Discussion \n\n\n\tWe issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to all The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. The NPRM published in the Federal Register on December 6, 2018 (83 FR 62741). The NPRM was prompted by reports of cracks caused by corrosion of the edge of the bore of the spot face and corrosion of the lug bore of certain side-strut support fitting lugs. The NPRM proposed to require repetitive detailed inspections of the left and right side- strut support fitting lugs with bushings installed for any corrosion, any crack, or any severed lug; repetitive detailed and HFEC inspections of the left and right side-strut support fitting lugs with bushings removed for any corrosion or any crack; and applicable on-condition actions. \n\tWe are issuing this AD to address cracks caused by corrosion, which could result in sudden loss of the side-strut support fitting joint and main landing gear attachment to the airplane, resulting in the collapse of a main landing gear. \n\nComments \n\n\n\tWe gave the public the opportunity to participate in developing this final rule. The following presents the comments received on the NPRM and the FAA's response to each comment. \n\nEffect of Winglets on Accomplishment of the Proposed Actions \n\n\n\tAviation Partners Boeing stated that accomplishing Supplemental Type Certificate (STC) ST01219SE does not affect the actions specified in the proposed AD. \n\tWe concur with the commenter. We have 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 ST01219SE does not affect the ability to accomplish the actions required by this AD. Therefore, for airplanes on which STC ST01219SE 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. \n\nRequest To Change Format of Paragraphs (g) and (h) of the Proposed AD \n\n\n\tBoeing requested that we eliminate paragraph (h) of the proposed AD and incorporate the information as paragraph (g)(2) of this AD. Boeing pointed out that the title of paragraph (g) of the proposed AD would change to ''Required Actions,'' and that paragraphs (g)(1) and (g)(2) of this AD would apply to Group 7 and Groups 1 through 6, respectively. Boeing stated that this request is for consistency with previous ADs for Boeing airplanes. \n\tWe disagree that elimination of paragraph (h) of the proposed AD and incorporating the information as paragraph (g)(2) of this AD is necessary. Over time we have used both formats, but most recently we have been using the format that was utilized in the NPRM. We do not find that there is a difference in clarity of the required actions. We also find that the requested change does not affect the requirements \n\n((Page 26332)) \n\nof this finalrule in this case. We have not changed this AD in this regard. \n\nRequest To Clarify ACO Branch Authority \n\n\n\tBoeing requested that we clarify the ACO branch that has the authority to approve AMOCs for this group of airplanes. Boeing pointed out that previous final rules for The Boeing Company Model 737-100, - 200, -200C, -300, -400, and -500 series airplanes have identified The Manager, Los Angeles ACO Branch, FAA, had the authority to approve AMOCs, even when the service bulletin was submitted for approval through the Seattle ACO Branch. Additionally, Boeing pointed out that previous ADs for The Boeing Company Model 737-100, -200, -200C, -300, - 400, and -500 series airplanes identified a Los Angeles ACO Branch specialist in the ''Related Information'' paragraph of the proposed rule, even when the service bulletin was submitted for approval through the Seattle ACO Branch. \n\tWe agree that clarification is necessary. Normally, in NPRMs for The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 series airplanes, we include the Manager, Los Angeles ACO Branch, as the designated approval authority for AMOCs. We have updated paragraph (j) of this AD to specify The Manager, Los Angeles ACO Branch. The Seattle ACO Branch is responsible during drafting of the NPRM and final rule of an AD for The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. After publication of the final rule, responsibility for the product is transferred to the Los Angeles ACO Branch. Therefore, when we draft the final rule of an AD for The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 series airplanes, we also specify a specialist from the Los Angeles ACO Branch. We have updated paragraph (k) of this AD to include the responsible specialist from the Los Angeles ACO Branch. \n\nConclusion \n\n\n\tWe reviewed the relevant data, considered the comments received, and determined that air safety and the public interest require adopting thisfinal rule with the changes described previously and minor editorial changes. We have determined that these minor changes: \n\tAre consistent with the intent that was proposed in the NPRM for addressing the unsafe condition; and \n\tDo not add any additional burden upon the public than was already proposed in the NPRM. \n\tWe 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\tWe reviewed Boeing Service Bulletin 737-53-1246, Revision 1, dated May 30, 2018. This service information describes procedures for repetitive detailed inspections of the left and right side-strut support fitting lugs at body station (BS) 685 with bushings installed for any corrosion, any crack, or any severed lug; repetitive detailed and HFEC inspections of the left and right side-strut support fitting lugs at BS 685 with bushings removed for any corrosion or any crack; and applicable on-condition actions. On-condition actions include, among other things, inspections, corrosion removal, and a preventative modification. Doing the repetitive detailed and HFEC inspections of the side-strut support fitting lugs at BS 685 with bushings removed terminates the repetitive detailed inspections of the side-strut support fitting lugs at BS 685 with bushings installed. 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\tWe estimate that this AD affects 302 airplanes of U.S. registry. We estimate the following costs to comply with this AD: \n\n\n\tEstimated Costs for Required Actions ---------------------------------------------------------------------------------------------------------------- \n\tCost on U.S. \n\tAction Labor cost Parts cost Cost per product operators---------------------------------------------------------------------------------------------------------------- Repetitive detailed inspection 17 work-hours x $85 per $0 $1,445 per $436,390 per \n\tof left and right side lugs hour = $1,445 per inspection cycle. inspection cycle. \n\twith bushings installed. inspection cycle. Repetitive detailed and HFEC 29 work-hours x $85 per 0 $2,465 per $744,430 per \n\tinspections of left and right hour = $2,465 per inspection cycle. inspection cycle. \n\tside lugs with bushings inspection cycle. \n\tremoved. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tWe estimate the following costs to do any necessary on-condition actions that would be required. We have no way of determining the number of aircraft that might need these on-condition actions: \n\n\n\tEstimated Costs of On-Condition Actions ------------------------------------------------------------------------ \n\tLabor cost Parts cost Cost per product ------------------------------------------------------------------------ Up to 18 work-hour x $85 per Unknown........... Up to $1,530 per \n\thour = $1,530 per inspection inspection cycle. \n\tcycle. ------------------------------------------------------------------------ \n\n\n\tWe have received no definitive data that would enable us to provide parts cost estimates for the on-condition inspections and repairs 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\tWe are 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 \n\n((Page 26333)) \n\nis 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\tThis AD is issued in accordance with authority delegated by the Executive Director, Aircraft Certification Service, as authorized by FAA Order 8000.51C. In accordance with that order, issuance of ADs is normally a function of the Compliance and Airworthiness Division, but during this transition period, the Executive Director has delegated the authority to issue ADs applicable to transport category airplanes and associated appliances to the Director of the System Oversight Division. \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) Is not a ''significant rule'' under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979), \n\t(3) Will not affect intrastate aviation in Alaska, and \n\t(4) 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.