AD 2022-18-13

This AD is effective October 31, 2022.

The Director of the Federal Register approved the incorporation by reference of a certain publication listed in this AD as of October 31, 2022.

AD Docket: You may examine the AD docket at regulations.gov under Docket No. FAA-2022-0093; 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.

Material Incorporated by Reference:

• For service information identified in this final rule, 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; internet myboeingfleet.com.

• You may view this service information 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 regulations.gov under Docket No. FAA-2022-0093.

Bill Ashforth, Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-231-3520; email: bill.ashforth@faa.gov.

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to certain The Boeing Company Model 737-600, -700, -700C, -800, and -900 series airplanes. The NPRM published in the Federal Register on February 25, 2022 (87 FR 10755). The NPRM was prompted by an evaluation by the DAH indicating that certain web lap splices in the center dome apex of the aft pressure bulkhead are subject to WFD. In the NPRM, the FAA proposed to require a general visual inspection for existing repairs at the aft pressure bulkhead; repetitive detailed, HFEC, and LFEC inspections; and repair if necessary. The FAA is issuing this AD to address fatigue cracks in the webs of the aft pressure bulkhead, which could result in reduced structural integrity of the airplane.

The FAA received comments from United Airlines and two individuals, who supported the NPRM without change.

The FAA received additional comments from Southwest Airlines (SWA), Boeing, and Aviation Partners Boeing. The following presents the comments received on the NPRM and the FAA's response to each comment.

Aviation Partners Boeing stated that accomplishing 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.

Boeing requested that the FAA revise the SUMMARY of the NPRM and paragraph (e) of the proposed AD. Boeing noted that the SUMMARY of the NPRM and paragraph (e) of the proposed AD refer to WFD, but Boeing contends that the unsafe condition was caused by pull up on the first two fasteners at the web lap splices in the center dome apex. Boeing explained that these fasteners, which are located adjacent to the area where the aft web transitions over the forward web in the lap splice, are subject to clamp-up stresses (which are pre-stresses during the assembly). These stresses, combined with pressurization, will reduce the fatigue life of the web at the center dome apex and potentially cause early cracking in this location.

The FAA partially agrees. The FAA agrees with Boeing that the unsafe condition was discovered through clamp-up stresses, as well as other non-WFD events. The WFD evaluation revealed that the area is susceptible to WFD; as a result, this unsafe condition is related to WFD. Therefore, the FAA maintains that the SUMMARY of this final rule and paragraph (e) of this AD are correct in stating that the affected areas are subject to WFD. The FAA has not changed this AD in this regard.

SWA requested clarification regarding paragraph (h)(2) of the proposed AD. SWA noted that in Table 1 of paragraph 3., Compliance, of Boeing Alert Requirements Bulletin 737-53A1403 RB, dated August 26, 2021, CONDITION 1 (ACTION 1) specifies to contact Boeing for any repair found during the general visual inspection of the aft pressure bulkhead. CONDITION 1 (ACTION 1) also references flag note (a), which states:

CONDITION 1 (ACTION 1) is not required for any repair found during the General Visual Inspection of the APB [aft pressure bulkhead] aft side in areas where a repair covers the affected inspection zones provided that the installed repair was approved by The Boeing Company Organization Designation Authorization (ODA) via a FAA Form 8100-9 and inspections are accomplished in accordance with the scheduled repair approval listed on the FAA Form 8100-9.

SWA stated that its interpretation is that paragraph (h)(2) of the proposed AD applies to all repairs found where the operator must contact Boeing due to the repair not meeting the criteria listed in flag note (a). SWA went on to observe that if the repairs found during CONDITION 1 (ACTION 1) meet the requirements of flag note (a), then the operator is not required to contact Boeing.

The FAA provides the following clarification. SWA is correct in its interpretation that paragraph (h)(2) of this AD applies to all instances where the operator must contact Boeing for repair instructions or for alternative inspections. If the repairs found during the general visual inspection of the aft pressure bulkhead aft side meet the requirements of flag note (a) of Table 1 of paragraph 3., Compliance, of Boeing Alert Requirements Bulletin 737-53A1403 RB, dated August 26, 2021, then contacting Boeing is not required. The FAA has not changed this AD in this regard.

The FAA reviewed the relevant data, considered any comments received, and determined that air safety requires adopting this AD as proposed. Except for minor editorial changes, and any other changes described previously, this AD is adopted as proposed in the NPRM. None of the changes will increase the economic burden on any operator.

The FAA reviewed Boeing Alert Requirements Bulletin 737-53A1403 RB, dated August 26, 2021. This service information specifies procedures for a general visual inspection for existing repairs at the aft pressure bulkhead; repetitive detailed, HFEC, and LFEC inspections for any crack; and repair of cracks if necessary. This service information is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in ADDRESSES.

The FAA estimates that this AD affects 1,187 airplanes of U.S. registry. The FAA estimates the following costs to comply with this AD:

The FAA has received no definitive data on which to base the cost estimates for the on-condition repairs specified in this AD.

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII: Aviation Programs, describes in more detail the scope of the Agency's authority.

The FAA is issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701: General requirements. Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

This AD will not have federalism implications under Executive Order 13132. This AD will not have a substantial direct effect on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government.

For the reasons discussed above, I certify that this AD:

(1) Is not a “significant regulatory action” under Executive Order 12866,

(2) Will not affect intrastate aviation in Alaska, and

(3) Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

Accordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows:

1. The authority citation for part 39 continues to read as follows:

2. The FAA amends § 39.13 by adding the following new airworthiness directive: