Airworthiness Directives; The Boeing Company Airplanes

DEPARTMENT OF TRANSPORTATION <SUBAGY>Federal Aviation Administration</SUBAGY> <CFR>14 CFR Part 39</CFR> <DEPDOC>[Docket No. FAA-2025-1105; Project Identifier AD-2024-00721-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) 2013-08-11, which applies to certain The Boeing Company Model 737-900 and -900ER series airplanes. AD 2013-08-11 requires repetitive inspections for cracking of the fuselage skin along chem-mill steps at certain crown skin and shear wrinkle areas and repair if necessary. Since the FAA issued AD 2013-08-11, the FAA has determined that the compliance times are not adequate. This proposed AD would continue to require the actions in AD 2013-08-11 but at reduced compliance times and would require post-modification inspections if an optional modification is accomplished. 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 July 31, 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-2025-1105; 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-2025-1105. <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-2025-1105; Project Identifier AD-2024-00721-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 issued AD 2013-08-11, Amendment 39-17428 (78 FR 24338, April 25, 2013) (AD 2013-08-11), for The Boeing Company Model 737-900 and -900ER series airplanes with certain line numbers. AD 2013-08-11 was prompted by reports of early fatigue cracks at chem-mill areas on the crown skin panels. AD 2013-08-11 requires repetitive inspections for cracking of the fuselage skin along chem-mill steps at certain crown skin and shear wrinkle areas, as applicable, and repair if necessary. AD 2013-08-11 requires the initial inspections before the airplane accumulates 43,000 total flight cycles. AD 2013-08-11 also provides modification of the inspection areas as an optional terminating action for the repetitive inspections. The agency issued AD 2013-08-11 to detect and correct fatigue cracking of the skin panel at the specified chem-mill step locations, which could result in rapid decompression of the airplane. <HD SOURCE="HD1">Actions Since AD 2013-08-11 Was Issued</HD> Since the FAA issued AD 2013-08-11, the FAA received reports of three suspected fuselage fatigue cracks found adjacent to non-chem-mill skin bays on Model 737-700 airplanes with between 40,000 and 43,000 total flight cycles—earlier than the inspection thresholds specified by AD 2013-08-11. Boeing has reported that the inspection compliance times and repetitive intervals in Boeing Service Bulletin 737-53-1312, Revision 1, dated March 14, 2012, are not adequate. The reports indicate that crack growth is faster and cracks are more distributed along the chem-mill steps between the tear straps, resulting in longer cracks than initially observed in the test data that prompted Boeing Service Bulletin 737-53-1312, Revision 1, dated March 14, 2012. As a result of these findings, the FAA has determined that reduced inspection thresholds and intervals for the chem-mill areas and the post modification inspections (for airplanes on which the optional terminating action is accomplished) are now necessary to address the unsafe condition. The FAA is considering superseding similar ADs for Model 737-600, -700, -700C, and -800 series airplanes, which have crown skin panels that are of a similar design as those on Model 737-900 and -900ER series airplanes 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 Special Attention Service Bulletin 737-53-1312, Revision 2, 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, and repairing any cracks. This material also describes procedures for installing modification doublers in certain locations, which involves an external detailed inspection and an external non-destructive (MFEC, MOI, C-Scan, or UTPA) inspection for any cracking of the area to be modified prior to the doubler being placed on that area, and a high frequency eddy current inspection of all existing holes for cracking. This material specifies that accomplishment of the modification terminates the repetitive inspections provided post-modification inspections are performed for the modified areas. 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 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-2025-1105. <HD SOURCE="HD1">Costs of Compliance</HD> The FAA estimates that this AD, if adopted as proposed, would affect 56 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="s40,r75,10,r40,r40"> <TTITLE>Estimated Costs</TTITLE> <CHED H="1">Action</CHED> <CHED H="1">Labor cost</CHED> <CHED H="1">Par ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 23k characters. Full document text is stored and available for version comparison. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━