SUPPLEMENTARY INFORMATION:

Background

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 737-8, 737-9, and 737-8200 airplanes. The NPRM was published in the Federal Register on March 23, 2026 (91 FR 13791). The NPRM was prompted by a leak through the FiP gasket at the engine fuel shutoff valve access panel found during a leak check, completed as part of a nonconformance disposition for the Boeing Company Model 737-8, 737-9, and 737-8200 airplanes. An investigation found that the fairing requirements of the engine fuel shutoff valve access panel caused thin regions of the FiP gasket, which caused the manufacturer to apply non-permitted sealant after the initial FiP gasket had cured, resulting in an uneven sealing surface on the engine fuel shutoff valve access panel and a fuel leak. In the NPRM, the FAA proposed to require a detailed inspection of the FiP gasket at the engine fuel shutoff valve access panel for correct sealant installation, or a detailed inspection at the engine fuel shutoff valve access panel for any damage on the preformed seal, depending on configuration; a fluid leak test of the engine fuel shutoff valve access panel for any leak; and applicable on-condition actions. The FAA is issuing this AD to address incorrect or missing sealant installation. The unsafe condition, if not addressed, could result in fuel leaking onto the engine exhaust nozzle and a possible fire on the ground.

Discussion of Final Airworthiness Directive

Comments

The FAA received a comment from the Air Line Pilots Association, International (ALPA) who supported the NPRM without change.

The FAA received additional comments from American Airlines (American) and Southwest Airlines (Southwest). The following presents the comments received on the NPRM and the FAA's response to each comment.

Request To Combine Proposed ADs

American requested that the FAA revise the proposed AD by incorporating the affected airplanes and proposed requirements from another proposed AD (Docket No. FAA-2026-2725, Project Identifier AD-2025-00999-T) and then rescind that other proposed AD. American noted, although the proposed ADs reference different service information and different airplane models, both proposed ADs would mandate similar corrective requirements. American stated consolidating these actions into a single NPRM would improve clarity and enhance compliance management without changing the technical intent of the inspection or impacting airplane airworthiness.

The FAA disagrees with this request. The FAA acknowledges that some operators may prefer to address the unsafe condition with a single AD; however, other operators may prefer that the FAA issue two separate ADs. Additionally, when the manufacturer develops two separate service bulletins to address an unsafe condition on different airplane models, proceeding with two separate ADs, in general, allows the FAA to address the unsafe condition on all airplane models in a timely manner. For example, if development of one service bulletin is delayed, the rulemaking process would be delayed for all affected airplane models.

Request To Remove Exceptions to Service Information Instructions

American requested that the FAA remove the exceptions in paragraphs (h)(3), (5), and (6) from the proposed AD and instead adopt the instructions in the compliance tables and appendices of Boeing Alert Requirements Bulletin 737-57A1358 RB, dated November 17, 2025 (the Boeing Alert Requirements Bulletin). American stated that the language in the service information sufficiently defines the corrective action by referencing figure 4, and that retaining this information helps maintain consistency and minimizes the potential for misinterpretation.

The FAA notes that the exceptions in paragraph (h)(3) are necessary because the “on-condition corrective action(s)” in tables 1 and 2 of the Compliance and Accomplishment Instructions of the Boeing Alert Requirements Bulletin are not defined in that bulletin. Similarly, the exceptions in paragraphs (h)(5) and (6) are necessary because Appendices A and B of the Boeing Alert Requirements Bulletin do not explicitly specify to replace the FiP gasket if the fluid leak ( printed page 67453) test fails. Therefore, the exceptions in paragraphs (h)(3), (5), and (6) are necessary to clarify what on-condition corrective actions must be taken after a fluid leak test failure. The FAA has not revised this AD in response to this comment.

Request To Clarify Post-AD Requirements

Southwest asked if the FAA agrees that, after completing the actions required by this AD, an alternative method of compliance (AMOC) is not required to maintain the airplane per the Boeing aircraft maintenance manual (AMM). Southwest stated a certain task in the Boeing AMM provides instructions that vary subtly from the procedures in the Boeing Alert Requirements Bulletin.

The FAA agrees that an AMOC is not needed to maintain the airplane after complying with the requirements of this AD if the airplane is maintained per the Boeing AMM. The FAA notes that the unsafe condition was introduced during airplane production through the application of non-permitted sealant after the initial FiP gasket had cured. Since the FAA has not received any reports of in-service events where anomalies were introduced during maintenance based on AMM instructions, the FAA considers the relevant AMM tasks to be appropriate. Further, Boeing has updated the AMM task to include notes to prevent sealant touch-up after the initial sealant application. Boeing has also updated the AMM procedures for the fluid leak test to match the procedures in the Boeing Alert Requirements Bulletin. Those updates in the AMM instructions are expected to support operators for improved maintenance of the FiP gasket or preformed seal installed at the engine fuel shutoff valve access panel.

Conclusion

The FAA reviewed the relevant data, considered any 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 on these products. Except for minor editorial changes, this AD is adopted as proposed in the NPRM. None of the changes will increase the economic burden on any operator.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Boeing Alert Requirements Bulletin 737-57A1358 RB, dated November 17, 2025. This material specifies procedures for a detailed inspection of the FiP gasket at the engine fuel shutoff valve access panel of the left and right wing for correct sealant installation, or a detailed inspection at the engine fuel shutoff valve access panel of the left and right wings for any damage on the preformed seal, depending on configuration; a fluid leak test of the engine fuel shutoff valve access panel for any leak; and applicable on-condition actions. On-condition actions include replacing the FiP gasket, repairing damage to the preformed gasket, and repeating the leak test until no leak is found.

This material 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 433 airplanes of U.S. registry. The FAA estimates the following costs to comply with this AD:

The FAA estimates the following costs to do any necessary replacements that would be required based on the results of the inspection. The agency has no way of determining the number of aircraft that might need these replacements:

The FAA has received no definitive data on which to base the cost estimates for the on-condition repairs to the preformed gasket specified in this AD.

The FAA has included all known costs in its 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 ( printed page 67454) 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.

The Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR Part 39 as follows: