DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2020-0459; Product Identifier 2020-NM-049-AD; Amendment
39-21380; AD 2021-01-04]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for all
The Boeing Company Model 737 series airplanes, excluding Model 737-100,
-200, -200C, -300, -400, and -500 series airplanes. This AD was
prompted by reports of cracked or completely severed lugs in the upper
aft corner stop fitting assembly of the forward entry door. This AD
requires an inspection, a measurement, or a records check of that
assembly to determine the part number, and replacement if a certain
part is found. The FAA is issuing this AD to address the unsafe
condition on these products.

DATES: This AD is effective March 29, 2021.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of March 29,
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 on
the internet at https://www.regulations.gov by searching for and
locating Docket No. FAA-2020-0459.

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-2020-
0459; 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 all The Boeing Company
Model 737 series airplanes, excluding Model 737-100, -200, -200C, -300,
-400, and -500 series airplanes. The NPRM published in the Federal
Register on June 3, 2020 (85 FR 34136). The NPRM was prompted by
reports of cracked or completely severed lugs in the upper aft corner
stop fitting assembly of the forward entry door. Analysis of the design
of the stop fitting assembly revealed that undersized wall thickness of
the lug made it susceptible to fatigue cracking, which may result in
the forward entry door being unable to sustain limit load. In the NPRM,
the FAA proposed to require an inspection, a measurement, or a records
check of that assembly to determine the part number, and replacement if
a certain part-numbered assembly is installed.
The FAA is issuing this AD to address cracked or completely severed
lugs, which could result in reduced structural integrity of the forward
entry door and consequent rapid decompression of the airplane.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from four commenters. The following
presents the comments received on the NPRM and the FAA's response to
each comment.

Effect of Winglets on Accomplishment of the Proposed Actions

Aviation Partners Boeing stated that the installation of winglets
per Supplemental Type Certificate (STC) ST00830SE does not affect
compliance with the proposed actions.
The FAA agrees that the installation of winglets per STC ST00830SE
would not affect the ability to replace the affected stop fitting
assembly with a newly designed stop fitting assembly as 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) accordingly.

Request for Compliance Actions at the Component Level

Southwest Airlines (SWA) asked that the compliance actions be
reported at the component level due to the interchangeability of the
forward entry doors between the Model 737 NG and 737 MAX fleets.
The FAA infers that the commenter is requesting that the AD's
applicability point towards the component parts, rather than the
airplane. The FAA acknowledges that the component most likely to be
rotated is the forward entry door because doors are likely removed with
the stop fittings intact. However, the FAA disagrees with changing the
applicability of this AD because the unsafe condition is related to the
stop fitting assembly and an affected stop fitting assembly may be
installed on a forward entry door of any airplane identified in
paragraph (c) of this AD. In addition, paragraph (i) of this AD,
``Parts Installation Prohibition,'' states that no person may install a
forward entry door that has a stop fitting assembly with part number
(P/N) 141A6104-3 on any airplane. The FAA used this language because
doors are often rotated among aircraft with the stop fitting assembly
already installed. The FAA has therefore determined that an airplane-
level applicability is appropriate and has not changed this AD in this
regard.

Request for Clarification of Compliance Time

SWA asked for clarification of the reference in paragraph (g) of
the proposed AD to the applicable times specified in the ``Compliance''
paragraph of Boeing Alert Requirements Bulletin 737-52A1180 RB, dated
January 24, 2020. SWA asked if once it is determined that a P/N
141A6104-3 fitting is installed on a door through records or survey,
the fitting must be replaced before further flight or whether it can be
replaced at a later date as long as the door is still within its
required compliance time per the referenced service information.
``Table 1: Forward Entry Door Number 7 Stop Fitting Assembly
Inspection'' of Paragraph 3., ``Compliance'' of Boeing Service Bulletin
737-52A1180, dated January 24, 2020, gives the compliance time for
replacing the P/N 141A6104-3 fitting if found. The compliance time is
before 10,000 total flight cycles on the forward entry door, or within
5,000 forward entry door flight cycles after the original issue date of
Boeing Alert Requirements Bulletin 737-52A1180 RB, dated January 24,
2020, whichever occurs later. However, under paragraph (h) of this AD,
the date for determining compliance time is the effective date of this
AD, and not the issue date of the bulletin. Therefore, the FAA
clarifies that if the compliance time has not yet been reached, then
the fitting does not need to be replaced before further flight. The FAA
has not changed this AD in this regard.

Request To Change Parts Installation Prohibition Paragraph

SWA asked that the FAA reword paragraph (i) of the proposed AD to
require compliance with the service information before installation of
the fitting instead of prohibiting installation of the fitting.
The intent of paragraph (i) of this AD is to prohibit installation
of an affected part on an airplane with a compliance time for this
prohibition related to the airplane configuration and whether the
actions specified in Boeing Alert Requirements Bulletin 737-52A1180 RB,
dated January 24, 2020, must be accomplished on that airplane. The FAA
has not made the changes requested by the commenter. However, the FAA
has revised paragraph (i) of this AD to clarify that, for any airplane
required to accomplish the actions required by paragraph (g) of this
AD, the parts installation prohibition does not take effect until the
applicable actions required by paragraph (g) of this AD have been
accomplished on that airplane. For airplanes having an original
airworthiness certificate or original export certificate of
airworthiness dated after the effective date of this AD, the parts
installation prohibition continues to be applicable as of the effective
date of this AD.

Request for Correction of Error in Service Information

AIRDO requested the FAA correct an error in the service information
incorporated by reference in paragraph (g) of the proposed AD. AIRDO
noted that page 13 of Boeing Alert Requirements Bulletin 737-52A1180
RB, dated January 24, 2020, refers to the procedures in ``SB 747-
52A1180'' when the correct reference is ``SB 737-52A1180.''
The FAA agrees with the commenter's request. The FAA has added
paragraph (h)(3) of this AD to clarify the correct service information
reference.

Request To Limit the Applicability

American Airlines (AA) and AIRDO requested the FAA limit the
applicability of the proposed AD to the line numbers (L/Ns) identified
in the effectivity of Boeing Alert Service Bulletin 737-52A1180, dated
January 24, 2020. AA stated that because the aircraft illustrated parts
catalog (IPC) does not allow for the unsafe part to be installed on
aircraft beyond L/N 1075, or on the door assemblies allowed to be
installed on aircraft beyond L/N 1075, including all Model 737-600, -
700, -700C, -800, -900, and -900ER series airplanes in the
applicability of the proposed AD is unnecessarily redundant. AIRDO
stated Boeing has not allowed operators to install P/Ns 141A6104-3,
141A6150-1, 141A6150-2, and 141A6100-678 on airplanes other than those
with L/N 1-1075 per the IPC and related drawings. AIRDO also stated
that if the fitting or the door assembly must be replaced, operators
will check the IPC and drawing to confirm if the affected part number
can be used on the specific airplane. AIRDO stated that based on this
general protocol, even though the fitting and door assembly are
physically interchangeable, a suspected fitting and door assembly
cannot be installed on airplanes having L/N 1076 and subsequent.
The FAA does not agree with the requests to limit the
applicability. Both the stop fitting assemblies and the doors they are
installed on are physically interchangeable among the airplane models
listed in the applicability of this AD. The FAA has determined it is
necessary to ensure these rotable parts will not be introduced on other
airplanes by including these airplanes in the applicability of this AD.
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 requires adopting this AD as
proposed. Accordingly, the FAA is issuing this AD to address the unsafe
condition in these products. Except for the 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 Requirements Bulletin 737-52A1180 RB,
dated January 24, 2020. The service information specifies procedures
for an inspection, a measurement, or a records check of the upper aft
corner stop fitting assembly to determine the part number, and
applicable on-condition actions. The on-condition action is to replace
the affected stop fitting assembly with a newly designed stop fitting
assembly that has improved wall thickness and strength. 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 1,075 airplanes of U.S.
registry. The FAA estimates the following costs to comply with this AD:

Estimated Costs for Required Actions

The FAA has included all known costs in the cost estimate.
According to the manufacturer, however, some or all of the costs of
this AD may be covered under warranty, thereby reducing the cost impact
on affected operators.

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 adding the following new airworthiness
directive: