2026-13129: Airworthiness Directives; The Boeing Company Airplanes

Federal Register, Volume 91 Issue 124 (Tuesday, June 30, 2026) [Federal Register Volume 91, Number 124 (Tuesday, June 30, 2026)] [Proposed Rules] [Pages 39573-39575] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 2026-13129] ----------------------------------------------------------------------- DEPARTMENT OF TRANSPORTATION Federal Aviation Administration 14 CFR Part 39 [Docket No. FAA-2026-4668; Project Identifier AD-2025-01680-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) for certain The Boeing Company Model 747-400 series airplanes. This proposed AD was prompted by reports of potable water leaking into the electrical equipment bay cooling air inlet. This proposed AD would require performing repetitive inspections of potential water sources from the upper deck and the main deck, including potable water and waste water lines, for any water leaks and clogs, 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 August 14, 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-2026-4668; 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-2026-4668.

For Further Information Contact

Nicole S. Tsang, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206- 231-3959; email: [email protected].

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-2026-4668; Project Identifier AD-2025-01680-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 Nicole S. Tsang, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206-231-3959; email: [email protected]. 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 received reports of potable water leaking into the electrical equipment bay cooling air inlet on the Boeing Model 777F series airplanes. There are no reported events of water leaking into the electrical equipment bay cooling air inlet on the large cargo freighter variant of the Model 747-400 series airplanes. However, there are reported events of leakages on the upper deck in areas that could pool and drip onto the air inlet. The FAA has determined that the large cargo freighter variant has unique design features that introduce several potential potable and waste water sources from the upper deck and the main deck that could leak into the air inlet and enter the electrical equipment bay. This condition, if not addressed, could impact the function of multiple electronics and line replaceable units in the equipment bay racks that are essential for safe flight, which could result in loss of continued safe flight and landing. 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 Message TBC-TBC-25-6694-01B, dated [[Page 39574]] November 7, 2025 (pages 4 through 15 of this document are dated October 29, 2025). This material specifies procedures for the following repetitive inspections of potential water sources from the upper deck and the main deck, including potable water and waste water lines, for any water leaks and clogs, and applicable on-condition actions. The inspections include the following actions: Perform general visual inspection (GVI) of the potable water lines for any water leaks; Run the coffee maker through a brew cycle; Perform GVI of the galley compartments for any water leaks; Check for any indication of clog from the drainage system in the lavatory and galley sinks and the lavatory and galley sink drains; Perform GVI of the floor of the lavatory, the lavatory sink, the area behind the galley on its outboard left side including the potable water and waste water lines, and the upper deck hallway floor for signs of leakage; and Inspect the potable water and drain lines running along the main deck ceiling for sign of leaks. On-condition actions include using normal operator procedures and repeating the work step(s) as required to resolve the leakage or clog or rendering the water/waste systems or individual components inoperable; and checking the engine indication crew alert system (EICAS) display for any new messages. 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 identified as ``RC'' (required for compliance) in the Water Leak Check Work Instructions of Boeing Message TBC-TBC-25-6694-01B, dated November 7, 2025, 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 material at regulations.gov under Docket No. FAA-2026-4668. Clarification of Compliance Time for On-Condition Actions Although Boeing Message TBC-TBC-25-6694-01B, dated November 7, 2025, specifies the compliance time to perform RC actions is within 1,000 flight hours (FH) of the date of Boeing Message TBC-TBC-25-6694- 01B and at recurring intervals not to exceed 1,000 FH, step 27 of the Water Leak Check Work Instructions specifies the compliance times for the applicable on-condition actions are before further flight. Therefore, paragraph (h)(2) of this proposed AD would require the applicable on-condition actions to be done before further flight. Interim Action The FAA considers that this proposed AD would be an interim action. The manufacturer is currently developing a modification that will address the unsafe condition identified in this AD. Once this modification is developed, approved, and available, the FAA might consider additional rulemaking. Costs of Compliance The FAA estimates that this AD, if adopted as proposed, would affect 4 airplanes of U.S. registry. The FAA estimates the following costs to comply with this proposed AD: Estimated Costs ---------------------------------------------------------------------------------------------------------------- Cost on U.S. Action Labor cost Parts cost Cost per product operators ---------------------------------------------------------------------------------------------------------------- Inspection....................... 5 work-hours x $85 $0 $425 per inspection $1,700 per per hour = $425 cycle. inspection cycle. per inspection cycle. ---------------------------------------------------------------------------------------------------------------- The FAA estimates the following costs to do any necessary on- condition actions 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 on-condition actions: On-Condition Costs ---------------------------------------------------------------------------------------------------------------- Action Labor cost Parts cost Cost per product ---------------------------------------------------------------------------------------------------------------- On-condition actions.................... Up to 6 work-hours x $85 $0 Up to $510. per hour = $510. ---------------------------------------------------------------------------------------------------------------- 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. [[Page 39575]] 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