Document ID: FAA-2021-0665-0001
Agency: faa
Document Type: Proposed Rule
Title: Airworthiness Directives: The Boeing Company Airplanes
Posted Date: 2021-08-24T04:00Z

[Federal Register Volume 86, Number 161 (Tuesday, August 24, 2021)]
[Proposed Rules]
[Pages 47260-47264]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-18068]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2021-0665; Project Identifier AD-2021-00270-T]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to supersede Airworthiness Directive (AD) 
2017-23-02, which applies to certain The Boeing Company Model 737-200, 
-200C, -300, -400, and -500 series airplanes. AD 2017-23-02 requires

[[Page 47261]]

repetitive inspections, replacement, and applicable on-condition 
actions for certain fuselage crown skin panels. Since the FAA issued AD 
2017-23-02, certain airplane configurations and inspection locations 
have been revised and additional airplanes have been determined to be 
subject to the unsafe condition. This proposed AD would retain the 
actions in AD 2017-23-02, revise certain airplane configurations and 
inspection locations, and add airplanes to the applicability. The FAA 
is proposing this AD to address the unsafe condition on these products.

DATES: The FAA must receive comments on this proposed AD by October 8, 
2021.

ADDRESSES: You may send comments, using the procedures found in 14 CFR 
11.43 and 11.45, by any of the following methods:
     Federal eRulemaking Portal: Go to https://www.regulations.gov. Follow the instructions for submitting comments.
     Fax: 202-493-2251.
     Mail: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue SE, Washington, DC 20590.
     Hand Delivery: Deliver to Mail address above between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    For service information identified in this NPRM, 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 https://www.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 https://www.regulations.gov 
by searching for and locating Docket No. FAA-2021-0665.

Examining the AD Docket

    You may examine the AD docket at https://www.regulations.gov by 
searching for and locating Docket No. FAA-2021-0665; 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 NPRM, any comments 
received, and other information. The street address for Docket 
Operations is listed above.

FOR FURTHER INFORMATION CONTACT: James Guo, Aerospace Engineer, 
Airframe Section, FAA, Los Angeles ACO Branch, 3960 Paramount 
Boulevard, Lakewood, CA 90712-4137; phone: 562-627-5357; fax: 562-627-
5210; email: james.guo@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA invites you to send any written relevant data, views, or 
arguments about this proposal. Send your comments to an address listed 
under ADDRESSES. Include ``Docket No. FAA-2021-0665; Project Identifier 
AD-2021-00270-T'' at the beginning of your comments. The most helpful 
comments reference a specific portion of the proposal, explain the 
reason for any recommended change, and include supporting data. The FAA 
will consider all comments received by the closing date and may amend 
the proposal because of those comments.
    Except for Confidential Business Information (CBI) as described in 
the following paragraph, and other information as described in 14 CFR 
11.35, the FAA will post all comments received, without change, to 
https://www.regulations.gov, including any personal information you 
provide. The agency will also post a report summarizing each 
substantive verbal contact received about this proposed AD.

Confidential Business Information

    CBI is commercial or financial information that is both customarily 
and actually treated as private by its owner. Under the Freedom of 
Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public 
disclosure. If your comments responsive to this NPRM contain commercial 
or financial information that is customarily treated as private, that 
you actually treat as private, and that is relevant or responsive to 
this NPRM, it is important that you clearly designate the submitted 
comments as CBI. Please mark each page of your submission containing 
CBI as ``PROPIN.'' The FAA will treat such marked submissions as 
confidential under the FOIA, and they will not be placed in the public 
docket of this NPRM. Submissions containing CBI should be sent to James 
Guo, Aerospace Engineer, Airframe Section, FAA, Los Angeles ACO Branch, 
3960 Paramount Boulevard, Lakewood, CA 90712-4137; phone: 562-627-5357; 
fax: 562-627-5210; email: james.guo@faa.gov. Any commentary that the 
FAA receives which is not specifically designated as CBI will be placed 
in the public docket for this rulemaking.

Background

    Fatigue damage can occur locally, in small areas or structural 
design details, or globally, in widespread areas. Multiple-site damage 
is widespread damage that occurs in a large structural element such as 
a single rivet line of a lap splice joining two large skin panels. 
Widespread damage can also occur in multiple elements such as adjacent 
frames or stringers. Multiple-site damage and multiple-element damage 
cracks are typically too small initially to be reliably detected with 
normal inspection methods. Without intervention, these cracks will 
grow, and eventually compromise the structural integrity of the 
airplane. This condition is known as widespread fatigue damage (WFD). 
It is associated with general degradation of large areas of structure 
with similar structural details and stress levels. As an airplane ages, 
WFD will likely occur, and will certainly occur if the airplane is 
operated long enough without any intervention.
    An FAA final rule (``Aging Airplane Program: Widespread Fatigue 
Damage;'' 75 FR 69746, November 15, 2010) became effective on January 
14, 2011, and amended 14 CFR parts 25, 26, 121, and 129 (commonly known 
as the WFD rule). The WFD rule requires certain actions to prevent 
structural failure due to WFD throughout the operational life of 
certain existing transport category airplanes and all of these 
airplanes that will be certificated in the future. Design approval 
holders (DAHs) of existing and future airplanes subject to the WFD rule 
are required to establish a limit of validity (LOV) of the engineering 
data that support the structural maintenance program. Operators 
affected by the WFD rule may not fly an airplane beyond its LOV, unless 
an extended LOV is approved.
    The WFD rule does not require identifying and developing 
maintenance actions if the DAHs can show that such actions are not 
necessary to prevent WFD before the airplane reaches the LOV. Many 
LOVs, however, do depend on accomplishment of future maintenance 
actions. As stated in the WFD rule, any maintenance actions necessary 
to reach the LOV will be mandated by airworthiness directives through 
separate rulemaking actions.
    In the context of WFD, this action is necessary to enable DAHs to 
propose LOVs that allow operators the longest operational lives for 
their airplanes, and still ensure that WFD will not occur. This 
approach allows for an implementation strategy that provides 
flexibility to DAHs in determining the timing of service information 
development (with FAA approval), while providing operators with 
certainty

[[Page 47262]]

regarding the LOV applicable to their airplanes.
    The FAA issued AD 2017-23-02, Amendment 39-19096 (82 FR 52835, 
November 15, 2017) (AD 2017-23-02), for certain The Boeing Company 
Model 737-200, -200C, -300, -400, and -500 series airplanes. AD 2017-
23-02 was prompted by an evaluation by the DAH indicating that the 
fuselage crown skin panels are subject to WFD. AD 2017-23-02 requires 
repetitive inspections, replacement, and applicable on-condition 
actions for certain fuselage crown skin panels. The agency issued AD 
2017-23-02 to address cracking in the fuselage crown skin panels. 
Multiple adjacent cracks in the fuselage crown skin could link up and 
lead to decompression or loss of structural integrity of the airplane.

Actions Since AD 2017-23-02 Was Issued

    Since the FAA issued AD 2017-23-02, errors were found in Boeing 
Alert Service Bulletin 737-53A1358, dated April 27, 2017, which is 
referenced in AD 2017-23-02. These errors include airplanes that are 
incorrectly identified as being in certain groups, and inspection 
figures that show incorrect chem-mill locations. Additional airplanes 
were also identified as being subject to the unsafe condition. These 
errors affect operators' ability to comply with AD 2017-23-02, and the 
FAA determined that a supersedure was needed to require corrected 
service information.

FAA's Determination

    The FAA is issuing this NPRM after determining that the unsafe 
condition described previously is likely to exist or develop on other 
products of the same type design.

Related Service Information Under 1 CFR Part 51

    The FAA reviewed Boeing Alert Service Bulletin 737-53A1358, 
Revision 1, dated February 26, 2021. This service information specifies 
procedures for repetitive non-destructive inspections for cracking, 
replacement of certain fuselage crown skin panels, and applicable on-
condition actions. On-condition actions include a general visual 
inspection of certain repairs for any loose or missing fasteners, a low 
frequency eddy current (LFEC) inspection of certain repairs for 
cracking, and 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 the ADDRESSES section.

Proposed AD Requirements in This NPRM

    Although this proposed AD does not explicitly restate the 
requirements of AD 2017-23-02, this AD would retain all of the 
requirements of AD 2017-23-02. Those requirements are referenced in the 
service information identified previously, which, in turn, is 
referenced in paragraph (h) of this proposed AD. This proposed AD would 
revise certain airplane configurations and inspection locations, and 
add airplanes to the applicability. This proposed AD would also require 
accomplishment of the actions identified as ``RC'' (required for 
compliance) in the Accomplishment Instructions of Boeing Alert Service 
Bulletin 737-53A1358, Revision 1, dated February 26, 2021, described 
previously, except for any differences identified as exceptions in the 
regulatory text of this proposed AD.
    For information on the procedures and compliance times, see this 
service information at https://www.regulations.gov by searching for and 
locating Docket No. FAA-2021-0665.

Explanation of Proposed Compliance Time

    The compliance time for the replacement specified in this proposed 
AD for addressing WFD was established to ensure that discrepant 
structure is replaced before WFD develops in airplanes. Standard 
inspection techniques cannot be relied on to detect WFD before it 
becomes a hazard to flight. The FAA will not grant any extensions of 
the compliance time to complete any AD-mandated service bulletin 
related to WFD without extensive new data that would substantiate and 
clearly warrant such an extension.

Explanation of Proposed Applicability

    Model 737 airplanes having line numbers 1 through 291 have an LOV 
of 34,000 total flight cycles, and the actions proposed in this NPRM, 
as specified in Boeing Alert Service Bulletin 737-53A1358, Revision 1, 
dated February 26, 2021, would be required at a compliance time 
occurring after that LOV. Although operation of an airplane beyond its 
LOV is prohibited by 14 CFR 121.1115 and 129.115, this NPRM would 
include those airplanes in the applicability so that these airplanes 
are tracked in the event the LOV is extended in the future.

Costs of Compliance

    The FAA estimates that this AD, if adopted as proposed, would 
affect 143 airplanes of U.S. registry. The FAA estimates the following 
costs to comply with this proposed AD:

                                                 Estimated Costs
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                                                                                                 Cost on U.S.
             Action                     Labor cost          Parts cost     Cost per  product       operators
----------------------------------------------------------------------------------------------------------------
Inspection.....................  Up to 507 work-hours x               $0  Up to $43,095 per   Up to $6,162,585
                                  $85 per hour = Up to                     inspection cycle.   per inspection
                                  $43,095 per inspection                                       cycle.
                                  cycle.
Replacement....................  304 work-hours x $85             95,000  $120,840 per skin   $17,280,120 per
                                  per hour = $25,840 per                   panel.              skin panel.
                                  skin panel.
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    The FAA estimates the following costs to do any necessary 
inspections that would be required based on the results of the proposed 
inspection. The FAA has no way of determining the number of aircraft 
that might need these inspections:

                                               On-Condition Costs
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                                                                                                     Cost per
                   Action                                 Labor cost                Parts cost        product
----------------------------------------------------------------------------------------------------------------
LFEC inspection............................  1 work-hours x $85 per hour = $85..              $0             $85

[[Page 47263]]

 
General visual inspection..................  1 work-hour x $85 per hour = $85...               0              85
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    The FAA has received no definitive data on which to base the cost 
estimates for the on-condition repairs specified in this proposed 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

    The FAA has determined that this proposed AD would not have 
federalism implications under Executive Order 13132. This proposed AD 
would 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 the proposed 
regulation:
    (1) Is not a ``significant regulatory action'' under Executive 
Order 12866,
    (2) Would not affect intrastate aviation in Alaska, and
    (3) Would 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 Proposed Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the FAA proposes to amend 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:
0
a. Removing Airworthiness Directive (AD) 2017-23-02, Amendment 39-19096 
(82 FR 52835, November 15, 2017), and
0
b. Adding the following new AD:

The Boeing Company: Docket No. FAA-2021-0665; Project Identifier AD-
2021-00270-T.

(a) Comments Due Date

    The FAA must receive comments on this airworthiness directive 
(AD) action by October 8, 2021.

(b) Affected ADs

    This AD replaces AD 2017-23-02, Amendment 39-19096 (82 FR 52835, 
November 15, 2017) (AD 2017-23-02).

(c) Applicability

    This AD applies to The Boeing Company Model 737-100, -200, -
200C, -300, -400, and -500 series airplanes, certificated in any 
category, as identified in Boeing Alert Service Bulletin 737-
53A1358, Revision 1, dated February 26, 2021.

(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 indicating that the fuselage crown skin panels are subject to 
widespread fatigue damage. This AD was also prompted by a 
determination that certain airplane configurations and inspection 
locations need to be revised, and that additional airplanes are 
subject to the unsafe condition. The FAA is issuing this AD to 
address cracking in the fuselage crown skin panels. Multiple 
adjacent cracks in the fuselage crown skin could link up and lead to 
decompression or loss of structural integrity of the airplane.

(f) Compliance

    Comply with this AD within the compliance times specified, 
unless already done.

(g) Actions for Group 43 Airplanes

    For airplanes identified as Group 43 in Boeing Alert Service 
Bulletin 737-53A1358, Revision 1, dated February 26, 2021, within 
120 days after the effective date of this AD, inspect the airplane 
and do all applicable on-condition actions using a method approved 
in accordance with the procedures specified in paragraph (j) of this 
AD

(h) Required Actions for Groups 1 Through 42 Airplanes

    For airplanes identified as Groups 1 through 42 in Boeing Alert 
Service Bulletin 737-53A1358, Revision 1, dated February 26, 2021, 
except as specified by paragraph (i) of this AD: At the applicable 
times specified in paragraph 1.E., ``Compliance,'' of Boeing Alert 
Service Bulletin 737-53A1358, Revision 1, dated February 26, 2021, 
do all applicable actions identified as ``RC'' (required for 
compliance) in, and in accordance with, the Accomplishment 
Instructions of Boeing Alert Service Bulletin 737-53A1358, Revision 
1, dated February 26, 2021. Actions identified as terminating action 
in Boeing Alert Service Bulletin 737-53A1358, Revision 1, dated 
February 26, 2021, terminate the applicable required actions of this 
AD, provided the terminating action is done in accordance with the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1358, Revision 1, dated February 26, 2021.

(i) Exceptions to Service Information Specifications

    (1) Where Boeing Alert Service Bulletin 737-53A1358, Revision 1, 
dated February 26, 2021, uses the phrase ``the original issue date 
of this service bulletin,'' this AD requires using ``December 20, 
2017'' (the effective date of AD 2017-23-02).
    (2) Where Boeing Alert Service Bulletin 737-53A1358, Revision 1, 
dated February 26, 2021, specifies contacting Boeing for repair 
instructions or for work instructions, this AD requires doing the 
repair, or doing the work instructions and applicable on-condition 
actions using a method approved in accordance with the procedures 
specified in paragraph (j) of this AD.
    (3) Part 7 of Boeing Alert Service Bulletin 737-53A1358, 
Revision 1, dated February 26, 2021, specifies post-modification 
airworthiness limitation inspections in compliance with 14 CFR 
25.571(a)(3) at the modified locations to support compliance with 14 
CFR 121.1109(c)(2) or 129.109(b)(2). Although Part 7 is identified 
as RC, this AD does not require accomplishment of Part 7. As 
airworthiness limitations, these inspections are required by 
maintenance and operational rules. It is, therefore, unnecessary to 
mandate them in this AD. Deviations from these inspections require 
FAA approval, but do not require an alternative method of 
compliance.

[[Page 47264]]

(j) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, Los Angeles ACO 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 Related Information. Information may be emailed 
to: 9-ANM-LAACO-AMOC-Requests@faa.gov.
    (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, Los 
Angeles ACO 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) AMOCs approved for AD 2017-23-02 are approved as AMOCs for 
the corresponding provisions of Boeing Alert Service Bulletin 737-
53A1358, Revision 1, dated February 26, 2021, that are required by 
paragraph (h) of this AD.
    (5) Except as specified by paragraph (i)(2) of this AD: For 
service information that contains steps that are labeled as Required 
for Compliance (RC), the provisions of paragraphs (j)(5)(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 deviations 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, including substeps and identified figures, can still be done 
as specified, and the airplane can be put back in an airworthy 
condition.

(k) Related Information

    (1) For more information about this AD, contact James Guo, 
Aerospace Engineer, Airframe Section, FAA, Los Angeles ACO Branch, 
3960 Paramount Boulevard, Lakewood, CA 90712-4137; phone: 562-627-
5357; fax: 562-627-5210; email: james.guo@faa.gov.
    (2) 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 https://www.myboeingfleet.com. You may view this referenced 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.

    Issued on August 7, 2021.
Gaetano A. Sciortino,
Deputy Director for Strategic Initiatives, Compliance & Airworthiness 
Division,Aircraft Certification Service.
[FR Doc. 2021-18068 Filed 8-23-21; 8:45 am]
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