    [Federal Register Volume 91, Number 58 (Thursday, March 26, 2026)]
    [Proposed Rules]
    [Pages 14654-14657]
    From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
    [FR Doc No: 2026-05843]

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    DEPARTMENT OF TRANSPORTATION

    Federal Aviation Administration

    14 CFR Part 39

    [Docket No. FAA-2026-2725; Project Identifier AD-2025-00999-T]
    RIN 2120-AA64

    Airworthiness Directives; The Boeing Company Airplanes

    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

    [[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

    [[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:

                                                     Estimated Costs
    ----------------------------------------------------------------------------------------------------------------
                                                                                         Cost per      Cost on U.S.
                    Action                         Labor cost           Parts cost        product        operators
    ----------------------------------------------------------------------------------------------------------------
    Inspection............................  1 work-hour x $85 per                 $0             $85         $87,550
                                             hour = $85.
    Leak test.............................  1 work-hour x $85 per                  0              85          87,550
                                             hour = $85.
    ----------------------------------------------------------------------------------------------------------------

        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:

                                                   On-Condition Costs
    ----------------------------------------------------------------------------------------------------------------
                                                                                                         Cost per
                     Action                           Labor cost                  Parts cost              product
    ----------------------------------------------------------------------------------------------------------------
    Replacement.............................  2 work-hours x $85 per      Negligible................            $170
                                               hour = $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

    0
    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]

    0
    2. The FAA amends Sec.  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

    [[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]
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