DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2019-0705; Product Identifier 2019-NM-098-AD; Amendment
39-21396; AD 2021-02-13]
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
certain The Boeing Company Model 737-600, -700, -700C, -800, and -900
series airplanes. This AD was prompted by reports of cracks in the bear
strap from station (STA) 290 to STA 296, and between stringers S-8R and
S-9R, sometimes common to fasteners in the gap cover and emanating from
rough sanding marks found on the surface of the bear strap. This AD
requires inspections of the fuselage skin and bear strap at the forward
galley door between certain stations for cracks, and applicable on-
condition actions. The FAA is issuing this AD to address the unsafe
condition on these products.

DATES: This AD is effective March 30, 2021.

The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of March 30, 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; phone: 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 on
the internet at https://www.regulations.gov by searching for and
locating Docket No. FAA-2019-0705.

Examining the AD Docket

You may examine the AD docket on the internet at https://www.regulations.gov
by searching for and locating Docket No. FAA-2019-
0705; 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: Michael Bumbaugh, Aerospace Engineer,
Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des
Moines, WA 98198; phone and fax: 206-231-3522; email:
michael.bumbaugh@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14
CFR part 39 by adding an AD that would apply to certain The Boeing
Company Model 737-600, -700, -700C, -800, and -900 series airplanes.
The NPRM published in the Federal Register on October 1, 2019 (84 FR
52047). The NPRM was prompted by reports of cracks in the bear strap
between certain stations, sometimes common to fasteners in the gap
cover and emanating from rough sanding marks found on the surface of
the bear strap. The NPRM proposed to require inspections of the
fuselage skin and bear strap at the forward galley door between certain
stations for cracks, and applicable on-condition actions.

The FAA issued a supplemental NPRM (SNPRM) to amend 14 CFR part 39
by adding an AD that would apply to certain The Boeing Company Model
737-600, -700, -700C, -800, and -900 series airplanes. The SNPRM
published in the Federal Register on May 1, 2020 (85 FR 25348). The FAA
issued the SNPRM to revise certain inspections to provide the correct
thickness callouts for the fuselage skin and bear strap.

The FAA is issuing this AD to address cracking of the bear strap,
which could result in severing of the bear strap, possibly leading to
uncontrolled decompression and loss of structural integrity of the
airplane.

Comments

The FAA gave the public the opportunity to participate in
developing this final rule. The following presents the comments
received on the SNPRM and the FAA's response to each comment.

Support for the SNPRM

United Airlines stated that it has no technical objection to the
SNPRM and that it concurs with the proposed rulemaking.

Request for an Alternative Method of Compliance for a Certain Repair

Southwest Airlines (SWA) requested that the Boeing 737-700/-800
Structural Repair Manual (SRM) 53-10-01, Repair 6, be approved as an
alternative method of compliance (AMOC) to certain corrective actions
specified in Boeing Alert Requirements Bulletin 737-53A1383 RB,
Revision 1, dated February 19, 2020. SWA contended that this repair
covers the affected inspection zone, and that this SRM repair should be
a terminating action to the inspections specified in Boeing Alert
Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19,
2020, because the entire inspection area covered is common to the
repair given in Boeing 737-700/-800 SRM 53-10-01, Repair 6. SWA
asserted that operators should be able to accomplish this SRM repair
without contacting Boeing, provided there are no deviations and that
the findings meet the criteria listed in the Boeing 737-700/-800 SRM
53-10-01, Repair 6. SWA also noted that the SRM was published after
Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated
February 19, 2020, so there was no way to reference the SRM repair
within it.

The FAA disagrees with the request because the referenced SRM
repair has not yet been approved for the specified conditions. However,
under the provisions of paragraph (j) of this AD, the FAA will consider
requests for approval of an AMOC if a proposal is submitted that is
supported by technical data indicating that the proposed repair will
provide an acceptable level of safety. If the referenced SRM repair is
determined to be acceptable to address the specified conditions, the
FAA may approve, and Boeing may issue, a global AMOC for the SRM
repair. The FAA has not changed this AD as a result of this comment.

Request for an Altered Compliance Time for Condition 1, Action 1, of
the Service Information

Southwest Airlines requested that where table 1 of paragraph 1.E.,
"Compliance," of Boeing Alert Requirements Bulletin 737-53A1383 RB,
Revision 1, dated February 19, 2020, states a compliance time of
"Before further flight" for certain on-condition actions, the
proposed AD should specify this compliance time as "Before 15,000
total flight cycles or within 6,000 flight cycles after the original
issue of the AD, whichever occurs later." Southwest Airlines also
requested that the FAA clarify the requirement of Condition 1, Action
1, and Condition 3 and Condition 4.1.1, within Boeing Alert
Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19,
2020, paragraph 1.E., "Compliance," in Tables 1 and 2, to do the
alternative inspections and applicable on-condition action(s) before
further flight. SWA asserted that there is an equivalent level of
safety between an airplane without a repair reaching the compliance
time threshold to perform the Boeing service bulletin inspection and an
airplane with a repair reaching the compliance time threshold before an
action is required. Therefore, the compliance times for obtaining the
alternative inspection(s) for the existing repairs should align with
the compliance times allowed for
the initial service bulletin general visual inspection in lieu of
"before further flight." SWA proposed that this allowance be listed
within paragraph (h) of the proposed AD, similar to the allowance
provided by paragraph (i) of the proposed AD.

The FAA agrees that allowing the AD compliance time for an airplane
with an existing repair to be the same as an aircraft without an
existing repair will provide an acceptable level of safety. Any
alternative inspection program including compliance times must be done
in accordance with an approved AMOC. The FAA has added paragraph (h)(3)
of this AD to address this change.

Request To Clarify Authority for Approval of Alternative Inspection Programs

Southwest Airlines requested that the FAA clarify who has the
authority to approve an alternative inspection program for any repair
found during Boeing Alert Requirements Bulletin 737-53A1383 RB,
Revision 1, dated February 19, 2020, paragraph 1.E, "Compliance,"
Table 1, Condition 1, Action 1. Paragraph (j)(1) of the proposed AD
clearly indicated that the manager of the Seattle ACO Branch has that
authority; paragraph (j)(3) of the proposed AD provided the path to
obtain an AMOC by The Boeing Company Organization Designation
Authorization (ODA) as delegated only for a repair, modification, and
alteration. SWA requested clarification whether paragraph (j)(3) of the
proposed AD encompasses both existing repairs and repairs installed as
a result of inspection findings. SWA asserted that it is unclear
whether the reference to the repair is for an existing repair that is
located in the inspection area or for a repair that is installed as a
result of any crack finding.

The FAA agrees to clarify. The Boeing Company ODA has authority to
approve AMOCs as authorized and delegated for repairs installed prior
to the AD and repairs due to a crack finding, as well as repairs not
due to a crack finding. An operator would need to provide The Boeing
Company ODA with all details and geometry needed to design and analyze
the repair data.

Request To Clarify the Use of "Covers" in the Service Information

SWA commented that Boeing Alert Requirements Bulletin 737-53A1383
RB, Revision 1, dated February 19, 2020, paragraph 1.E.,
"Compliance," Table 1, note (b), omits the inspection in areas where
a repair covers the affected zone, provided conditions 1 and 2 are met.
A similar note is included in paragraph 1.E., "Compliance," Table 2,
note (c). SWA would like clarification of the word "covers" as it
relates to repairs in the area. Since the configuration has changed
because of the repair, SWA stated that the repair's damage tolerance
program provides an equivalent level of safety for this area.

The FAA has coordinated with Boeing to clarify the intent of the
wording in this section. Note (b) in Table 1 and note (c) in Table 2 of
Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated
February 19, 2020, paragraph 1.E., "Compliance," apply to the area
"covered by" a repair, but not for the area "common to" a repair. A
repair that is "common to" the area, meaning physically in the same
area as the NPRM-proposed repair, but that was not meant to address the
issue specified in the NPRM (i.e., "covered" areas), could
potentially be obscuring the inspections that would detect crack growth
which this AD is meant to mitigate. Therefore, if a repair was not done
as a corrective action for a crack in the bear strap, and the operator
does not perform the inspections specified in the Boeing Alert
Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19,
2020, it may result in the unsafe condition. The FAA has not changed
this AD as a result of this comment.

Request To Include Inspection Programs

SWA commented that paragraph (j)(3) of the proposed AD (in the
SNPRM) stated that an AMOC may be used for any required repair,
modification, or alteration if approved by The Boeing Company ODA. SWA
stated that inspection programs should be included in this list of
conditions for which The Boeing Company ODA can provide an AMOC, as
paragraph (h)(2) explicitly states it is acceptable to accomplish
alternative inspections approved in accordance with the procedures
specified in paragraph (j) of the proposed AD.

The FAA agrees with the assertion that the inspection program may
be part of the AMOC because the inspection program for the repaired
area may be part of the repair, which in turn is part of the AMOC.
However, the FAA disagrees with changing this AD because an AMOC issued
for a repair will include the inspection program. The request to add
certain inspection programs to The Boeing Company ODA-authorized list
of AMOC approvals is outside the scope of this rulemaking. Therefore,
the FAA has not changed this AD in this regard.

Conclusion

The FAA reviewed the relevant data, considered the comments
received, and determined that air safety and the public interest
require adopting this final rule with the change described previously
and minor editorial changes. The FAA has determined that these minor
changes:

Are consistent with the intent that was proposed in the
SNPRM for addressing the unsafe condition; and

Do not add any additional burden upon the public than was
already proposed in the SNPRM.

The FAA also determined that these changes will not increase the
economic burden on any operator or increase the scope of this final rule.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Boeing Alert Requirements Bulletin 737-53A1383 RB,
Revision 1, dated February 19, 2020. This service information describes
procedures for inspecting for cracks of the fuselage skin and bear
strap at the forward galley door between certain stations, through the
use of two alternative inspection methods for the initial inspections:
(1) Internal and external general visual inspections and internal
surface high frequency eddy current (HFEC) inspections, and (2)
external general visual and external eddy current inspections. This
service information also describes procedures for applicable on-
condition actions including inspections for cracks, HFEC inspections
for cracks, low frequency eddy current (LFEC) inspections for cracks,
and repair, depending on the inspection method selected. 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 752 airplanes of U.S.
registry. The FAA estimates the following costs to comply with this AD:

Estimated Costs for Required Actions: Option 1

Estimated Costs for Required Actions: Option 2

The FAA has received no definitive data that would enable the
agency to provide cost estimates for the 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.

Adoption of 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 adding the following new airworthiness
directive: