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2021-21-09 THE BOEING COMPANY:
Amendment 39-21769; Docket No. FAA-2021-0503; Project Identifier AD-2021-00163-T.

(a) EFFECTIVE DATE

    This airworthiness directive (AD) is effective December 13, 2021.

(b) AFFECTED ADS

    This AD replaces AD 2005-05-18, Amendment 39-14007 (70 FR 12410, March
    14, 2005) (AD 2005-05-18).

(c) APPLICABILITY

(1) 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 Service Bulletin 737-53A1251 Revision 2, dated January
    20, 2021.

(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 of cracks  found at several  of the
    fastener rows  in the  web lap  splices at  the dome  apex of  the aft
    pressure bulkhead, and the  determination that airplanes not  affected
    by AD  2005-05-18 are  subject to  this unsafe  condition. The  FAA is
    issuing this  AD to  address fatigue  cracks in  the webs  of the  aft
    pressure bulkhead, which  could result in  rapid decompression of  the
    airplane.

(f) COMPLIANCE

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

(g) REQUIRED ACTIONS

    Except as  specified by  paragraph (h)  of this  AD: At the applicable
    times  specified  in  paragraph 1.E.,  "Compliance,"  of  Boeing Alert
    Service Bulletin 737-53A1251  Revision 2, dated  January 20, 2021,  do
    all applicable  actions identified  as "RC"  (required for compliance)
    in, and in accordance with, the Accomplishment Instructions of  Boeing
    Alert  Service Bulletin  737-53A1251,  Revision  2,  dated January 20,
    2021.  For  Group 1  airplanes,  as defined  in  Boeing Alert  Service
    Bulletin 737-53A1251, Revision 2, dated January 20, 2021: Step  3.B.2.
    of the  Accomplishment Instructions  of Boeing  Alert Service Bulletin
    737-53A1251, Revision 2,  dated January 20,  2021, is an  RC step, and
    the provisions of paragraphs (j)(5)(i) and (ii) of this AD apply.

(h) EXCEPTIONS TO SERVICE INFORMATION SPECIFICATIONS

(1) Where  Boeing Alert Service Bulletin 737-53A1251,  Revision  2,  dated
    January 20, 2021, uses the phrase "the Revision 1 date of this service
    bulletin," this AD requires using "the effective date of this AD."

(2) Where  Boeing Alert Service Bulletin 737-53A1251,  Revision  2,  dated
    January 20, 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 (j) of this AD.

(i) CREDIT FOR PREVIOUS ACTIONS

(1) For airplanes having line numbers 1 through 1166 inclusive: This para-
    graph provides credit  for the corresponding  actions  of Boeing Alert
    Service Bulletin 737-53A1251, Revision 2, dated January 20, 2021, that
    are required by paragraph (g)  of this AD,  if those actions were per-
    formed before the effective date of this AD using Boeing Service Bull-
    etin 737-53-1251, dated June 3, 2004, which was incorporated by refer-
    ence in AD 2005-05-18.

(2) This paragraph provides credit for the corresponding actions of Boeing
    Alert Service Bulletin 737-53A1251 Revision 2, dated January 20, 2021,
    that are required by paragraph (g)  of this AD,  if those actions were
    performed before the effective date  of  this  AD  using  Boeing Alert
    Service Bulletin 737-53A1251,  Revision 1,  dated  September 22, 2020,
    which is not incorporated by reference in this AD.

(j) 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 (k)(1) 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
    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.

(4) AMOCs approved for AD 2005-05-18 are approved as AMOCs  for the corre-
    sponding  provisions  of  Boeing  Alert Service Bulletin  737-53A1251,
    Revision 2, dated January 20, 2021, that are required by paragraph (g)
    of this AD.

(5) 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  (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 Wayne Lockett,  Aerospace
    Engineer, Airframe Section, FAA,  Seattle ACO Branch, 2200 South 216th
    St., Des Moines, WA 98198;  phone and fax: 206-231-3524; email: wayne.
    lockett@faa.gov.

(2) Service information identified in this AD  that is not incorporated by
    reference is available at the addresses specified in paragraphs (l)(3)
    and (4) of this AD.

(l) 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 737-53A1251, Revision 2,  dated  January
    20, 2021.

(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; internet https://www.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 service information  that is incorporated  by refer-
    ence at the National  Archives and Records Administration  (NARA). For
    information  on  the  availability of  this  material  at NARA,  email
    fr.inspection@nara.gov,  or  go to:  https://www.archives.gov/federal-
    register/cfr/ibr-locations.html.

Issued on October 8, 2021. Gaetano A. Sciortino, Deputy Director for Stra-
tegic Initiatives, Compliance & Airworthiness Division,  Aircraft Certifi-
cation Service.

FOR FURTHER INFORMATION CONTACT:  Wayne Lockett,  Aerospace Engineer, Air-
frame Section, FAA, Seattle ACO Branch,  2200 South 216th St., Des Moines,
WA 98198; phone and fax: 206-231-3524; email: wayne.lockett@faa.gov.
PREAMBLE 

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2021-0503; Project Identifier AD-2021-00163-T;
Amendment 39-21769; AD 2021-21-09]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: The FAA is superseding Airworthiness Directive (AD) 2005-05-
18, which applied to certain The Boeing Company Model 737-600, -700, -
700C, -800, and -900 series airplanes. AD 2005-05-18 required
repetitive inspections for cracking of the webs of the aft pressure
bulkhead at a certain body station, and corrective action if necessary.
This AD was prompted by cracking found in that inspection area on
airplanes not identified in the applicability of AD 2005-05-18. This AD
retains the requirements of AD 2005-05-18, revises the applicability to
include additional airplanes, and adds an inspection for existing
repairs on the newly added airplanes. The FAA is issuing this AD to
address the unsafe condition on these products.

DATES: This AD is effective December 13, 2021.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of December 13,
2021.

ADDRESSES: 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; 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-2021-0503.

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2021-0503; 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.

FOR FURTHER INFORMATION CONTACT: Wayne Lockett, Aerospace Engineer,
Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des
Moines, WA 98198; phone and fax: 206-231-3524; email:
wayne.lockett@faa.gov.

SUPPLEMENTARY INFORMATION:

Background

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14
CFR part 39 to supersede AD 2005-05-18, Amendment 39-14007 (70 FR
12410, March 14, 2005) (AD 2005-05-18). AD 2005-05-18 applied to
certain The Boeing Company Model 737-600, -700, -700C, -800, and -900
series airplanes. The NPRM published in the Federal
Register on June 30, 2021 (86 FR 34660). The NPRM was prompted by
cracking found in an inspection area on airplanes not identified in the
applicability of AD 2005-05-18. In the NPRM, the FAA proposed to
continue to require repetitive inspections for cracking of the webs of
the aft pressure bulkhead at a certain body station, and corrective
action if necessary. The NPRM also proposed to require revising the
applicability to include additional airplanes, and adding an inspection
for existing repairs on the newly added airplanes. The FAA is issuing
this AD to address fatigue cracks in the webs of the aft pressure
bulkhead, which could result in rapid decompression of the airplane.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from United Airlines and Jack Kendrick,
who supported the NPRM without change.
The FAA received additional comments from two commenters, including
Boeing and Aviation Partners Boeing. The following presents the
comments received on the NPRM and the FAA's response to each comment.

Effects of Winglets on Accomplishment of the Proposed Actions


Aviation Partners Boeing stated that the installation of blended or
split scimitar winglets per Supplemental Type Certificate (STC)
ST00830SE does not affect compliance with the proposed actions.
The FAA agrees with the commenter that the installation of winglets
per STC ST00830SE does not affect the accomplishment of the
manufacturer's service instructions. Therefore, the installation of STC
ST00830SE does not affect the ability to accomplish the actions
required by this AD. Operators of airplanes with these winglets do not
need to request a ``change in product'' alternative method of
compliance (AMOC) approval as specified in 14 CFR 39.17. 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 accordingly.

Request To Clarify Service Information Description

Boeing asked that the FAA clarify the language describing the
inspection location and reporting requirements in the ``Related Service
Information Under 1 CFR 51'' paragraph in the preamble of the proposed
AD. Boeing stated that the language should identify the center dome
apex location, and also specify reporting of any cracks found.
The FAA agrees with the commenter's request to clarify the
inspection location in the ``Related Service Information'' section, due
to the vast number of web fasteners located around the bulkhead. The
FAA has clarified that language accordingly.
The FAA does not agree with the commenter's request to add
reporting language to that section, because the manufacturer did not
include a reporting requirement for this particular cracking condition
in the service information. Therefore, the FAA has not changed this AD
in this regard.

Request To Clarify Language in Actions Since AD 2005-05-18 Was Issued
Section


Boeing requested that the FAA clarify the language in the Actions
Since AD 2005-05-18 Was Issued section of the proposed AD. Boeing
suggested changing the sentence that begins ``During the assembly
process on line numbers 1167 through 1755, the fasteners,'' as follows:
``Fasteners on line numbers 1167 through 1755 in the apex dome region
are subjected to clamp-up stresses from the assembly process and
fatigue cycles during fuselage pressurization.'' Boeing stated that
this change is to clarify the meaning of the language used in the
proposed AD.
The FAA acknowledges the commenter's request and agrees the
proposed wording provides clarity. However, that section is not carried
over into this final rule. Therefore, the FAA has not changed this AD
in this regard.

Conclusion

The FAA reviewed the relevant data, considered any comments
received, and determined that air safety requires adopting this AD as
proposed. 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 737-53A1251,
Revision 2, dated January 20, 2021. This service information specifies
procedures for a general visual inspection for existing repairs,
repetitive detailed and high frequency eddy current (HFEC) inspections
for cracks around the web center dome apex fasteners, repetitive low
frequency eddy current (LFEC) inspection for cracks around the hidden
web lap splice fastener locations, and repair of cracks. 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.

Costs of Compliance

The FAA estimates that this AD affects 744 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
Detailed, HFEC, and LFEC inspections Up to 10 work-hours x $85 per hour = Up to $850 per inspection cycle $0 Up to $850 per inspection cycle Up to $632,400 per inspection cycle
General visual inspection (194 airplanes) 1 work-hour x $85 per hour = $85 0 $85 $16,490

The FAA estimates the following costs to do any necessary repairs
that are required based on the results of the inspections. The FAA has
no way of determining the number of aircraft that might need these
repairs:

On-Condition Costs

Action
Labor cost
Parts cost
Cost per product
Repair Up to 30 * work-hours x $85 per hour = Up to $2,550 Up to $30,000 * Up to $32,550.*

* Repair costs will vary depending on size of the repair required.

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:

a. Removing Airworthiness Directive (AD) 2005-05-18, Amendment 39-14007
(70 FR 12410, March 14, 2005); and

b. Adding the following new AD: