[Federal Register Volume 86, Number 161 (Tuesday, August 24, 2021)]
[Proposed Rules]
[Pages 47255-47258]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-18069]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2021-0609; Project Identifier AD-2021-00274-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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[[Page 47256]]

SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD) 
for certain The Boeing Company Model 737-300, -400, and -500 series 
airplanes. This proposed AD was prompted by an evaluation by the design 
approval holder (DAH) indicating that the frame splice between certain 
stringers is subject to widespread fatigue damage (WFD). This proposed 
AD would require an inspection of certain fuselage frame splices for 
existing repairs, repetitive inspections of certain fuselage frame 
splices for cracking, and applicable on-condition actions. 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 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. It is also available on the internet at https://www.regulations.gov by searching for and locating Docket No. FAA-2021-
0609.

Examining the AD Docket

    You may examine the AD docket at https://www.regulations.gov by 
searching for and locating Docket No. FAA-2021-0609; 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: Wayne Ha, Aerospace Engineer, Airframe 
Section, FAA, Los Angeles ACO Branch, 3960 Paramount Boulevard, 
Lakewood, CA 90712-4137; phone: 562-627-5238; fax: 562-627-5210; email: 
wayne.ha@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-2021-0609; Project Identifier 
AD-2021-00274-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 
this 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 NPRM.

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 Wayne 
Ha, Aerospace Engineer, Airframe Section, FAA, Los Angeles ACO Branch, 
3960 Paramount Boulevard, Lakewood, CA 90712-4137; phone: 562-627-5238; 
fax: 562-627-5210; email: wayne.ha@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 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. 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),

[[Page 47257]]

while providing operators with certainty regarding the LOV applicable 
to their airplanes.
    The FAA has received a report indicating that cracking is occurring 
in the frame splice doubler and may occur in the upper frame at the 
upper frame splice between stringer S-13 and S-14 on Boeing Model 737-
300, -400, and -500 airplanes at multiple frame locations. The doubler 
cracking and possible upper frame cracking at the frame splice between 
stringer S-13 and S-14 are the result of fatigue, caused by combined 
cyclic loading from fuselage pressurization and flight loads. The FAA 
is issuing this AD to address upper frame cracking common to the frame 
splice between stringer S-13 and S-14, which could interact with 
stringer S-14 skin lap splice lower fastener row cracking in lower 
skin, and result in an uncontrolled decompression of the airplane and 
loss of structural integrity.

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 Requirements Bulletin 737-53A1388 RB, 
dated October 27, 2020. This service information specifies procedures 
for a general visual inspection (GVI) of the fuselage frame splices 
between stringer S-13 and S-14 station (STA) 360 to STA 520 and STA 
727A to STA 907 for existing repairs, repetitive inspections of the 
fuselage frame splices between stringer S-13 and S-14 from STA 360 to 
STA 520 and STA 727A to STA 907 for cracking, and applicable on-
condition actions. On-condition actions include an open hole high 
frequency eddy current (HFEC) inspection for cracking at all fastener 
hole locations where a fastener was removed due to finding a cracked 
doubler, repair, or replacement.
    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.

Proposed AD Requirements in This NPRM

    This proposed AD would require accomplishing the actions specified 
in the service information already described 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-2021-0609.

Costs of Compliance

    The FAA estimates that this AD, if adopted as proposed, would 
affect 66 airplanes of U.S. registry. The FAA estimates the following 
costs to comply with this proposed AD:

                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                                                 Cost on U.S.
             Action                     Labor cost          Parts cost     Cost per product        operators
----------------------------------------------------------------------------------------------------------------
Repetitive Inspections.........  Up to 267 work-hours x               $0  Up to $22,695 per   Up to $1,497,870
                                  $85 per hour = Up to                     inspection cycle.   per inspection
                                  $22,695 inspection                                           cycle.
                                  cycle.
GVI............................  2 work-hours x $85 per                0  $170..............  $11,220.
                                  hour = $170.
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    The FAA has received no definitive data on which to base the cost 
estimates for the on-condition actions 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 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 this 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 adding the following new airworthiness 
directive:

The Boeing Company: Docket No. FAA-2021-0609; Project Identifier AD-
2021-00274-T.

(a) Comments Due Date

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

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to The Boeing Company Model 737-300, -400, and -
500 series

[[Page 47258]]

airplanes, certificated in any category, as identified in Boeing 
Alert Requirements Bulletin 737-53A1388 RB, dated October 27, 2020.

(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 that the frame splice between stringer S-13 
and S-14 is subject to widespread fatigue damage (WFD). The FAA is 
issuing this AD to address upper frame cracking common to the frame 
splice between stringer S-13 and S-14, which could interact with 
stringer S-14 skin lap splice lower fastener row cracking in lower 
skin and result in an uncontrolled decompression of the airplane and 
loss of structural integrity.

(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 
Alert Requirements Bulletin 737-53A1388 RB, dated October 27, 2020, 
do all applicable actions identified in, and in accordance with, the 
Accomplishment Instructions of Boeing Alert Requirements Bulletin 
737-53A1388 RB, dated October 27, 2020.

    Note 1 to paragraph (g):  Guidance for accomplishing the actions 
required by this AD can be found in Boeing Alert Service Bulletin 
737-53A1388, dated October 27, 2020, which is referred to in Boeing 
Alert Requirements Bulletin 737-53A1388 RB, dated October 27, 2020.

(h) Exceptions to Service Information Specifications

    (1) Where Boeing Alert Requirements Bulletin 737-53A1388 RB, 
dated October 27, 2020, uses the phrase ``the Original Issue date of 
Requirements Bulletin 737-53A1388 RB,'' this AD requires using ``the 
effective date of this AD,'' except where Alert Requirements 
Bulletin 737-53A1388 RB, dated October 27, 2020, uses the phrase 
``the Original Issue date of Requirements Bulletin 737-53A1388 RB,'' 
in a note or flag note.
    (2) Where Boeing Alert Requirements Bulletin 737-53A1388 RB, 
dated October 27, 2020, 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.

(i) 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.

(j) Related Information

    (1) For more information about this AD, contact Wayne Ha, 
Aerospace Engineer, Airframe Section, FAA, Los Angeles ACO Branch, 
3960 Paramount Boulevard, Lakewood, CA 90712-4137; phone: 562-627-
5238; fax: 562-627-5210; email: wayne.ha@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 July 26, 2021.
Lance T. Gant,
Director, Compliance & Airworthiness Division, Aircraft Certification 
Service.
[FR Doc. 2021-18069 Filed 8-23-21; 8:45 am]
BILLING CODE 4910-13-P


