Airworthiness Directives; The Boeing Company Airplanes

DEPARTMENT OF TRANSPORTATION <SUBAGY>Federal Aviation Administration</SUBAGY> <CFR>14 CFR Part 39</CFR> <DEPDOC>[Docket No. FAA-2025-2548; Project Identifier AD-2024-00478-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 adopt a new airworthiness directive (AD) for all The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes. This proposed AD was prompted by reports of shim installations at certain stub beam to longitudinal floor beam locations that were not installed per specifications, and an evaluation by the design approval holder indicating inadequate baseline inspections for cracking of the stub beam. This proposed AD would require repetitive inspections for any crack of the stub beam straps at certain stations and repairing any crack found. 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 November 13, 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-2025-2548; 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-2025-2548. <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 to an address listed under the <E T="02">ADDRESSES</E> section. Include “Docket No. FAA-2025-2548; Project Identifier AD-2024-00478-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 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 has received reports of shim installations at the station (STA) 559 to STA 639 stub beam to buttock line (BL) 45 longitudinal floor beam locations that were not installed per specifications, and an evaluation by the design approval holder indicating inadequate baseline inspections for cracking of the stub beam. The FAA is issuing this AD to address potential cracking in the stub beam strap. The unsafe condition, if not addressed, could result in undetected cracks in the stub beam strap that may grow in length and sever the strap, which could adversely affect the structural integrity of the airplane. <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 Requirements Bulletin 737-53A1404 RB, Revision 1, dated November 29, 2023. This material specifies procedures for repetitive ultrasonic inspections for any crack of the stub beam straps at STA 578 and STA 597, or STA 578 and STA 601, as applicable. This material specifies procedures for repetitive ultrasonic and open hole eddy current inspections for any crack of the stub beam straps at STA 616 and STA 639. This material also specifies repairing any crack 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 <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 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 <E T="03">regulations.gov</E> under Docket No. FAA-2025-2548. <HD SOURCE="HD1">Differences Between This Proposed AD and the Referenced Material</HD> Boeing received reports of several crack findings from operators after accomplishment of Boeing Alert Requirements Bulletin 737-53A1404 RB, Revision 1, dated November 29, 2023. The crack findings were discovered prior to the inspection threshold of 34,000 total flight cycles, which is specified in the compliance tables in Boeing Alert Requirements Bulletin 737-53A1404 RB, Revision 1, dated November 29, 2023. Further analysis by Boeing determined that the existing compliance times in Boeing Alert Requirements Bulletin 737-53A1404 RB, Revision 1, dated November 29, 2023, are inadequate and would need to be reduced. Following coordination with Boeing, the FAA is proposing to require reduced compliance times to address the unsafe condition and maintain safety in the fleet. Additionally, Boeing Alert Requirements Bulletin 737-53A1404 RB, Revision 1, dated November 29, 2023, specifies reduced compliance times for airplanes on which Boeing Business Jet (BBJ) Lower Cabin Altitude Supplemental Type Certificate (STC) ST01697SE has been incorporated. This proposed AD would require using those reduced compliance times, but the reduction would be applied to the reduced compliance times specified in paragraphs (g)(1) through (3) of this AD, not those specified in Boeing Alert Requirements Bulletin 737-53A1404 RB, Revision 1, dated November 29, 2023. <HD SOURCE="HD1">Costs of Compliance</HD> The FAA estimates that this AD, if adopted as proposed, would affect 1,981 airplanes of U.S. registry. The FAA estimates the following costs to comply with this proposed AD: <GPOTABLE COLS="5" OPTS="L2,nj,i1" CDEF="xs72,r50,10,r50,r50"> <TTITLE>Estimated Costs</TTITLE> <CHED H="1">Action</CHED> <CHED H="1">Labor cost</CHED> <CHED H="1">Parts cost</CHED> Cost on U.S. operators </CHED> <ROW> <ENT I="01">Inspections</ENT> <ENT>Up to 166 work-hours × $85 per hour = $14,110 per inspection cycle</ENT> <ENT>$0</ENT> <ENT>Up to $14,110 per inspection cycle</ENT> <ENT>Up to $27,951,910 per inspection cycle.</ENT> </ROW> </GPOTABLE> The FAA has received no definitive data on which to base the cost estimates for the 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, ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 19k characters. 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