Discussion \n\n\n\tThe 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 October 1, 2019 (84 FR 52047). The NPRM was prompted by reports of cracks in the bear strap between certain stations, sometimes common to fasteners in the gap cover and emanating from rough sanding marks found on the surface of the bear strap. The NPRM proposed to require inspections of the fuselage skin and bear strap at the forward galley door between certain stations for cracks, and applicable on-condition actions. \n\tThe FAA issued a supplemental NPRM (SNPRM) 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 SNPRM published in the Federal Register on May 1, 2020 (85 FR 25348). The FAA issued the SNPRM to revise certain inspections to provide the correct thickness callouts for the fuselage skin and bear strap. \n\tThe FAA is issuing this AD to address cracking of the bear strap, which could result in severing of the bear strap, possibly leading to uncontrolled decompression and loss of structural integrity of the airplane. \n\nComments \n\n\n\tThe FAA gave the public the opportunity to participate in developing this final rule. The following presents the comments received on the SNPRM and the FAA's response to each comment. \n\nSupport for the SNPRM \n\n\n\tUnited Airlines stated that it has no technical objection to the SNPRM and that it concurs with the proposed rulemaking. \n\nRequest for an Alternative Method of Compliance for a Certain Repair \n\n\n\tSouthwest Airlines (SWA) requested that the Boeing 737-700/-800 Structural Repair Manual (SRM) 53-10-01, Repair 6, be approved as an alternative method of compliance (AMOC) to certain corrective actions specified in Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020. SWA contended that this repair covers the affected inspection zone, and that this SRM repair should be a terminating action to the inspections specified in Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, because the entire inspection area covered is common to the repair given in Boeing 737-700/-800 SRM 53-10-01, Repair 6. SWA asserted that operators should be able to accomplish this SRM repair without contacting Boeing, provided there are no deviations and that the findings meet the criteria listed in the Boeing 737-700/-800 SRM 53-10-01, Repair 6. SWA also noted that the SRM was published after Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, so there was no way to reference the SRM repair within it. \n\tThe FAA disagrees with the request because the referenced SRM repair has not yet been approved for the specified conditions. However, under the provisions of paragraph (j) of this AD, the FAA will consider requests for approval of an AMOC if a proposal is submitted that is supported by technical data indicating that the proposed repair will provide an acceptable level of safety. If the referenced SRM repair is determined to be acceptable to address the specified conditions, the FAA may approve, and Boeing may issue, a global AMOC for the SRM repair. The FAA has not changed this AD as a result of this comment. \n\nRequest for an Altered Compliance Time for Condition 1, Action 1, of the Service Information \n\n\n\tSouthwest Airlines requested that where table 1 of paragraph 1.E., ''Compliance,'' of Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, states a compliance time of ''Before further flight'' for certain on-condition actions, the proposed AD should specify this compliance time as ''Before 15,000 total flight cycles or within 6,000 flight cycles after the original issue of the AD, whichever occurs later.'' Southwest Airlines also requested that the FAA clarify the requirement of Condition 1, Action 1, and Condition 3 and Condition 4.1.1, within Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, paragraph 1.E., ''Compliance,'' in Tables 1 and 2, to do the alternative inspections and applicable on-condition action(s) before further flight. SWA asserted that there is an equivalent level of safety between an airplane without a repair reaching the compliance time threshold to perform the Boeing service bulletin inspection and an airplane with a repair reaching the compliance time threshold before an action is required. Therefore, the compliance times for obtaining the alternative inspection(s) for the existing repairs should align with the compliance times allowed for \n\n((Page 10778)) \n\nthe initial service bulletin general visual inspection in lieu of ''before further flight.'' SWA proposed that this allowance belisted within paragraph (h) of the proposed AD, similar to the allowance provided by paragraph (i) of the proposed AD. \n\tThe FAA agrees that allowing the AD compliance time for an airplane with an existing repair to be the same as an aircraft without an existing repair will provide an acceptable level of safety. Any alternative inspection program including compliance times must be done in accordance with an approved AMOC. The FAA has added paragraph (h)(3) of this AD to address this change. \n\nRequest To Clarify Authority for Approval of Alternative Inspection Programs \n\n\n\tSouthwest Airlines requested that the FAA clarify who has the authority to approve an alternative inspection program for any repair found during Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, paragraph 1.E, ''Compliance,'' Table 1, Condition 1, Action 1. Paragraph (j)(1) of the proposed AD clearly indicated that the manager of the Seattle ACO Branch has that authority; paragraph (j)(3) of the proposed AD provided the path to obtain an AMOC by The Boeing Company Organization Designation Authorization (ODA) as delegated only for a repair, modification, and alteration. SWA requested clarification whether paragraph (j)(3) of the proposed AD encompasses both existing repairs and repairs installed as a result of inspection findings. SWA asserted that it is unclear whether the reference to the repair is for an existing repair that is located in the inspection area or for a repair that is installed as a result of any crack finding. \n\tThe FAA agrees to clarify. The Boeing Company ODA has authority to approve AMOCs as authorized and delegated for repairs installed prior to the AD and repairs due to a crack finding, as well as repairs not due to a crack finding. An operator would need to provide The Boeing Company ODA with all details and geometry needed to design and analyze the repair data. \n\nRequest To Clarify the Use of ''Covers'' in the Service Information \n\n\n\tSWA commented that Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, paragraph 1.E., ''Compliance,'' Table 1, note (b), omits the inspection in areas where a repair covers the affected zone, provided conditions 1 and 2 are met. A similar note is included in paragraph 1.E., ''Compliance,'' Table 2, note (c). SWA would like clarification of the word ''covers'' as it relates to repairs in the area. Since the configuration has changed because of the repair, SWA stated that the repair's damage tolerance program provides an equivalent level of safety for this area. \n\tThe FAA has coordinated with Boeing to clarify the intent of the wording in this section. Note (b) in Table 1 and note (c) in Table 2 of Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, paragraph 1.E., ''Compliance,'' apply to the area ''covered by'' a repair, but not for the area ''common to'' a repair. A repair that is ''common to'' the area, meaning physically in the same area as the NPRM-proposed repair, but that was not meant to address the issue specified in the NPRM (i.e., ''covered'' areas), could potentially be obscuring the inspections that would detect crack growth which this AD is meant to mitigate. Therefore, if a repair was not done as a corrective action for a crack in the bear strap, and the operator does not perform the inspections specified in the Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, it may result in the unsafe condition. The FAA has not changed this AD as a result of this comment. \n\nRequest To Include Inspection Programs \n\n\n\tSWA commented that paragraph (j)(3) of the proposed AD (in the SNPRM) stated that an AMOC may be used for any required repair, modification, or alteration if approved by The Boeing Company ODA. SWA stated that inspection programs should be included in this list of conditions for which The Boeing Company ODA can provide an AMOC, as paragraph (h)(2) explicitly states it is acceptable to accomplish alternative inspections approved in accordance with the procedures specified in paragraph (j) of the proposed AD. \n\tThe FAA agrees with the assertion that the inspection program may be part of the AMOC because the inspection program for the repaired area may be part of the repair, which in turn is part of the AMOC. However, the FAA disagrees with changing this AD because an AMOC issued for a repair will include the inspection program. The request to add certain inspection programs to The Boeing Company ODA-authorized list of AMOC approvals is outside the scope of this rulemaking. Therefore, the FAA has not changed this AD in this regard. \n\nConclusion \n\n\n\tThe FAA reviewed the relevant data, considered the comments received, and determined that air safety and the public interest require adopting this final rule with the change described previously and minor editorial changes. The FAA has determined that these minorchanges: \n\tAre consistent with the intent that was proposed in the SNPRM for addressing the unsafe condition; and \n\tDo not add any additional burden upon the public than was already proposed in the SNPRM. \n\tThe FAA also determined that these changes will not increase the economic burden on any operator or increase the scope of this final rule. \n\nRelated Service Information Under 1 CFR Part 51 \n\n\n\tThe FAA reviewed Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020. This service information describes procedures for inspecting for cracks of the fuselage skin and bear strap at the forward galley door between certain stations, through the use of two alternative inspection methods for the initial inspections: (1) Internal and external general visual inspections and internal surface high frequency eddy current (HFEC) inspections, and (2) external general visual and external eddy current inspections. This service information also describes procedures for applicable on- condition actions including inspections for cracks, HFEC inspections for cracks, low frequency eddy current (LFEC) inspections for cracks, and repair, depending on the inspection method selected. 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 the ADDRESSES section. \n\nCosts of Compliance \n\n\n\tThe FAA estimates that this AD affects 752 airplanes of U.S. registry. The FAA estimates the following costs to comply with this AD: \n\n((Page 10779)) \n\n\n\n\n\n\n\tEstimated Costs for Required Actions: Option 1 ---------------------------------------------------------------------------------------------------------------- \n\tCost on U.S. \n\tAction Labor cost Parts cost Cost per product operators ---------------------------------------------------------------------------------------------------------------- Internalgeneral visual 11 work-hours x $85 $0 $935............... $703,120. \n\tinspection. per hour = $935. External general visual 1 work-hour x $85 0 85................. 63,920. \n\tinspection. per hour = $85. Internal Surface HFEC inspections 3 work-hours x $85 0 255 per inspection 191,760 per \n\tper hour = $255 cycle. inspection cycle. \n\tper inspection \n\tcycle. ---------------------------------------------------------------------------------------------------------------- \n\n\n\n\n\tEstimated Costs for Required Actions: Option 2 ---------------------------------------------------------------------------------------------------------------- \n\tCost on U.S. \n\tAction Labor cost Parts cost Cost per product operators ---------------------------------------------------------------------------------------------------------------- External general visual 1 work-hour x $85 $0 $85................ $63,920. \n\tinspection. per hour = $85. External LFEC and HFEC 18 work-hours x $85 0 1,530 per 1,150,560 per \n\tinspections. per hour = $1,530 inspection cycle. inspection cycle. \n\tper inspection \n\tcycle. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tThe FAA has received no definitive data that would enable the agency to provide cost estimates for the on-condition actions specified in this AD. \n\nAuthority for This Rulemaking \n\n\n\tTitle 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. \n\tThe 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. \n\nRegulatory Findings \n\n\n\tThis 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. \n\tFor the reasons discussed above, I certify that this AD: \n\t(1) Is not a ''significant regulatory action'' under Executive Order 12866, \n\t(2) Will not affect intrastate aviation in Alaska, and \n\t(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. \n\nList of Subjects in 14 CFR Part 39 \n\n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.