Airworthiness Directives; The Boeing Company Airplanes

DEPARTMENT OF TRANSPORTATION <SUBAGY>Federal Aviation Administration</SUBAGY> <CFR>14 CFR Part 39</CFR> <DEPDOC>[Docket No. FAA-2025-3429; Project Identifier AD-2024-00722-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) 2017-19-26, which applies to certain The Boeing Company Model 737-600, -700, -700C, -800, and -900 series airplanes. AD 2017-19-26 requires repetitive inspections for cracks along the chem-milled steps of the fuselage skin and missing or loose fasteners in the area of the preventive modification or repairs; replacement of the time-limited repair with a permanent repair, if applicable; and applicable corrective actions that end certain repetitive inspections. AD 2017-19-26 also requires repetitive inspections for modified airplanes. Since the FAA issued AD 2017-19-26, the FAA has determined that the compliance times are not adequate. This proposed AD would continue to require certain actions in AD 2017-19-26 but at reduced compliance times. This proposed AD would also revise instructions for the preventative modification and remove instructions for the permanent and time-limited repairs. 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 January 2, 2026. </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-2025-3429; 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 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-2025-3429. <FURINF> <HD SOURCE="HED">FOR FURTHER INFORMATION CONTACT:</HD> Luis Cortez-Muniz, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206-231-3958; email: <E T="03">luis.a.cortez-muniz@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-2025-3429; Project Identifier AD-2024-00722-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 the 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 proposed AD. <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 Luis Cortez-Muniz, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206-231-3958; email: <E T="03">luis.a.cortez-muniz@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 2017-19-26, Amendment 39-19056 (82 FR 44504, September 25, 2017) (AD 2017-19-26), for The Boeing Company Model 737-600, -700, -700C, -800, and -900 series airplanes with certain line numbers. AD 2017-19-26 was prompted by a fatigue test that revealed numerous cracks in the upper skin panel at the chem-milled step above the lap joint, followed by an evaluation by the design approval holder (DAH) that indicated that the upper skin panel at the chem-milled step above the lap joint is subject to widespread fatigue damage (WFD) if the preventative modification was installed after 30,000 total flight cycles. AD 2017-19-26 requires repetitive inspections for cracks along the chem-milled steps of the fuselage skin and missing or loose fasteners in the area of the preventive modification or repairs; replacement of the time-limited repair with a permanent repair, if applicable; and applicable corrective actions which would end certain repetitive inspections. AD 2017-19-26 also requires repetitive inspections for modified airplanes. The FAA issued AD 2017-19-26 to detect and correct cracking of the upper skin panel at the chem-milled step above the lap joint, which could result in reduced structural integrity of the airplane. <HD SOURCE="HD1">Actions Since AD 2017-19-26 Was Issued</HD> Since the FAA issued AD 2017-19-26, the FAA received reports of five chemically milled skin cracks in an area just above the S-4 lap joint on airplanes with 38,000 and 53,000 total flight cycles. One of the cracks was found before the airplane reached the next repeat interval specified in Boeing Alert Service Bulletin 737-53A1232, Revision 3, dated July 27, 2015. As a result of these findings, the FAA has determined that reduced inspection intervals for the chem-mill areas and post-modification inspections (for airplanes on which the optional preventative modification is accomplished), as well as revised instructions for the preventative modification and removal of the instructions for the permanent and time-limited repairs, are now necessary to address the unsafe condition. In addition, the FAA has determined that the end-level effect for the unsafe condition is rapid decompression of the airplane. The FAA has revised this NPRM accordingly. The FAA is considering superseding similar ADs for Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes common to different locations, which have crown skin panels that are of a similar design as those on Model 737-600, -700, -700C, -800, and -900 series airplanes addressed by this proposed AD and may be subject to the same unsafe condition. <HD SOURCE="HD1">FAA's Determination</HD> 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. <HD SOURCE="HD1">Material Incorporated by Reference Under 1 CFR Part 51</HD> The FAA reviewed Boeing Alert Service Bulletin 737-53A1232, Revision 4, dated May 22, 2024. This material specifies procedures for repetitive external detailed inspections and either (1) external medium frequency eddy current (MFEC), magneto optic imager (MOI), or C-scan inspections or (2) external ultrasonic phased array (UTPA) inspections for cracks in the fuselage skin at chem-milled steps and pockets at certain locations, and repairing any cracks, as well as repetitive post-permanent repair inspections, and post-time-limited repair inspections. This material specifies that accomplishment of the preventative modification terminates the repetitive inspections. The preventative modification includes an external eddy current inspection of the skin and fastener holes for any crack and installation of a doubler. 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 <E T="02">ADDRESSES</E> section. <HD SOURCE="HD1">Proposed AD Requirements in This NPRM</HD> This proposed AD would require accomplishing the actions specified in the material already described, except for any differences identified as exceptions in the regulatory text ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 28k characters. Full document text is stored and available for version comparison. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━