Airworthiness Directives; The Boeing Company Airplanes

DEPARTMENT OF TRANSPORTATION <SUBAGY>Federal Aviation Administration</SUBAGY> <CFR>14 CFR Part 39</CFR> <DEPDOC>[Docket No. FAA-2025-2546; Project Identifier AD-2025-01060-T]</DEPDOC> <RIN>RIN 2120-AA64</RIN> <SUBJECT>Airworthiness Directives; The Boeing Company Airplanes</SUBJECT> <HD SOURCE="HED">AGENCY:</HD> Federal Aviation Administration (FAA), DOT. <HD SOURCE="HED">ACTION:</HD> Notice of proposed rulemaking (NPRM). <SUM> <HD SOURCE="HED">SUMMARY:</HD> The FAA proposes to supersede Airworthiness Directive (AD) 2024-19-14, which applies to certain The Boeing Company Model 777-200, 777-200LR, 777-300, 777-300ER, and 777F series airplanes. AD 2024-19-14 requires repetitive inspections and bond resistance measurement of the bonding jumpers on the first fuel feed tube installed immediately forward of the wing front spar at the left and right main fuel tank penetrations, and applicable corrective actions. Since the FAA issued AD 2024-19-14, the FAA determined that additional inspections are required to address the unsafe condition. This proposed AD would require repetitive detailed inspections (DET), repetitive bond resistance measurement, and applicable on-condition actions. This proposed AD would also expand the applicability and require revising the existing maintenance or inspection program, as applicable, to incorporate a certain airworthiness limitation. The FAA is proposing this AD to address the unsafe condition on these products. </SUM> <EFFDATE> <HD SOURCE="HED">DATES:</HD> The FAA must receive comments on this proposed AD by October 30, 2025. </EFFDATE> <HD SOURCE="HED">ADDRESSES:</HD> You may send comments, using the procedures found in 14 CFR 11.43 and 11.45, by any of the following methods: • <E T="03">Federal eRulemaking Portal:</E> Go to <E T="03">regulations.gov</E> . Follow the instructions for submitting comments. • <E T="03">Fax:</E> 202-493-2251. • <E T="03">Mail:</E> U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590. • <E T="03">Hand Delivery:</E> Deliver to Mail address above between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. <E T="03">AD Docket:</E> You may examine the AD docket at <E T="03">regulations.gov</E> under Docket No. FAA-2025-2546; 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. <E T="03">Material Incorporated by Reference:</E> • 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 <E T="03">myboeingfleet.com.</E> • 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 <E T="03">regulations.gov</E> under Docket No. FAA-2025-2546. <FURINF> <HD SOURCE="HED">FOR FURTHER INFORMATION CONTACT:</HD> Samuel Dorsey, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206-231-3415; email: <E T="03">samuel.j.dorsey@faa.gov.</E> </FURINF> <SUPLINF> <HD SOURCE="HED">SUPPLEMENTARY INFORMATION:</HD> <HD SOURCE="HD1">Comments Invited</HD> 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 <E T="02">ADDRESSES</E> section. Include “Docket No. FAA-2025-2546; Project Identifier AD-2025-01060-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 <E T="03">regulations.gov</E> , including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this NPRM. <HD SOURCE="HD1">Confidential Business Information</HD> 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 Samuel Dorsey, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206-231-3415; email: <E T="03">samuel.j.dorsey@faa.gov.</E> Any commentary that the FAA receives that is not specifically designated as CBI will be placed in the public docket for this rulemaking. <HD SOURCE="HD1">Background</HD> The FAA issued AD 2024-19-14, Amendment 39-22856 (89 FR 80077, October 2, 2024) (AD 2024-19-14), for certain The Boeing Company Model 777-200, 777-200LR, 777-300, 777-300ER, and 777F series airplanes. AD 2024-19-14 was prompted by a report of potential latent failures of the lightning protection features for the engine fuel feed system. AD 2024-19-14 requires repetitive inspections and bond resistance measurement of the bonding jumpers on the first fuel feed tube installed immediately forward of the wing front spar at the left and right main fuel tank penetrations, and applicable corrective actions. The agency issued AD 2024-19-14 to address such latent failures. As discussed in the preamble to AD 2024-19-14, the electrical bonding of the engine fuel feed tube penetrating the fuel tanks of Boeing Model 777 airplanes and other Boeing airplane models is the primary design feature to prevent the development of an ignition source inside the fuel tank during a lightning strike to the engine nacelle. The electrical protective features include the spar bulkhead fitting bond that redirects the majority of current during a lightning event. Separate bonding jumpers outside and inside the fuel tank provide additional electrical paths for current from lightning strikes. Poor electrical bonding of the spar bulkhead fitting and bonding jumpers has been reported on Model 747 and Model 777 airplanes. In related rulemaking, the FAA issued AD 2023-23-14, Amendment 39-22616 (88 FR 83494, November 30, 2023) (AD 2023-23-14), to address this unsafe condition on Model 747 airplanes. An additional non-electrical feature, an encapsulation seal over the side of the spar bulkhead fitting inside the fuel tank, provides additional protection from sparking at that location. The bulkhead fitting's encapsulation is designed to isolate any sparks or arcing generated at the bulkhead fitting during a lightning strike because of failed electrical bonds from flammable fuel vapors in the tank. This fitting, including the in-tank coupler connecting the fuel feed tube to the fitting, is the most probable location for sparking when electrical bonding is poor. Therefore, a failed encapsulation significantly increases the risk of a fuel tank explosion following a lightning strike to the engine nacelle on an airplane with poor electrical bonding. Analysis has shown that at least a subset of the encapsulation failures seen on Model 747 airplanes is expected on Model 777 airplanes. The observed encapsulation failures are frequently associated with inadequate application of the encapsulation sealant. While failures are partly attributable to the design of the fitting and its associated coupler, sealant is frequently applied too thinly, does not cover the entire fitting and coupler, does not extend sufficiently onto the fuel feed tube, or the relevant surfaces are inadequately cleaned prior to application, preventing proper sealant adhesion. The bulkhead fitting encapsulation is a unique sealant task. Most sealing tasks focus on fluid-tightness or other environmental protection between joined pieces of structure. The lightning protection function and complex shape of the bulkhead fitting encapsulation installation render it difficult to apply sealant properly using general sealing instructions. The manufacturer has communicated that it intends to publish an improved set of maintenance instructions in the Aircraft Maintenance Manual (AMM) to improve the consistency of encapsulation application. The sealant application instructions in the service information required by this proposed AD, as well as the revised Critical Design Configuration Control Limitation (CDCCL) specified in this proposed AD, are detailed and should be given special attention by maintenance personnel to ensure proper application of the bulkhead fitting encapsulation. <HD SOURCE="HD1">Actions Since AD 2024-19-14 Was Issued</HD> Since the FAA issued AD 2024-19-14, the FAA determined that 777-300 Model airplanes, as well as airplanes equipped with Pratt and Whitney engines or Rolls-Royce engines, are also subject to the unsafe condition. As discussed in the Background section of the preamble to AD 2024-19-14, Model 777 series airplanes po ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 32k characters. Full document text is stored and available for version comparison. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━