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2024-01-06 THE BOEING COMPANY: Amendment 39-22657; Docket No. FAA-2023-1041; Project Identifier AD-2022-01223-T.
(a) EFFECTIVE DATE

    This airworthiness directive (AD) is effective March 7, 2024.

(b) AFFECTED ADS

    None.

(c) APPLICABILITY

    This AD applies to The Boeing Company Model 737-600, 737-700, and 737-
    800 series airplanes,  certificated in any category,  as identified in
    Boeing Alert Service Bulletin 737-53A1217, Revision 1, dated September
    8, 2022.

(d) SUBJECT

    Air Transport Association (ATA) of America Code 53, Fuselage.

(e) UNSAFE CONDITION

    This AD  was prompted  by an evaluation  by the design approval holder
    (DAH) indicating the fuselage skin repairs  at the  double row of fas-
    teners centered on certain stringers  have  inadequate  inspection re-
    quirements for continuing airworthiness  following  repair accomplish-
    ment, which could result in fatigue cracking  of the repair  going un-
    detected. The FAA is issuing this AD to address the inadequacy of post
    -repair inspection requirements  at certain repair fastener  locations
    centered on stringer S-17L and S-17R,  at station (STA) 360 to STA 380
    and at STA 888 to STA 907.  Such inspection inadequacy could result in
    post-repair fatigue cracks going undetected.  Fatigue cracking, if not
    addressed, could grow to a critical length, which could result in rap-
    id decompression and loss of structural integrity of the airplane.

(f) COMPLIANCE

    Comply with this AD within the compliance times specified,  unless al-
    ready done.

(g) REQUIRED ACTIONS

    Except as specified in paragraph (h)  of this AD:  For Group 1 through
    3, Configuration 3 airplanes  as  identified  in  Boeing Alert Service
    Bulletin 737-53A1217, Revision 1,  dated September 8, 2022, at the ap-
    plicable  times  specified  in  Tables 3 through 6  of paragraph 1.E.,
    "Compliance," of Boeing Alert Service Bulletin 737-53A1217, Revision 1
    dated September 8, 2022,  do all applicable actions identified as "RC"
    (required for compliance) in, and in accordance with,  the Accomplish-
    ment Instructions of Boeing  Alert Service Bulletin 737-53A1217, Revi-
    sion 1, dated September 8, 2022.

(h) EXCEPTIONS TO SERVICE INFORMATION SPECIFICATIONS

(1) Where  Boeing  Alert Service Bulletin 737-53A1217,  Revision 1,  dated
    September 8, 2022, specifies contacting Boeing for repair instructions
    or for alternative inspections:  This AD requires doing the repair, or
    doing the alternative inspections and applicable on-condition actions,
    using a method approved in accordance with the procedures specified in
    paragraph (i) of this AD.

(2) Where  Boeing  Alert Service Bulletin 737-53A1217,  Revision 1,  dated
    September 8, 2022, specifies using corrosion inhibiting compound (CIC)
    compound BMS 3-23, this AD also allows use of CIC compound BMS 3-35.

(i) 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 proce-
    dures found in 14 CFR 39.19.  In  accordance  with 14 CFR 39.19,  send
    your request to your principal inspector  or responsible Flight Stand-
    ards Office,  as appropriate.  If sending information  directly to the
    Manager, AIR-520 Continued Operational Safety Branch, FAA,  send it to
    the attention of the person identified in paragraph (j)  of  this  AD.
    Information may be emailed to 9-ANM-Seattle-ACO-AMOC-Requests@faa.gov.

(2) Before using any approved AMOC,  notify your appropriate principal in-
    spector, or lacking a principal inspector,  the manager of the respon-
    sible 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 Oper-
    ational 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.

(4) Except as specified by paragraph (h) of this AD:  For service informa-
    tion that  contains steps  that are labeled as Required for Compliance
    (RC),  the  provisions  of  paragraphs (i)(4)(i)  and  (ii) of this AD
    apply.

(i) The steps labeled as RC,  including substeps  under an RC step and any
    figures identified in an RC step,  must be done to comply with the AD.
    If a step or substep is labeled "RC Exempt,"  then  the RC requirement
    is removed from that step or substep. An AMOC is required for any dev-
    iations to RC steps, including substeps and identified figures.

(ii) Steps not labeled as RC  may be deviated  from using accepted methods
     in accordance with the operator's maintenance  or  inspection program
     without obtaining approval of an AMOC, provided the RC steps, includ-
     ing substeps and identified figures,  can still be done as specified,
     and the airplane can be put back in an airworthy condition.

(j) RELATED INFORMATION

    For more information about this AD,  contact  Bill Ashforth,  Aviation
    Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; tel-
    ephone 206-231-3520; email Bill.Ashforth@faa.gov.

(k) MATERIAL INCORPORATED BY REFERENCE

(1) The Director of the Federal Register  approved  the  incorporation  by
    reference  (IBR)  of the service information  listed in this paragraph
    under 5 U.S.C. 552(a) and 1 CFR part 51.

(2) You must use this service information as applicable  to do the actions
    required by this AD, unless the AD specifies otherwise.

(i) Boeing Alert Service Bulletin 737-53A1217, Revision 1, dated September
    8, 2022.

(ii) [Reserved]

(3) For service information identified in this AD,  contact Boeing Commer-
    cial Airplanes,  Attention:  Contractual & Data Services (C&DS),  2600
    Westminster Blvd., MC 110-SK57,  Seal Beach, CA 90740-5600;  telephone
    562-797-1717; website myboeingfleet.com.

(4) You may view this service information at the FAA,  Airworthiness Prod-
    ucts 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 Admin-
    istration (NARA). For information on the availability of this material
    at NARA,  visit www.archives.gov/federal-register/cfr/ibr-locations or
    email fr.inspection@nara.gov.

Issued on January 6, 2024. Caitlin Locke, Director, Compliance & Airworth-
iness Division, Aircraft Certification Service.

FOR FURTHER INFORMATION CONTACT:  Bill Ashforth, Aviation Safety Engineer,
FAA, 2200 South 216th St.,  Des Moines, WA 98198;  telephone 206-231-3520;
email Bill.Ashforth@faa.gov.
PREAMBLE 

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2023-1041; Project Identifier AD-2022-01223-T;
Amendment 39-22657; AD 2024-01-06]
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
certain The Boeing Company Model 737-600, 737-700, and 737-800 series
airplanes. This AD was prompted by an evaluation by the design approval
holder (DAH) indicating the fuselage skin repairs at the double row of
fasteners centered on certain stringers have inadequate inspection
requirements for continuing airworthiness following repair
accomplishment. This AD is intended to complete certain programs to
support the airplane reaching its limit of validity (LOV). This AD
requires repetitive inspections for cracks of skin repairs at Stringer
S-17, and corrective actions if necessary. The FAA is issuing this AD
to address the unsafe condition on these products.

DATES: This AD is effective March 7, 2024.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of March 7,
2024.

ADDRESSES:
AD Docket: You may examine the AD docket at regulations.gov under
Docket No. FAA-2023-1041; 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 service information identified in this final rule,
contact Boeing Commercial Airplanes, Attention: Contractual & Data
Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA
90740-5600; telephone 562-797-1717; website myboeingfleet.com.
You may view this service information at the FAA,
Airworthiness Products Section, Operational Safety Branch, 2200 South
216th St., Des Moines, WA. For information on the availability of this
material at the FAA, call 206-231-3195. It is also available at
regulations.gov under Docket No. FAA-2023-1041.

FOR FURTHER INFORMATION CONTACT: Bill Ashforth, Aviation Safety
Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; telephone
206-231-3520; email Bill.Ashforth@faa.gov.

