Airworthiness Directives; The Boeing Company Airplanes

<RULE> DEPARTMENT OF TRANSPORTATION <SUBAGY>Federal Aviation Administration</SUBAGY> <CFR>14 CFR Part 39</CFR> <DEPDOC>[Docket No. FAA-2024-0028; Project Identifier AD-2023-00919-T; Amendment 39-23004; AD 2025-07-03]</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> Final rule. <SUM> <HD SOURCE="HED">SUMMARY:</HD> The FAA is superseding Airworthiness Directive (AD) 2021-09-06, which applied to all The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes. AD 2021-09-06 required repetitive inspections for cracking of the left- and right-hand outboard chords of certain frame fittings and failsafe straps at a certain station around eight fasteners, and repair if any cracking is found. This AD was prompted by additional reports of cracking in the area and a subsequent determination that additional inspections are needed to address the unsafe condition. This AD requires repetitive detailed and ultrasonic inspections for cracking of the left- and right-hand sides of certain frame fittings and failsafe straps, and repair if any cracking is found. The FAA is issuing this AD to address the unsafe condition on these products. </SUM> <EFFDATE> <HD SOURCE="HED">DATES:</HD> This AD is effective May 13, 2025. The Director of the Federal Register approved the incorporation by reference of a certain publication listed in this AD as of May 13, 2025. </EFFDATE> <HD SOURCE="HED">ADDRESSES:</HD> <E T="03">AD Docket:</E> You may examine the AD docket at <E T="03">regulations.gov</E> under Docket No. FAA-2024-0028; 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 final rule, any comments received, and other information. The address for Docket Operations is 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">Material Incorporated by Reference:</E> • For Boeing material identified in this AD, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; <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-2024-0028. <FURINF> <HD SOURCE="HED">FOR FURTHER INFORMATION CONTACT:</HD> Owen Bley-Male, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; telephone 206-231-3992; email <E T="03">owen.f.bley-male@faa.gov</E> . </FURINF> <SUPLINF> <HD SOURCE="HED">SUPPLEMENTARY INFORMATION:</HD> <HD SOURCE="HD1">Background</HD> The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to supersede AD 2021-09-06, Amendment 39-21519 (86 FR 23595, May 4, 2021) (AD 2021-09-06). AD 2021-09-06 applied to all The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes. The NPRM published in the <E T="04">Federal Register</E> on January 16, 2024 (89 FR 2515). The NPRM was prompted by additional reports of cracking in the area required to be inspected by AD 2021-09-06 and a subsequent determination that additional inspections are needed to address the unsafe condition. In the NPRM, the FAA proposed to require repetitive detailed and ultrasonic inspections for cracking of the left- and right-hand sides of certain frame fittings and failsafe straps, and repair if any cracking is found. The FAA is issuing this AD to address cracking in the station (STA) 663.75 frame fitting outboard chords and failsafe straps adjacent to the stringer S-18A straps, which could result in failure of a principal structural element (PSE) to sustain limit load. The unsafe condition, if not addressed, could adversely affect the structural integrity of the airplane and result in loss of control of the airplane. <HD SOURCE="HD1">Discussion of Final Airworthiness Directive</HD> <HD SOURCE="HD1">Comments</HD> The FAA received comments from four commenters, including Air Line Pilots Association, International (ALPA), Boeing, and two individuals, who supported the NPRM without change. The FAA received additional comments from five commenters, including American Airlines (American), Aviation Partners Boeing (APB), Southwest Airlines (Southwest), Sun Country Airlines (Sun Country), and United Airlines (United). The following presents the comments received on the NPRM and the FAA's response to each comment. <HD SOURCE="HD1">Effect of Winglets on Accomplishment of the Proposed Actions</HD> APB stated that the installation of blended or split scimitar winglets per Supplemental Type Certificate (STC) ST00830SE does not affect the actions specified in the proposed AD. The FAA concurs with the commenter. The FAA has redesignated paragraph (c) of the proposed AD as paragraph (c)(1) of this AD and added paragraph (c)(2) to this AD to state that installation of STC ST00830SE does not affect the ability to accomplish the actions required by this AD. Therefore, for airplanes on which STC ST00830SE is installed, a “change in product” alternative method of compliance (AMOC) approval request is not necessary to comply with the requirements of 14 CFR 39.17. <HD SOURCE="HD1">Effect of Winglets on AMOC Approval Process</HD> APB advised that AMOCs approved by the Boeing Organization Designation Authorization (ODA) in accordance with the process specified in paragraph (i)(3) of the proposed AD would not be valid for airplanes on which STC ST01697SE is installed and which have a split scimitar winglet configuration installed by STC ST00830SE. The FAA acknowledges and concurs with APB's assertion. However, paragraph (i)(1) of this AD provides a provision for obtaining an AMOC without using a Boeing ODA. An AMOC approval in accordance with paragraph (i)(1) or (3) of this AD could be provided based on whether the actions needing an AMOC apply to the APB design or the Boeing design. No change to this AD is necessary in this regard. <HD SOURCE="HD1">Request To Add Provision To Accept Certain Previously Approved AMOCs</HD> American, Southwest, Sun Country, and United requested similar changes to the proposed AD to provide credit for accomplishing replacements of the left- and right-side STA 663.75 frame fitting assembly by accepting previously approved AMOCs. American, Southwest, Sun Country, and United noted that they have replaced several cracked fittings using a method approved by FAA Form 8100-9 or the AMOC process for ADs 2021-09-06; 2019-22-10, Amendment 39-19789 (84 FR 61533, November 13, 2019) (AD 2019-22-10); and 2019-20-02, Amendment 39-19755 (84 FR 52754, October 3, 2019) (AD 2019-20-02). In addition to a request to accept AMOCs previously approved for ADs 2021-09-06, 2019-22-10, and 2019-20-02, Southwest requested acceptance of global AMOC letter 782-22-10680 for an extension of certain inspection thresholds required by AD 2021-09-06. Southwest and United stated that the repair instructions they used specified a 30,000-flight-cycle compliance time before the next inspection and requested clarification on how that compliance time in the approved repair fits with flagnote (b) in the tables of the “Compliance” paragraph and Accomplishment Instructions of Boeing Service Bulletin 737-53A1414, Revision 1, dated November 20, 2023. Sun Country also expressed concern that flagnote (b)'s reference to repairs approved by Boeing ODAs via FAA Form 8100-9 is “hidden” in the required service bulletin. The FAA agrees to allow some previously approved AMOCs for AD 2021-09-06, which includes previously approved AMOCs for AD 2019-22-10 and AD 2019-20-02, in this AD. The FAA notes that flagnote (b) in certain tables in the “Compliance” paragraph of Boeing Service Bulletin 737-53A1414, Revision 1, dated November 20, 2023, states that a replaced STA 663.75 frame fitting assembly that was accomplished using instructions approved in FAA Form 8100-9 does not need to be inspected for compliance with this AD. The FAA considers flagnote (b) to address the inspection required by this AD, but flagnote (b) does not apply to follow-on inspections specified in repair instructions. The FAA concurs with that note for the conditions that were identified by Boeing and has not excluded it or modified it in the exceptions identified in paragraph (h) of this AD. It would be impractical to attempt to identify each note or step that could be considered to contain “hidden” information that could be highlighted. The FAA has added paragraph (h)(3) of this AD to clarify that for airplanes on which the left- and right-side STA 663.75 frame fitting assembly was replaced using instructions approved via FAA Form 8100-9, the airplane is to be considered Configuration 2 of the applicable group identified in Boeing Alert Requirements Bulletin 737-53A1414 RB, Revision 1, dated November 20, 2023. The FAA has also added paragraph (i)(4) of this AD to provide acceptance for some previously approved AMOCs provided certain conditions are met. <HD SOURCE="HD1">Request for Reduced Inspection Interval Alternative to Corrective Action</HD> Sun Country requested that a reduced inspection schedule monitor be used in lieu of replacement before further flight if cracking is found on the far fasteners during the required ultrasonic inspection. Sun Country explained that based on its experience with certain inspection procedures in the non-destructive testing manual, inspecting the far fasteners as specified might lead to false cracki ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 24k characters. Full document text is stored and available for version comparison. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━