
[Federal Register Volume 88, Number 183 (Friday, September 22, 2023)]
[Rules and Regulations]
[Pages 65305-65308]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-20503]



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 Rules and Regulations
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  Federal Register / Vol. 88, No. 183 / Friday, September 22, 2023 / 
Rules and Regulations  

[[Page 65305]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2022-1250; Project Identifier AD-2022-00763-T; 
Amendment 39-22490; AD 2023-13-05]
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 a report indicating fuselage 
skin lap splice cracking was found between stations (STA) 767 and STA 
787, just below S-14R fuselage skin lap splice, where a lower skin 
panel buckle intersected the upper skin of the lap splice. Cracking was 
also found just below S-14R between STA 747 and STA 767. This AD 
requires an inspection for any repair at certain skin lap splices at S-
4, S-14, and S-24 and depending on the configuration, repetitive 
inspections for buckling, wrinkling, or bulging at affected skin lap 
splices and repair, repetitive inspections for cracking at affected 
locations common to fuselage skin on the left and right sides and 
repair, and alternative inspections and on-condition actions. The FAA 
is issuing this AD to address the unsafe condition on these products.

DATES: This AD is effective October 27, 2023.
    The Director of the Federal Register approved the incorporation by 
reference of a certain publication listed in this AD as of October 27, 
2023.

ADDRESSES: 
    AD Docket: You may examine the AD docket at regulations.gov under 
Docket No. FAA-2022-1250; 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-2022-1250.

FOR FURTHER INFORMATION CONTACT: Owen Bley-Male, Aviation Safety 
Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206-
231-3992; 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 November 9, 2022 (87 FR 
67581). The NPRM was prompted by a report indicating fuselage skin lap 
splice cracking was found between STA 767 and STA 787, just below S-14R 
fuselage skin lap splice, where a lower skin panel buckle intersected 
the upper skin of the lap splice. Cracking was also found just below S-
14R between STA 747 and STA 767. In the NPRM, the FAA proposed to 
require an inspection for any repair at certain skin lap splices and 
depending on the configuration, repetitive inspections for buckling, 
wrinkling, or bulging at affected skin lap splices and repair, 
repetitive inspections for cracking at affected locations common to 
fuselage skin on the left and right sides and repair, and alternative 
inspections and on-condition actions. The FAA is issuing this AD to 
address cracks, skin buckles, wrinkles, and bulges at fuselage 
longitudinal lap splice areas at S-4, S-14 and S-24. This condition, if 
not addressed, could result in cracks in fatigue-critical baseline 
structure and the inability of a principal structural element to 
sustain limit loads, which could adversely affect the structural 
integrity of the airplane.

Discussion of Final Airworthiness Directive

Comments

    The FAA received a comment from The Air Line Pilots Association, 
International, who supported the NPRM without change.
    The FAA received additional comments from six commenters, including 
Boeing, Aviation Partners Boeing, Delta Air Lines (Delta), Southwest 
Airlines (SWA), United Airlines (UAL), and Qantas. The following 
presents the comments received on the NPRM and the FAA's response to 
each comment.

Effect of Winglets on Accomplishment of the Proposed Actions

    Aviation Partners Boeing stated that accomplishing Supplemental 
Type Certificate (STC) ST00830SE does not affect the actions specified 
in the proposed AD.
    The FAA concurs with the commenter. The FAA has redesignated 
paragraph (c) of the proposed AD as paragraph (c)(1) of this AD and 
added paragraph (c)(2) to this AD to state that installation of STC 
ST00830SE does not affect the ability to accomplish the actions 
required by this AD. Therefore, for airplanes on which STC ST00830SE is 
installed, a ``change in product'' alternative method of compliance 
(AMOC) approval request is not necessary to comply with the 
requirements of 14 CFR 39.17

Request To Correct Errors in Service Information or Refer to Latest 
Service Information

    Boeing, Delta, SWA, UAL, and Qantas requested that the NPRM be 
revised to correct errors in the referenced service information. 
Boeing, SWA, UAL, and Qantas requested that the NPRM be

[[Page 65306]]

revised to refer to a new revision of Boeing Special Attention 
Requirements Bulletin 737-53-1399 RB, dated May 20, 2022. The 
commenters noted that Boeing was drafting a revision to correct several 
errors in the service information. Boeing stated that the revision 
would modify a table and several illustrations, inspection steps, and 
footnotes to clarify the inspection locations, and revise Table 1 in 
the Accomplishment Instructions to correctly specify the applicable 
airplanes. SWA suggested the revision would clarify the distinction 
between the detailed visual and non-destructive testing (NDT) 
inspections underneath the lap joint. UAL and SWA noted that certain 
figures incorrectly specify to externally inspect an area that is not 
visible externally. UAL added that the revision would correct errors in 
the figures related to orientations of airplane sections. Delta and 
Qantas noted that Table 1 of the Accomplishment Instructions of Boeing 
Special Attention Requirements Bulletin 737-53-1399 RB, dated May 20, 
2022, includes the compliance actions for Groups 1 through 6 airplanes, 
but Table 1 specifies it applies only to Group 1 airplanes. UAL pointed 
out that Table 1 in the Compliance section specifies the inspections 
are applicable to all airplanes, which contradicts Table 1 in the 
Accomplishment Instructions of Boeing Special Attention Requirements 
Bulletin 737-53-1399 RB, dated May 20, 2022.
    The FAA agrees with the commenters' request. The FAA has reviewed 
Boeing Special Attention Requirements Bulletin 737-53-1399 RB, Revision 
1, dated March 14, 2023, which corrects the errors noted by the 
commenters. Boeing Special Attention Requirements Bulletin 737-53-1399 
RB, Revision 1, dated March 14, 2023, also combines actions for several 
conditions to remove duplicative instructions and revises related 
figures accordingly. These revisions allow operators to do all 
applicable actions for their airplane models without obtaining an AMOC, 
and do not add additional work. The FAA has revised this AD to refer to 
Boeing Special Attention Requirements Bulletin 737-53-1399 RB, Revision 
1, dated March 14, 2023.

Request To Clarify Inspection Locations

    Boeing requested that the FAA revise the Related Service 
Information Under 1 CFR part 51 section of the NPRM to clarify the 
inspection locations, including whether they are on the right (R) or 
left (L) side of the airplane, and applicable airplane models for each 
inspection location. Boeing noted that the locations specified in the 
NPRM don't correspond to the service information due to errors in 
Boeing Special Attention Requirements Bulletin 737-53-1399 RB, dated 
May 20, 2022.
    The FAA agrees to revise the Related Service Information Under 1 
CFR part 51 section for the reasons provided. The FAA has revised this 
section as requested.

Request To Clarify Root Cause of Cracking

    Boeing asked that the FAA change a sentence in the Background 
section of the NPRM to specify that the skin lap splice cracking ``may 
have been the result of incorrect procedures . . .'' rather than ``was 
the result of incorrect procedures . . .'' Boeing noted that it has 
always stated that the root cause of cracking is unknown.
    The FAA agrees that the suggested wording provides clarification on 
the root cause. However, the sentence in question does not get carried 
over to the final rule. This AD was not changed regarding this issue.

Request To Clarify Number of Reports

    Boeing requested that the FAA revise a sentence in the Background 
section of the NPRM to specify that the FAA ``received a report from 
Boeing'' rather than ``received reports'' indicating fuselage skin 
cracking was found. Boeing noted that it had only one report of crack 
findings, with only one airplane with cracks reported.
    The FAA agrees that the suggested wording is more accurate. 
However, the sentence in question does not get carried over to the 
final rule. This AD was not changed regarding this issue.

Request To Remove Reference to Widespread Fatigue Damage (WFD)

    Boeing requested that the FAA revise the proposed AD to remove 
reference to WFD. Boeing explained that, although there was one report 
of multi-site damage within two bays, it does not consider this 
cracking to be a WFD issue. Boeing added that, based on its reviews of 
similar manufactured skins on other models of Boeing airplanes, these 
skins are not susceptible to WFD. Additionally, Boeing proposed revised 
language for the unsafe condition sentence in the proposed AD.
    The FAA agrees with the commenter's request. After further review, 
the FAA has determined that a single crack finding is not enough to 
conclusively indicate that the unsafe condition is related to WFD. 
However, an unsafe condition still exists because cracks in fatigue-
critical baseline structure and the inability of a principal structural 
element to sustain limit loads could adversely affect the structural 
integrity of the airplane. The FAA has revised the SUMMARY, Background 
section, and paragraph (e) of this AD to remove reference to WFD, and 
revised the Background section and paragraph (e) of this AD to clarify 
the unsafe condition.

Request To Define Skin Buckles, Wrinkles, and Bulges

    Qantas requested that the proposed AD be revised to provide more 
precise definitions for skin buckles, wrinkles, and bulges, including 
size, orientation, origin, and depth as well as whether wrinkling is 
permanent or temporary. Qantas noted that skin panels have minor 
imperfections due to production assembly processes, but those aren't 
skin buckles, wrinkles, or bulges. Qantas states that what constitutes 
a skin buckle, wrinkle, or bulge could be open to interpretation, 
causing operators to perform unnecessary NDT inspection. The commenter 
noted that it found a Boeing definition of a buckle and a Boeing 
Service Letter that states wrinkling is temporary and will have no 
detrimental long-term effect unless it becomes more severe or 
permanent. The commenter added that the Boeing Service Letter suggests 
that you'll find wrinkling in the vicinity of the inspection area. 
Qantas suggested this would lead to unnecessary repeat inspection on 
unrepaired areas and cause an undue burden.
    The FAA acknowledges the commenter's concern. This terminology 
reflects the suspected root cause of the discovered cracking, and 
possible precursors to future cracks. This terminology also reflects 
commonly used verbiage for possible structural damage, so further 
explanation is unnecessary. However, the FAA notes that Boeing Special 
Attention Requirements Bulletin 737-53-1399 RB, Revision 1, dated March 
14, 2023, states that areas of loose paint, discoloration, loose 
fasteners, lap joint separation, or disturbed sealant can be indicative 
of areas where a skin buckle, wrinkle, or bulge has occurred. Skin 
buckles, wrinkles, or bulges could lead to cracks that may result in 
the inability of a principal structural element to sustain limit load, 
which could result in reduced structural integrity of the airplane and 
lead to a decompression event. Therefore, the follow-on inspections for 
cracks are necessary if any skin buckles, wrinkles, or bulges are 
found, regardless of size, origin, depth, or other factors. This AD was 
not changed regarding this issue.

[[Page 65307]]

Request To Revise Certain Compliance Times

    Qantas noted that, for certain conditions, the NDT inspections must 
be repeated every 600 flight cycles, regardless whether any buckle, 
wrinkle, or bulge is found, which is burdensome for operators. The FAA 
infers the commenter is requesting an extension of the compliance time.
    The FAA disagrees with the commenter's request. In developing the 
compliance times for this AD, the FAA considered the recommendations of 
the manufacturer as well as the urgency associated with the subject 
unsafe condition. However, under the provisions of paragraph (i) of 
this AD, the FAA will consider requests for approval of an extension of 
the compliance time if sufficient data are submitted to substantiate 
that the new compliance time would provide an acceptable level of 
safety. This AD was not changed regarding this issue.

Request To Clarify Paint Thickness for Certain Inspections

    SWA requested clarification regarding the acceptable level of paint 
thickness for certain inspections. SWA noted that figures 17 through 19 
and 28 through 35 in Boeing Special Attention Requirements Bulletin 
737-53-1399 RB, dated May 20, 2022, indicate that subsequent NDT 
inspections can be accomplished with paint in place. SWA added that per 
the 737 NDT Manual Part 4, 53-30-06, the procedure can only be used 
with paint up to 0.007 inches thick. SWA suggested adding this guidance 
in a note, since the repetitive inspections occur every 600 flight 
cycles.
    The FAA notes that the suggested clarification has been added to a 
note in the applicable figures in Boeing Special Attention Requirements 
Bulletin 737-53-1399 RB, Revision 1, dated March 14, 2023. As 
previously noted, this AD has been revised to refer to Boeing Special 
Attention Requirements Bulletin 737-53-1399 RB, Revision 1, dated March 
14, 2023. Therefore, no further change to this AD is necessary 
regarding this issue.

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.

Related Service Information Under 1 CFR Part 51

    The FAA reviewed Boeing Special Attention Requirements Bulletin 
737-53-1399 RB, Revision 1, dated March 14, 2023. This service 
information specifies procedures for a general visual inspection for 
any repair, any buckle, any wrinkle, any bulge, and any cracking at 
skin lap splice at stringers S-4R (737-800 Boeing Converted Freighter 
airplanes only), S-14L, S-14R, and S-24R (737-600, -700, -700C, 800, -
900, and -900ER series airplanes only). This service information also 
describes procedures, depending on the configuration, for repetitive 
detailed inspections for buckling, wrinkling, or bulging at unrepaired 
areas of affected lap splices, and repair; repetitive detailed, high 
frequency eddy current (HFEC), and ultrasonic (UT) inspections for 
cracking at affected locations common to fuselage skin on the left and 
right sides, and repair; and alternative inspections and on-condition 
actions. 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 2,462 airplanes of U.S. 
registry. The FAA estimates the following costs to comply with this AD:

                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                                                 Cost on U.S.
             Action                      Labor cost          Parts cost    Cost per product        operators
----------------------------------------------------------------------------------------------------------------
Inspections.....................  Up to 34 work-hours x              $0  $2,890 per           Up to $7,115,180
                                   $85 per hour = Up to                   inspection cycle.    per inspection
                                   $2,890 per inspection                                       cycle.
                                   cycle.
----------------------------------------------------------------------------------------------------------------

    The FAA has received no definitive data on which to base the cost 
estimates for the on-condition repairs or for the alternative 
inspections and on-condition actions 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:

[[Page 65308]]

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:

2023-13-05 The Boeing Company: Amendment 39-22490; Docket No. FAA-
2022-1250; Project Identifier AD-2022-00763-T.

(a) Effective Date

    This airworthiness directive (AD) is effective October 27, 2023.

(b) Affected ADs

    None.

(c) Applicability

    (1) This AD applies to all The Boeing Company Model 737-600, -
700, -700C, -800, -900, and -900ER series airplanes, certificated in 
any category.
    (2) Installation of Supplemental Type Certificate (STC) 
ST00830SE does not affect the ability to accomplish the actions 
required by this AD. Therefore, for airplanes on which STC ST00830SE 
is installed, a ``change in product'' alternative method of 
compliance (AMOC) approval request is not necessary to comply with 
the requirements of 14 CFR 39.17

(d) Subject

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

(e) Unsafe Condition

    This AD was prompted by a report indicating fuselage skin lap 
splice cracking was found between stations (STA) 767 and STA 787, 
just below S-14R fuselage skin lap splice, where a lower skin panel 
buckle intersected the upper skin of the lap splice. Cracking was 
also found just below S-14R between STA 747 and STA 767. The FAA is 
issuing this AD to address cracks, skin buckles, wrinkles, and 
bulges at fuselage longitudinal lap splice areas at S-4, S-14 and S-
24. This condition, if not addressed, could result in cracks in 
fatigue-critical baseline structure and the inability of a principal 
structural element to sustain limit loads, which could adversely 
affect the structural integrity of the airplane.

(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 737-53-1399 RB, Revision 1, 
dated March 14, 2023, do all applicable actions identified in, and 
in accordance with, the Accomplishment Instructions of Boeing 
Special Attention Requirements Bulletin 737-53-1399 RB, Revision 1, 
dated March 14, 2023.

    Note 1 to paragraph (g):  Guidance for accomplishing the actions 
required by this AD can be found in Boeing Special Attention Service 
Bulletin 737-53-1399 RB, Revision 1, dated March 14, 2023, which is 
referred to in Boeing Special Attention Requirements Bulletin 737-
53-1399 RB, Revision 1, dated March 14, 2023.

(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 737-53-1399 RB, Revision 1, dated March 14, 2023, use the 
phrase ``the original issue date of the Requirements Bulletin 737-
53-1399 RB,'' this AD requires using ``the effective date of this 
AD.''
    (2) Where Boeing Special Attention Requirements Bulletin 737-53-
1399 RB, Revision 1, dated March 14, 2023, specifies contacting 
Boeing for repair instructions or for alternative inspections: This 
AD requires doing the repair and 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.

(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 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 
(j)(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.

(j) Related Information

    (1) For more information about this AD, contact Owen Bley-Male, 
Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 
98198; phone: 206-231-3992; email: [email protected].
    (2) Service information identified in this AD that is not 
incorporated by reference is available at the addresses specified in 
paragraphs (k)(3) and (4) of this AD.

(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 Special Attention Requirements Bulletin 737-53-1399 
RB, Revision 1, dated March 14, 2023.
    (ii) [Reserved]
    (3) For service information identified in this AD, contact 
Boeing Commercial Airplanes, Attention: Contractual & Data Services 
(C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-
5600; telephone 562-797-1717; internet myboeingfleet.com.
    (4) 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.
    (5) You may view this service information that is incorporated 
by reference at the National Archives and Records Administration 
(NARA). For information on the availability of this material at 
NARA, [email protected], or go to: www.archives.gov/federal-register/cfr/ibr-locations.html.

    Issued on June 30, 2023.
Michael Linegang,
Acting Director, Compliance & Airworthiness Division, Aircraft 
Certification Service.
[FR Doc. 2023-20503 Filed 9-21-23; 8:45 am]
BILLING CODE 4910-13-P


