modification. The commenter
stated that Boeing Special Attention Requirements Bulletin 737-71-1937
RB, dated July 27, 2023, requires the modification of the radial
restraint assembly followed by the installation of the external doubler
on the fan cowl assembly. United Airlines stated that completing the
installation of the external doubler before installation of the new
radial restraint assembly would provide better access to install the
rivets common to the doubler.
The FAA agrees with the commenter's request for the reasons
provided. The FAA coordinated with Boeing, and noted the most
convenient order of modification for operators is to remove the
previous radial restraint, perform the external doubler installation,
and install the modified radial restraint. The FAA has added paragraph
(h)(6) of this AD allowing these two actions to be accomplished
concurrently.
Request To Revise Action Regarding Matching Topcoat
United Airlines noted that Collins Service Bulletin 737NG-71-008,
Revision 4, dated July 28, 2023, states to: ``Topcoat over the repair
area to agree with the initial production topcoat.'' United Airlines
noted that the fan cowl panels are often part of the aircraft livery
and may have switched products and colors several times. Therefore, the
``initial production topcoat'' may conflict with current paint system.
United Airlines added that Table 2.2 of Collins Service Bulletin 737NG-
71-008 Revision 4, dated July 28, 2023, also calls out BMS10-72 Type
VIII topcoat which is not what every operator uses for their exterior
paint system. United Airlines recommended that the step be revised to
``match the surrounding topcoat'' which is generic and allows operators
to use their existing paint system and colors. Alternatively, United
Airlines stated that this step can also be omitted from the RC step
since it is not part of the safety concern being addressed.
The FAA agrees with the commenter for the reasons provided. The FAA
has added paragraph (h)(7) of this AD to permit the topcoat to match
the surrounding topcoat.
Request To Add an Allowance for Substitute to Fastener Length
United Airlines noted that the ability to determine the fastener
grip length during installation for the fan cowl modification is
missing from Boeing Requirements Bulletin 737-71-1937 RB and Collins
Service Bulletin 737NG-71-008. United Airlines requested that the
standard Boeing general note that states ``fasteners of the same
specification, or an approved substitute, with a length that meets the
installation standards given in SRM Chapter 51 may be used'' be added
to the service information. United Airlines noted that installation may
occasionally require a deviation of plus or minus one grip length
adjustment from the fastener part number called out in the service
information due to variations in the stack up (i.e., assembly of
parts).
The FAA agrees to clarify. As previously noted, this AD has been
updated to refer to Boeing Special Attention Requirements Bulletin 737-
71-1937 RB, Revision 1, dated June 27, 2024, which includes the
language United Airlines requested in Note 8. of ``General
Information'' of the Accomplishment Instructions. Therefore, no change
to this AD is necessary.
Effect of Winglets on Accomplishment of the Proposed Actions
Aviation Partners Boeing stated that the installation of winglets
per supplemental type certificate (STC) ST00830SE 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
737-71-1937 RB, Revision 1, dated June 27, 2024. This material
specifies procedures for replacing, for certain airplanes, the
fasteners on the fan cowl support beam hinge fittings on the left and
right engine strut, and, for engine 1 and engine 2 for all airplanes,
modifying the radial restraint assembly and installing an external
doubler at the starter vent, or as an option, installing a serviceable
fan cowl. 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
[[Page 11114]]
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
--------------------------------------------------------------------------------------------------------------------------------------------------------
Action * Labor cost Parts cost Cost per product Cost on U.S. operators
--------------------------------------------------------------------------------------------------------------------------------------------------------
Modification and Installation....... 140 work-hours x $85 $1,400..................... $13,300.................... $26,320,700.
per hour = $11,900.
Fastener replacement................ Up to 8 work-hours x Up to $2,300............... Up to $2,980............... Up to $5,897,420.
$85 per hour = $680.
--------------------------------------------------------------------------------------------------------------------------------------------------------
* The option to install a serviceable fan cowl would cost up to $16,280 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.
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:
2025-04-02 The Boeing Company: Amendment 39-22960; Docket No. FAA-
2023-2234; Project Identifier AD-2023-00963-T.
(a) Effective Date
This airworthiness directive (AD) is effective April 8, 2025.
(b) Affected ADs
None.
(c) Applicability
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 fan cowls
that are not strengthened, which, in the event of an FBO occurrence,
could depart the nacelle potentially damaging a stabilizer, or the
fan cowl 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 737-71-1937 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 737-71-1937 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 737-71-1937, Revision 1, dated June 27, 2024, which is
referred to in Boeing Special Attention Requirements Bulletin 737-
71-1937 RB, Revision 1, dated June 27, 2024.
(h) Exceptions to Service Information Specifications
(1) Where the service information referenced in paragraph (g) of
this AD specifies contacting Boeing or Collins Aerospace for repair
instructions: This AD requires doing the repair before further
flight using a method approved in accordance with the procedures
specified in paragraph (k) of this AD.
(2) Where the Compliance Time columns of the tables in the
``Compliance'' paragraph of Boeing Special Attention Requirements
Bulletin 737-71-1937 RB, Revision 1, dated June 27, 2024, refer to
the original issue date of Requirements Bulletin 737-71-1937 RB,
[[Page 11115]]
this AD requires using the effective date of this AD.
(3) Where System Airworthiness Limitation No. 4, as identified
in Boeing Special Attention Requirements Bulletin 737-71-1937 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.
(4) Where Collins Aerospace Service Bulletin 737NG-71-008
referenced in Boeing Special Attention Requirements Bulletin 737-71-
1937 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.
(5) Where Collins Service Bulletin 737NG-71-008 referenced in
Boeing Special Attention Requirements Bulletin 737-71-1938 RB,
Revision 1, dated June 27, 2024, states to apply primer ``per Boeing
document D6-1816,'' this AD requires replacing that text with ``per
Boeing document D6-1816 or Boeing SOPM 20-41-02.''
(6) Where Boeing Special Attention Requirements Bulletin 737-71-
1937 RB, Revision 1, dated June 27, 2024, requires (Option 1)(Action
3) to be accomplished after (Option 1)(Action 2), this AD allows
these two actions to be accomplished concurrently.
(7) Where Collins Service Bulletin 737NG-71-008, dated July 28,
2023, referenced in Boeing Special Attention Requirements Bulletin
737-71-1938 RB, Revision 1, dated June 27, 2024, specifies to
topcoat over the repair area to agree with the initial production
topcoat, this AD also allows topcoat to match the surrounding
topcoat.
(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 737-71-1937 RB, dated July 27, 2023, provided
where Tables 1 through 4 of Boeing Special Attention Requirements
Bulletin 737-71-1937 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 fastener 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 fastener changes (except for 737.900ER aircraft, because the fan
cowl support beam fastener changes are already incorporated). 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.
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, 2018 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.
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 aircaft 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, 2019.
------------------------------------------------------------------------
(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: [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.
(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: [email protected].
(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 [email protected];
website tpi.beaerospace.com/Authentication.
(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 737-71-1937
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 myboeingfleet.com.
(4) You may view this material at the FAA, Airworthiness
Products Section, Operational Safety Branch, 2200 South 216th St.,
Des
[[Page 11116]]
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 February 25, 2025.
Suzanne Masterson,
Deputy Director, Integrated Certificate Management Division, Aircraft
Certification Service.
[FR Doc. 2025-03395 Filed 3-3-25; 8:45 am]
BILLING CODE 4910-13-P