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 certain The Boeing
Company (Boeing) Model 737-600, 737-700, and 737-800 series airplanes.
The NPRM was published in the Federal Register on May 25, 2023 (88 FR
33849). The NPRM was prompted by an evaluation by the DAH indicating
the fuselage skin repairs at the double row of fasteners centered on
certain stringers have inadequate inspection requirements for
continuing airworthiness following repair accomplishment, which could
result in fatigue cracking of the repair going undetected.
In the NPRM, the FAA proposed to require repetitive inspections for
cracking of the skin repairs at S-17, and corrective actions if
necessary. The FAA is issuing this AD to address this fatigue cracking,
which, if not addressed, could grow to a critical length and result in
rapid decompression and loss of the airplane's structural integrity.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from the Air Line Pilots Association,
International (ALPA) who supported the NPRM without change.
The FAA also received comments from Aviation Partners Boeing (APB),
Boeing, Southwest Airlines (Southwest), and SunExpress Airline
(SunExpress).

Compliance With AMOC Procedures

APB determined that the incorporation of supplemental type
certificate (STC) ST00830SE for installation of split scimitar winglets
affects compliance with the mandated actions in the proposed rule, but
the extent of the impact to compliance is not fully known at this time.
APB noted that paragraph (h) of the proposed AD would replace the
provisions in Boeing Service Bulletin 737-53A1217 R1 that specify
contacting Boeing for an alternative method of compliance (AMOC) for
alternative inspections and corrective actions, and instead would
require using a method approved in accordance with paragraph (i) of the
proposed AD. APB stated that for affected airplanes with these
winglets, approval of any alternative inspections and corrective
actions for Zone 3 and Zone 4 repairs must be obtained from the
Manager, AIR-520 Continued Operational Safety Branch, FAA, through the
means described in paragraph (i)(1) of the proposed AD. APB asserted
that Boeing does not have delegation to approve repairs in areas
affected by the configuration of STC ST00830SE and cannot use ODA
approval as specified in paragraph (i)(3) of the proposed AD.
The FAA acknowledges APB's comment. Paragraph (h)(1) of this AD
states that AMOC approval be obtained using a method approved in
accordance with the procedures specified in ``paragraph (i)'' of this
AD, and does not limit approvals to the provisions of paragraph (i)(1)
or (3) of this AD. Therefore, no change to this AD is necessary.

Request To Correct Service Bulletin Reference

Boeing reported that the Background section of the NPRM incorrectly
identified the original service information as Boeing Service Bulletin
``737-53A1217,'' but that document was not an alert service bulletin
and should have been identified as Service Bulletin ``737-53-1217.''
The FAA agrees; no change to the final rule is necessary because
that reference is not used.

Request To Specify Service Bulletin Revision Level

The NPRM's Background section explained that certain existing post-
repair inspections are inadequate to address the unsafe condition, and
that the actions in paragraph (g) of the proposed AD would apply only
to airplanes on which a repair has been done as specified in ``Boeing
Alert Service Bulletin 737-53A1217.'' Boeing requested that the
statement be clarified by adding the revision level and date of the
service bulletin. Boeing further stated that Boeing Alert Service
Bulletin 737-53A1217, Revision 1, dated September 8, 2022, was issued
to add the post-repair inspections to airplanes on which a repair has
been done.
The FAA disagrees. In this context, the revision level and date of
the service bulletin were intentionally omitted so the Background
section of the NPRM would refer to any repair-including a repair done
using a method other than the service bulletin (at any revision level).
No change is necessary to this final rule.

Request To Revise Unsafe Condition

Boeing requested changes to paragraph (e) of the proposed AD, which
implied the unsafe condition is the potential for cracking. Boeing
stated that the proposed AD would require only post-repair inspections,
and asserted that the unsafe condition is actually the lack of post-
repair inspections because it could result in undetected post-repair
fatigue cracks.
The FAA agrees and has incorporated the relevant changes.

Request To Revise Compliance Time


Southwest and SunExpress stated that Boeing Alert Service Bulletin
737-53A1217 provides no grace period for airplanes that have exceeded
the threshold, and requested that the proposed AD be revised to provide
a grace period or optional threshold value.
The FAA notes that paragraph (g) of this AD mandates only Tables 3
through 6 of paragraph 1.E., ``Compliance,'' of Boeing Alert Service
Bulletin 737-53A1217, Revision 1, dated September 8, 2022. For those
actions, the service bulletin specifies a compliance time of 50,000
total flight cycles, with a grace period of 4,000 flight cycles after
the repair. Therefore, no change is necessary to the AD.

Request To Clarify Configuration Description

Southwest requested clarification of the affected airplanes and
corresponding requirements for Tables 1 through 3 of Boeing Alert
Service Bulletin 737-53A1217, Revision 1, dated September 8, 2022.
Southwest noted that paragraphs 1.A.1. and 1.D. define Groups 1 through
3, Configuration 3, as ``airplanes that have installed a repair,'' but
tables 1 through 3 of paragraph 1.E list conditions for airplanes that
both have and have not accomplished a repair.
The FAA provides the following clarification. The tables apply to
any airplanes that have performed a repair, whether the repair was done
in accordance with ``SB 737-53-1217 Original Issue'' or in accordance
with some other method. So the condition ``Airplanes that have not
accomplished a repair in accordance with `SB 737-53-1217 Original
Issue' applies to airplanes that have been repaired using some method
other than `SB 737-53-1217 Original Issue.' '' Groups 1 through 3,
Configuration 3, include any airplane on which a repair has been
accomplished in one of the zones specified in the service information.
No changes to this AD are necessary as a result of this comment.

Request To Use BMS 3-35 or BMS 3-23 Compound

Southwest noted that Boeing Alert Service Bulletin 737-53A1217,
Revision 1, dated September 8, 2022, specifies the use of BMS 3-23
corrosion-inhibiting compound (CIC) for repairs. Southwest requested
that the proposed AD be revised to allow the use of BMS 3-35 CIC due to
the faster drying time compared to BMS 3-23 CIC. Southwest stated that
Boeing Corrosion Prevention Manual (CPM) 20-60-00 and Boeing Service
Request (SR) SWA-SWA-10-1232-02B approve BMS 3-35 for use on all Boeing
commercial airplanes including those no longer in production.
The FAA agrees that either BMS 3-35 or BMS 3-23 CIC is acceptable
because both provide an adequate level of safety. Paragraph (h)(2) of
this AD has been added to allow use of either CIC.

Conclusion

The FAA reviewed the relevant data, considered the received
comments, and determined that air safety requires adopting this AD as
proposed, with limited changes as previously stated. 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.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Boeing Alert Service Bulletin 737-53A1217,
Revision 1, dated September 8, 2022. This service information specifies
procedures for, among other actions, repetitive internal and external
detailed inspections, low frequency eddy current (LFEC) inspections,
and medium frequency eddy current (MFEC) inspections for cracks of the
skin repair of S-17, station (STA) 360 to STA 380, and STA 888 to STA
907, left and right sides of the airplane. Corrective actions include
repair. This service information is reasonably available because the
interested parties have access to it through their normal course of
business or by the means identified in ADDRESSES.

Costs of Compliance

The FAA estimates that this AD affects 106 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
External Post Repair Inspection 56 work-hours x $85 per hour = $4,760 per inspection cycle $0 $4,760 per inspection cycle $504,560 per inspection cycle
Internal Post Repair Inspections 52 work-hours x $85 per hour = $4,420 per inspection cycle 0 $4,420 per inspection cycle $468,520 per inspection cycle

The FAA has received no definitive data on which to base the cost
estimates for the repairs 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 adding the following new airworthiness
directive: