Proposed Rule

Airworthiness Directives; The Boeing Company Airplanes

A Proposed Rule by the Federal Aviation Administration on 03/26/2026

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• Public Inspection Published Document: 2026-05843 (91 FR 14654) Document Headings ###### Department of Transportation

Federal Aviation Administration

1. 14 CFR Part 39
2. [Docket No. FAA-2026-2725; Project Identifier AD-2025-00999-T]
3. RIN 2120-AA64

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) certain The Boeing Company Model 737-700, -700C, -800, and -900ER series airplanes. This proposed AD was prompted by a leak through the form-in-place (FiP) gasket at the engine fuel shutoff valve access panel found during a leak check. This proposed AD would require a detailed inspection of the left and right side FiP gasket at the engine ( printed page 14655) fuel shutoff valve access panel, for correct sealant installation, a fluid leak test of the engine fuel shutoff valve access panels for any leak, and applicable on-condition actions. 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 May 11, 2026.

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-2026-2725; 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 Boeing material identified in this proposed AD, 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 material 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 regulations.gov under Docket No. FAA-2026-2725.

FOR FURTHER INFORMATION CONTACT:

Erica Bayles, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 907-271-5844; email: erica.e.bayles@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 using a method listed under the ADDRESSES section. Include “Docket No. FAA-2026-2725; Project Identifier AD-2025-00999-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 Erica Bayles, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 907-271-5844; email: erica.e.bayles@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 indicating a leak through the FiP gasket at the engine fuel shutoff valve access panel was found during a leak check, completed as part of a non-conformance 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. This caused the manufacturer to apply non-permitted sealant after the initial FiP gasket had cured, which resulted in an uneven sealing surface on the engine fuel shutoff valve access panel and leak. Non-conforming FiP gasket installations may compromise the designated drainage provision in the wing leading edge area. This condition, if not addressed, could result in fuel leaking onto the engine exhaust nozzle and a consequent fire on the ground.

Boeing determined that Model 737-700, -700C, -800, and -900ER series airplanes are also subject to the identified unsafe condition due to design similarity of the FiP gasket. The FAA is considering separate rulemaking for the affected Boeing Company Model 737-8, 737-9, and 737-8200 airplanes.

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.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 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 side wing for correct sealant installation, a fluid leak test of the engine fuel shutoff valve access panels for any leak, and applicable on-condition actions. On-condition actions include replacing the FiP gasket, repairing any leaks, 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.

Proposed AD Requirements in This NPRM

This proposed AD would require accomplishing the actions specified in the material already described, except as discussed under “Differences Between this Proposed AD and the Referenced Material,” and 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 material at regulations.gov under Docket No. FAA-2026-2725.

Differences Between This Proposed AD and the Referenced Material

Since Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 2025, was issued, the FAA has determined more airplanes are affected by the unsafe condition. The line numbers affected are 2438 through 2598 inclusive, 2600 through 2721 inclusive, 2723 through 2813 inclusive, 2815 through 2930 inclusive, 2932 ( printed page 14656) through 3068 inclusive, 3070 through 3323 inclusive, 3325 through 3425 inclusive, 3427 through 3521 inclusive, 3523 through 3611 inclusive, 3613 through 3701 inclusive, 3703 through 3791 inclusive, and 3793 through 3833 inclusive. The FAA has added these lines numbers to the applicability in paragraph (c) of this proposed AD.

Where Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 2025, specifies to do applicable on-condition corrective actions if any leak is found, for this proposed AD, if any leak is found the FiP gasket must be replaced. The FAA has added exceptions in paragraphs (h)(2) through (4) of this proposed AD accordingly.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect 1,030 airplanes of U.S. registry. The FAA estimates the following costs to comply with this proposed AD:

| Action | Labor cost | Parts cost | Cost per
product | Cost on U.S.
operators |
| --- | --- | --- | --- | --- |
| Inspection | 1 work-hour × $85 per hour = $85 | $0 | $85 | $87,550 |
| Leak test | 1 work-hour × $85 per hour = $85 | 0 | 85 | 87,550 |
The FAA estimates the following costs to do any necessary replacements that would be required based on the results of the proposed inspection. The agency has no way of determining the number of aircraft that might need these replacements:

| Action | Labor cost | Parts cost | Cost per
product |
| --- | --- | --- | --- |
| Replacement | 2 work-hours × $85 per hour = $170 | Negligible | $170 |
The FAA has received no definitive data on which to base the cost estimates for the on-condition repairs specified in this proposed 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 proposed 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

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.

§ 39.13 [Amended] 2. The FAA amends § 39.13 by adding the following new airworthiness directive:

The Boeing Company: Docket No. FAA-2026-2725; Project Identifier AD-2025-00999-T.

(a) Comments Due Date

The FAA must receive comments on this airworthiness directive (AD) by May 11, 2026.

(b) Affected ADs

None.

(c) Applicability

This AD applies to The Boeing Company Model 737-700, -700C, -800, and -900ER series airplanes, certificated in any category, as identified in Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 2025; and airplanes having line numbers 2438 through 2598 inclusive, 2600 through 2721 inclusive, 2723 through 2813 inclusive, 2815 through 2930 inclusive, 2932 through 3068 inclusive, 3070 through 3323 inclusive, 3325 through 3425 inclusive, 3427 through 3521 inclusive, 3523 through 3611 inclusive, 3613 through 3701 inclusive, 3703 through 3791 inclusive, and 3793 through 3833 inclusive.

(d) Subject

Air Transport Association (ATA) of America Code 57, Wings.

(e) Unsafe Condition

This AD was prompted by a leak through the form-in-place (FiP) gasket at the engine fuel shutoff valve access panel found during ( printed page 14657) a leak check. An investigation found that the fairing requirements of the engine fuel shutoff valve access panel caused thin regions of the FiP gasket, which caused non-permitted sealant to be applied after the initial FiP gasket had cured, resulting in an uneven sealing surface on the engine fuel shutoff valve access panel and leak. 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.

(f) Compliance

Comply with this AD within the compliance times specified, unless already done.

(g) Required Actions

Except as specified by paragraph (h) of this AD: At the applicable times specified in the “Compliance” paragraph of Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 2025, do all applicable actions identified in, and in accordance with, the Accomplishment Instructions of Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 2025.

Note 1 to paragraph (g): Guidance for accomplishing the actions required by this AD can be found in Boeing Alert Service Bulletin 737-57A1359, dated October 3, 2025, which is referred to in Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 2025.

(h) Exceptions to Requirements Bulletin Specifications

(1) Where the Compliance Time columns of the tables in the “Compliance” paragraph of Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 2025, refer to the original issue date of Requirements Bulletin 737-57A1359 RB, this AD requires using the effective date of this AD.

(2) Where Table 1 and Table 2 in the Compliance and Accomplishment Instructions paragraphs of Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 2025, specifies “Do a fluid leak test of the engine fuel shutoff valve access panel for any leak. If any leak is found, do all applicable on-condition corrective action(s) and repeat the leak test until no leak is found”, this AD requires replacing that text with “Do a fluid leak test of the engine fuel shutoff valve access panel for any leak. If any leak is found, replace the FiP gasket and repeat the leak test until no leak is found”.

(3) Where step 4. b. of Appendix A in Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 2025, specifies “If any water leaks from the engine fuel shutoff valve access panel in less than two minutes, the fluid leak test has failed”, this AD requires replacing that text with “If any water leaks from the engine fuel shutoff valve access panel in less than two minutes, the fluid leak test has failed. Replace the FiP gasket in accordance with Figure 3 and repeat the leak test until no leak is found”.

(4) Where step 4. b. of Appendix B in Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 2025, specifies “If any water leaks from the engine fuel shutoff valve access panel in less than two minutes, the fluid leak test has failed”, this AD requires replacing that text with “If any water leaks from the engine fuel shutoff valve access panel in less than two minutes, the fluid leak test has failed. Replace the FiP gasket in accordance with Figure 4 and repeat the leak test until no leak is found”.

(i) Alternative Methods of Compliance (AMOCs)

(1) The Manager, AIR-520, Continued Operational Safety 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 Continued Operational Safety Branch, send it to the attention of the person identified in paragraph (j) of this AD. Information may be emailed to: AMOC@faa.gov. Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the responsible Flight Standards Office.

(2) 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, AIR-520, Continued Operational Safety 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.

(j) Additional Information

For more information about this AD, contact Erica Bayles, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 907-271-5844; email: erica.e.bayles@faa.gov.

(k) Material Incorporated by Reference

(1) The Director of the Federal Register approved the incorporation by reference of the material listed in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.

(2) You must use this material as applicable to do the actions required by this AD, unless the AD specifies otherwise.

(i) Boeing Alert Requirements Bulletin 737-57A1359 RB, dated October 3, 2025.

(ii) [Reserved]

(3) For Boeing material identified in this AD, 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.

(4) You may view this material 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.

(5) You may view this material at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, visit www.archives.gov/​federal-register/​cfr/​ibr-locations or email fr.inspection@nara.gov.

Issued on March 23, 2026.

Peter A. White,

Deputy Director, Integrated Certificate Management Division, Aircraft Certification Service.

[FR Doc. 2026-05843 Filed 3-25-26; 8:45 am]

BILLING CODE 4910-13-P

Published Document: 2026-05843 (91 FR 14654)