DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2023-1886; Project Identifier AD-2023-00429-T; 
Amendment 39-22841; AD 2024-18-07]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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

SUMMARY: The FAA is superseding Airworthiness Directive (AD) 2009-01-
02, which applied to certain Boeing Model 737-600, -700, -700C, -800, 
and -900 series airplanes. AD 2009-01-02 required an inspection of 
frames between body station (BS) 360 and BS 907 to determine if certain 
support brackets of the air conditioning (A/C) outlet extrusions are 
installed, inspections for cracking of the frames around the attachment 
holes of the subject brackets, and repair if necessary. AD 2009-01-02 
also requires installing new, improved fittings for all support 
brackets of the A/C outlet extrusions between BS 360 and BS 907. This 
AD was prompted by numerous reports of multiple cracks in the frame 
around the attachment holes of the support bracket of the A/C outlet 
extrusion, and the determination that certain repairs might develop 
fatigue cracks that could result in the inability of the frame to 
sustain limit load and therefore must be inspected. This AD would 
continue to require the actions specified in AD 2009-01-02 and would 
also require repetitive inspections for cracking of certain repairs, 
and repair if necessary. The FAA is issuing this AD to address the 
unsafe condition on these products.

DATES: This AD is effective November 12, 2024.

    The Director of the Federal Register approved the incorporation by 
reference of a certain publication listed in this AD as of November 12, 2024.

    The Director of the Federal Register approved the incorporation by 
reference of a certain other publication listed in this AD as of 
February 27, 2009 (74 FR 4117, January 23, 2009).

ADDRESSES: 

    AD Docket: You may examine the AD docket at regulations.gov under 
Docket No. FAA-2023-1886; 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-2023-1886.

FOR FURTHER INFORMATION CONTACT: Owen F. Bley-Male, Aviation Safety 
Engineer, FAA, 2200 South 216th Street, Des Moines, WA 98198; phone: 
206-231-3992; email: Owen.F.Bley-Male@faa.gov.

SUPPLEMENTARY INFORMATION:

Background

    The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 
CFR part 39 to supersede AD 2009-01-02, Amendment 39-15780 (74 FR 4117, 
January 23, 2009) (AD 2009-01-02). AD 2009-01-02 applied to certain 
Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes. The 
NPRM published in the Federal Register on September 25, 2023 (88 FR 
65637). The NPRM was prompted by numerous reports of multiple cracks in 
the frame around the attachment holes of the support bracket of the A/C 
outlet extrusion and the determination that certain repairs might 
develop fatigue cracks that could result in the inability of the frame 
to sustain limit load and therefore must be inspected. In the NPRM, the 
FAA proposed to continue to require a one-time general visual 
inspection of frames between BS 360 and BS 907 to determine if certain 
support brackets of the A/C outlet extrusions are installed; medium- 
and high-frequency eddy current inspections for cracking of the frames 
around the attachment holes of the subject brackets; repair if 
necessary; and installation of new, improved fittings for all support 
brackets of the A/C outlet extrusions between BS 360 and BS 907. The 
NPRM also proposed to require repetitive inspections for cracking of 
certain repairs, and repair if necessary. The FAA is issuing this AD to 
prevent frame cracking, which, if not corrected, could lead to a severed frame that, 
combined with cracking of the chemically milled steps in the skin above 
the Stringer 10 lap splice, could result in rapid decompression of the airplane.

Discussion of Final Airworthiness Directive

Comments

    The FAA received a comment from an individual who supported the 
NPRM without change.

    The FAA received additional comments from Aviation Partners Boeing, 
The Boeing Company (Boeing), Southwest Airlines (SWA), United Airlines 
(UAL), and an individual. The following presents the comments received 
on the NPRM and the FAA's response to each comment.

Request To Determine Estimated Cost

    An individual commented that the NPRM stated that there is no 
definitive data on which to estimate the labor cost (for the repairs), 
so the basis for this estimated cost is unclear. The commenter 
suggested an estimate using cost data for operations similar to those 
required by this AD, making estimates more robust.

    The FAA cannot pre-determine on-condition actions before the 
inspections required by this AD are actually completed. The work-hours 
to complete repairs will be unique to each airplane. For the other 
actions required by this AD, the FAA used estimated costs that were 
provided by the design approval holder. No changes have been made to 
this AD in this regard.

Effect of Winglets on Accomplishment of the Proposed Actions

    Aviation Partners Boeing stated that incorporation of Supplemental 
Type Certificate (STC) ST00830SE for installation of blended or split 
scimitar winglets does not affect the accomplishment of the 
manufacturer's service instructions.

    The FAA agrees with the commenter that STC ST00830SE does not 
affect the accomplishment of the manufacturer's service instructions. 
Therefore, the installation of 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.

Request for Correction of the Skin Lap Splice Location

    Boeing stated that the NPRM incorrectly identified the location of 
the skin lap splice. The NPRM referred to "cracking of the skin lap 
splice above stringer 10." Boeing requested that language be corrected 
to "cracking of the chemically milled steps in the skin above Stringer 
10 lap splice" to match the language in Boeing Alert Service Bulletin 
737-25A1544, Revision 4, dated February 15, 2022.

    The FAA agrees with the request and has revised the "Background" 
section of this final rule and the "Unsafe Condition" in paragraph 
(e) of this AD accordingly.

Request To Add a General Visual Inspection for Cracks

    Boeing noted that Boeing Alert Service Bulletin 737-25A1544, 
Revision 4, dated February 15, 2022, requires a general visual 
inspection (GVI) to detect cracks, not just to determine if certain 
support brackets of the A/C outlet extrusions are installed at certain 
frames. Boeing requested that a GVI be required to also detect cracks.

    The FAA agrees with the request. The inspections specified in Part 
2 of Boeing Alert Service Bulletin 737-25A1544, Revision 4, dated 
February 15, 2022, include a GVI to detect cracks. The "Material 
Incorporated by Reference under 1 CFR part 51" section of this final 
rule and paragraph (g)(2) of this AD have been revised to include a GVI 
as an inspection method.

Request To Revise the Applicability Statement

    Boeing stated that paragraph (c), "Applicability," of the 
proposed AD incorrectly identified the referenced service information 
as Boeing "Special Attention" Service Bulletin 737-25A1544, Revision 
4, dated February 15, 2022, and explained that Revision 4 of this 
service information is an "alert" service bulletin. The correct 
reference is Boeing Alert Service Bulletin 737-25A1544, Revision 4, 
dated February 15, 2022.

    The FAA agrees and has revised paragraph (c) of this AD accordingly.

Request To Correct Special Attention Service Bulletin

    Boeing stated that a certain Boeing special attention service 
bulletin is incorrectly identified under "Actions Since AD 2009-01-02 
Was Issued" of the NPRM. Boeing pointed out that the NPRM incorrectly 
identified the service bulletin number as "737-25A1544." The correct 
service bulletin number is "737-25-1544."

    The FAA partially agrees. The FAA agrees that the specified service 
bulletin number was stated incorrectly in the NPRM. However, since that 
section of the NPRM is not restated in this final rule, no change is 
necessary in this regard.

Request To Revise AMOC Provisions

    SWA stated that paragraph (j) of the proposed AD requires 
inspection of repairs installed on the BS 907 frame at the compliance 
times given in Table 2 of Boeing Alert Service Bulletin 737-25A1544, 
Revision 4, dated February 15, 2022. SWA mentioned that Table 2 
requires post-repair inspections for repairs that were installed per 
Boeing Special Attention Service Bulletin 737-25-1544, Revision 3, 
dated May 16, 2016; or Boeing Alert Service Bulletin 737-25A1544, 
Revision 4, dated February 15, 2022; and does not address repairs that 
were installed by any other means. SWA proposed revising paragraph 
(m)(4) of the proposed AD to extend alternative method of compliance 
(AMOC) approval to paragraph (j) of the proposed AD, provided the AMOC 
approval contains a damage tolerance evaluation. SWA believes that 
individually approved repairs that contain an AMOC to AD 2009-01-02, 
with a damage tolerance analysis as a Category A or Category B repair 
(as defined in Boeing SRM 51-00-06), provide an equivalent level of 
safety.

    The FAA disagrees with the request. Only repairs installed per 
Boeing Special Attention Service Bulletin 737-25-1544, Revision 3, 
dated May 16, 2016; or Boeing Alert Service Bulletin 737-25A1544, 
Revision 4, dated February 15, 2022; are subject to the requirements of 
paragraph (j) of this AD. Repairs installed by any other means are not 
subject to the requirements of paragraph (j) of this AD, so the 
proposed AMOC to paragraph (j) would not be applicable. The FAA has not 
changed this AD in this regard.

Request To Clarify Airplanes Affected by New Requirements

    UAL supported the NPRM, and requested clarification of the 
airplanes affected by paragraph (j) of the proposed AD. UAL stated that 
some airplanes had repairs to the STA 907 frame performed before 
release of Boeing Special Attention Service Bulletin 737-25-1544, 
Revision 3, dated May 16, 2016. UAL added that these repairs were 
coordinated with Boeing and received Form 8100-9 approvals as AMOCs to 
paragraph (g) of AD 2009-01-02 and are considered Category B damage 
tolerance repairs that also require additional inspections as defined 
in the 8100-9 approval. UAL stated that Table 2 of the "Compliance" 
paragraph of Boeing Alert Service Bulletin 737-25A1544, Revision 4, 
dated February 15, 2022 (as specified in paragraph (j) of the proposed 
AD), applies only to airplanes
on which a frame repair has been done at STA 907 in accordance with 
Boeing Special Attention Service Bulletin 737-25-1544, Revision 3, 
dated May 16, 2016; or Boeing Alert Service Bulletin 737-25-1544, 
Revision 4, dated February 15, 2022. UAL therefore stated that Category 
B repairs via Form 8100-9 should be excluded from paragraph (j) of the 
proposed AD.

    The FAA provides the following clarification. As stated previously, 
only repairs installed per Boeing Special Attention Service Bulletin 
737-25-1544, Revision 3, dated May 16, 2016; or Boeing Alert Service 
Bulletin 747-25A1544, Revision 4, dated February 15, 2022; are subject 
to the requirements of paragraph (j) of this AD. Repairs installed by 
any other means are not subject to the requirements of paragraph (j) of 
this AD. Therefore, no change to this AD is necessary.

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 Alert Service Bulletin 737-25A1544, 
Revision 4, dated February 15, 2022. This material specifies procedures 
for a one-time general visual inspection of frames between BS 360 and 
BS 907 to determine if certain support brackets of the A/C outlet 
extrusions are installed; a general visual inspection and low-, medium-,
and high-frequency eddy current inspections for cracking of the 
frames around the attachment holes of the subject brackets, and repair 
if necessary; and installation of new, improved fittings for all 
support brackets of the A/C outlet extrusions between BS 360 and BS 
907. This material also specifies procedures for repetitive detailed 
and high-frequency eddy current inspections for cracking of certain 
repairs at BS 907 and repair if necessary.

    This AD also requires Boeing Special Attention Service Bulletin 
737-25-1544, Revision 1, dated January 16, 2008, which the Director of 
the Federal Register approved for incorporation by reference as of 
February 27, 2009 (74 FR 4117, January 23, 2009).

    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 738 airplanes of U.S. 
registry. The FAA estimates the following costs to comply with this AD:

                                                                     Estimated Costs

The FAA has received no definitive data on which to base the cost 
estimates for the on-condition repairs that would be required based on 
the results of the inspections specified in this AD.

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

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

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

Sec.  39.13  [Amended]

2. The FAA amends Sec.  39.13 by:

a. Removing Airworthiness Directive (AD) 2009-01-02, Amendment 39-15780 
(74 FR 4117, January 23, 2009); and

b. Adding the following new AD: