[Federal Register Volume 87, Number 38 (Friday, February 25, 2022)]
[Proposed Rules]
[Pages 10755-10757]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-03968]



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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2022-0093; Project Identifier AD-2021-00987-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 adopt a new airworthiness directive (AD) 
for certain The Boeing Company Model 737-600, -700, -700C, -800, and -
900 series airplanes. This proposed AD was prompted by an evaluation by 
the design approval holder (DAH) indicating that certain web lap 
splices in the center dome apex of the aft pressure bulkhead are 
subject to widespread fatigue damage (WFD). This proposed AD would 
require a general visual inspection for existing repairs at the aft 
pressure bulkhead, repetitive detailed, high frequency eddy current 
(HFEC), and low frequency eddy current (LFEC) inspections, and repair 
if necessary. 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 April 11, 
2022.

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 at https://www.regulations.gov by searching for and locating Docket No. FAA-2022-
0093.

Examining the AD Docket

    You may examine the AD docket at https://www.regulations.gov by 
searching for and locating Docket No. FAA-2022-0093; 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: Dirk Visser, Aerospace Engineer, 
Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des 
Moines, WA 98198; phone and fax: 206-231-3994; email: 
[email protected].

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-2022-0093; Project Identifier 
AD-2021-00987-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 Dirk 
Visser, Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 
2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-231-
3994; email: [email protected]. 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

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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 regarding the LOV applicable to their airplanes.
    The FAA has received an evaluation by the DAH indicating that 
certain web lap splices in the center dome apex of the aft pressure 
bulkhead are subject to WFD. During cycle tests of The Boeing Company 
Model 737-800 series airplanes' Fatigue Test Article for the 0.032 inch 
web (the configuration for The Boeing Company Model 737-600, -700, -
700C, -800, and -900 series airplane having line numbers (LN) 1 through 
1166), cracks were found in three of the seven aft pressure bulkhead 
web lap splices in several of the fastener rows common to the center 
dome apex. The pull down stresses were caused by the single rivet 
located in the area where each of the webs transition up 0.032 inches. 
Airplanes having LN 1167 through 1755 inclusive have a different 
fastener pattern than airplanes having LN 1 through 1166 inclusive, but 
are subject to the same unsafe condition. There has been only one 
reported finding on airplanes having LN 1167 through 1755 inclusive and 
cracking was found in five of the seven webs. The FAA issued AD 2021-
21-09, Amendment 39-21769 (86 FR 61679, November 8, 2021) to address 
fatigue cracks in the webs of the aft pressure bulkhead on The Boeing 
Company Model 737-600, -700, -700C, -800, and -900 airplanes having LN 
1 through 1755 inclusive.
    The Boeing Company Model 737-600, -700, -700C, -800, and -900 
airplanes having LN 1756 and subsequent (which are addressed in this 
proposed AD) have a 0.040 inch web thickness. Following the findings in 
the earlier LNs, supplemental testing showed an increase in the pull 
down stress for the 0.040 inch aft pressure bulkhead configuration in 
the same transition area as seen in the 0.032 inch configuration. The 
aft pressure bulkhead web lap splice fasteners are subjected to 
fuselage pressurization fatigue cycles and additional clamp-up stress 
caused from the assembly process. The clamp up stresses, combined with 
the pressurization, cause the existing airworthiness limitations 
inspections for Principle Structural Element 53-80-01-3 (visible web 
rows) and 53-80-01-7 (hidden web rows) to be inadequate. Therefore, the 
FAA determined that additional inspections of the 0.040 inch thick web 
lap splices at station 1016 aft pressure bulkhead center dome apex for 
any crack are necessary to mitigate the identified unsafe condition. 
This condition, if not addressed, could result in reduced structural 
integrity of the airplane.

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 737-53A1403 RB, 
dated August 26, 2021. This service information specifies procedures 
for a general visual inspection for existing repairs at the aft 
pressure bulkhead, repetitive detailed, HFEC, and LFEC inspections for 
any crack, 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 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-2022-0093.

Costs of Compliance

    The FAA estimates that this AD, if adopted as proposed, would 
affect 1,187 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
----------------------------------------------------------------------------------------------------------------
Inspection for repairs.........  1 work-hour x $85  $0....................  $85..............  $100,895.
                                  per hour = $85.
Repetitive detailed, HFEC, and   Up to 9 work-      Up to $0..............  Up to $765 per     Up to $908,055
 LFEC inspections.                hours x $85 per                            inspection cycle.  per inspection
                                  hour = $765 per                                               cycle.
                                  inspection cycle.
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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 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

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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-2022-0093; Project Identifier AD-
2021-00987-T.

(a) Comments Due Date

    The FAA must receive comments on this airworthiness directive 
(AD) by April 11, 2022.

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to The Boeing Company Model 737-600, -700, -
700C, -800, and -900 series airplanes, certificated in any category, 
as identified in Boeing Alert Requirements Bulletin 737-53A1403 RB, 
dated August 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 (DAH) indicating that certain web lap splices in the center 
dome apex of the aft pressure bulkhead are subject to widespread 
fatigue damage (WFD). The FAA is issuing this AD to address fatigue 
cracks in the webs of the aft pressure bulkhead, which could result 
in reduced 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 
Alert Requirements Bulletin 737-53A1403 RB, dated August 26, 2021, 
do all applicable actions identified in, and in accordance with, the 
Accomplishment Instructions of Boeing Alert Requirements Bulletin 
737-53A1403 RB, dated August 26, 2021.
    Note 1 to paragraph (g): Guidance for accomplishing the actions 
required by this AD can be found in Boeing Alert Service Bulletin 
737-53A1403, dated August 26, 2021, which is referred to in Boeing 
Alert Requirements Bulletin 737-53A1403 RB, dated August 26, 2021.

(h) Exceptions to Service Information Specifications

    (1) Where the Compliance Time column of the table in the 
``Compliance'' paragraph of Boeing Alert Requirements Bulletin 737-
53A1403 RB, dated August 26, 2021, uses the phrase ``the original 
issue date of the Requirements Bulletin 737-53A1403 RB,'' this AD 
requires using ``the effective date of this AD.''
    (2) Where Boeing Alert Requirements Bulletin 737-53A1403 RB, 
dated August 26, 2021, 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, Seattle 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 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, Seattle 
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 Dirk Visser, 
Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 2200 
South 216th St., Des Moines, WA 98198; phone and fax: 206-231-3994; 
email: [email protected].
    (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 February 3, 2022.
Lance T. Gant,
Director, Compliance & Airworthiness Division, Aircraft Certification 
Service.
[FR Doc. 2022-03968 Filed 2-24-22; 8:45 am]
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