DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2024-1880; Project Identifier AD-2023-01149-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 all The Boeing Company Model 737-600, -700, -700C, -800, -900, and
-900ER series airplanes. This proposed AD was prompted by a report of a
frame web crack at fuselage station (STA) 328 between stringers S-20R
and S-21R common to the frame web notch. This proposed AD would require
repetitive detailed inspections of the forward and aft sides of the
frames and high frequency eddy current (HFEC) inspections of the frames
for cracks and repairing any crack found. 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 August 16,
2024.

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 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.
AD Docket: You may examine the AD docket at regulations.gov under
Docket No. FAA-2024-1880; 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.
Material Incorporated by Reference:
For service information, 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; website myboeingfleet.com.
You may view this service information at the FAA,
Airworthiness Products Section, Operational Safety Branch, 2200 South
216th Street, Des Moines, WA. For information on the availability of
this material at the FAA, call 206-231-3195. It is also available at
regulations.gov under Docket No. FAA-2024-1880.

FOR FURTHER INFORMATION CONTACT: Bill Ashforth, Aviation Safety
Engineer, FAA, 2200 South 216th Street, Des Moines, WA 98198; phone:
206-231-3520; email: bill.ashforth@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-2024-1880; Project Identifier
AD-2023-01149-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
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 Bill
Ashforth, Aviation Safety Engineer, FAA, 2200 South 216th Street, Des
Moines, WA 98198; phone: 206-231-3520; email: bill.ashforth@faa.gov.
Any commentary that the FAA receives that is not specifically
designated as CBI will be placed in the public docket for this
rulemaking.

Background

The FAA has received a report that an operator of a Model 737-700
airplane found a frame web crack at fuselage STA 328 between stringers
S-20R and S-21R while performing a visual inspection of the electrical
and electronics compartment during scheduled maintenance. The crack was
common to the frame web notch and was approximately 0.85 inch long. The
crack originated at a notch radius of the lower frame web that is
subject to a load transfer from the inner chord of the upper frame.
Because the load transfer is similar in adjacent areas, the frames at
STA 312, STA 328, and STA 344 from stringers S-20R to S-23R are also
affected. Model 737-600, -700C, -800, -900, and -900ER series airplanes
have similar structure in the affected area and are also subject to
this unsafe condition. Undetected cracks in the frame could lead to the
inability of the principal structural element to sustain limit loads,
which could result in the subsequent loss of 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 737-53A1410 RB,
dated October 11, 2023. This service information specifies procedures
for repetitive detailed inspections of the forward and aft sides of the
frames, and surface and open hole HFEC inspections of the frames, at
STA 312 from S-20R to S-23R, STA 328 from S-19R to S-22R, and STA 344
from S-20R to S-23R for cracks. This service information also specifies
repairing any crack found.
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 regulations.gov under Docket No. FAA-
2024-1880.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would
affect 1,583 airplanes of U.S. registry. The FAA estimates the
following costs to comply with this proposed AD:

Estimated Costs

Estimated Costs of On-Condition Actions

The extent of damage/cracking found during the proposed inspections
could vary significantly from airplane to airplane. The FAA has no way
of determining the type of repair or cost to repair any cracks on each
airplane or the number of airplanes that may require repair.

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

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: