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 \n\n((Page 46381)) \n\n737-100, -200, -200C, -300, -400, and -500 series airplanes. The NPRM published in the Federal Register on February 21, 2018 (83 FR 7425). The NPRM was prompted by reports of cracking in certain flanges, and the adjacent web, of the wing outboard flap track at certain positions, and a determination that new inspections of certain flap track flanges and webs forward of the rear spar attachment are necessary. The NPRM proposed to require an inspection to determine the part number of the wing outboard flap track assembly; repetitive inspections of each affected wing outboard flap track for discrepancies, and applicable on- condition actions; and repetitive overhaul of each wing outboard flap track. \n\tWe are issuing this AD to detect and correct cracking of the wing outboard flap tracks. Cracking in the area between the forward and rear spar attachments of the wing outboard flap tracks could lead to the inability of a principal structural element to sustain required flight loads, and result in loss of the outboard trailing edge flap and consequent reduced controllability of the airplane. \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\nRequest To Extend the Compliance Time \n\n\n\tAll Nippon Airways (ANA) and Utair Aviation requested that paragraph (h) of the proposed AD be revised to extend the compliance time from 6 months to 18 months after the effective date of the final rule. The commenters are concerned that there are not enough spare flap track parts available. The commenters indicated that overhaul of the removed flap tracks takes significant time, and if the final rule is released without a sufficient number of spare flap tracks available, there could be a long-term aircraft on ground (AOG) situation if the proposed compliance times are used. \n\tFurthermore, Utair Aviation stated that a review of maintenance records on 38 airplanes for flap tracks at positions 1 and 8 did not find any records of inspections or overhaul, and it would not be able to replace the subject flap tracks within the compliance time specified in the proposed AD. Utair Aviation also noted that it took 60 days, including shipping, to replace the outboard flap tracks for similar requirements specified in AD 2013-09-02, Amendment 39-17443 (78 FR 27010, May 9, 2013). \n\tWe do not agree with the commenters' requests. The 6-month compliance time for inspection and overhaul is applicable only to flap tracks that have unknown maintenance records and flap tracks that were last overhauled several years ago. Airplanes with flap tracks that have known maintenance records generally have later compliance times, depending on howlong it has been since the flap tracks were overhauled. The NPRM was issued to address findings of stress corrosion cracking in the flap tracks. Stress corrosion cracking is more likely to occur in flap tracks that have been in operation for a longer time. Flap tracks with unknown maintenance records and flap tracks that were last overhauled several years ago are more susceptible to the unsafe condition. The probability of the existence of stress corrosion cracking on flap tracks with unknown maintenance history is higher and warrants the shorter compliance time. We have verified that spare flap tracks are available on the parts surplus market; however, since we do not know how many flap tracks have unknown maintenance records, it is difficult to estimate how many spare flap tracks will be necessary to meet the demand. If there is a critical shortage of parts, operators may contact the FAA and request an adjustment to the compliance time using the procedures specified in paragraph (l)of this AD. We might approve a longer compliance time if additional data are presented that would justify an extension to the compliance time while still maintaining an adequate level of safety. \n\tWe urge operators to seek out maintenance records for their flap tracks in order to justify use of the extended compliance times specified in Boeing Alert Requirements Bulletin 737-57A1338 RB, dated September 25, 2017. We cannot justify extending the compliance times for flap tracks without maintenance records to 18 months. We have not changed this AD in regard to this issue. \n\nRequest To Omit Inspection 1 in the Service Information \n\n\n\tUtair Aviation stated that it is inadvisable to require operators to do the inspections included in ''INSPECTION 1,'' as defined in Boeing Alert Requirements Bulletin 737-57A1338 RB, dated September 25, 2017. The commenter noted that ''ACTION 1'' in Table 1 and Table 2 of paragraph 3, ''Compliance,'' of Boeing Alert Requirements Bulletin 737- 57A1338 RB, dated September 25, 2017, states that operators need to do INSPECTION 1. The commenter suggested that ''ACTION 2,'' overhaul of each affected flap track, would already include all of the inspections included in INSPECTION 1. \n\tWe infer that the commenter is requesting that the proposed requirement to do the inspections included in INSPECTION 1 of the specified service bulletin be removed from the proposed AD. We do not agree with the commenter's request. ACTION 1 and ACTION 2 have different purposes. The inspections included in ACTION 1 are intended to detect specific existing damage on the flap track, including cracks, nicks, corrosion, galling, broken pieces, and stop drills. The intention of ACTION 2, overhaul of each affected flap track, is a visual examination for defects. The intent of this visual examination during overhaul is to identify additional discrepancies, such as excessive wear or degraded surface finish, that might not be noted during INSPECTION 1. It is important to detect these additional discrepancies since they can be early indicators of stress corrosion cracking. Since the inspections to detect specific existing damage on the flap track are not included in the overhaul instructions, it is necessary to require both ACTION 1 and ACTION 2 in this AD. We have not changed this AD in regard to this issue. \n\nRequest for Alternative To Overhaul \n\n\n\tANA requested that an alternative to overhaul of the flap tracks be provided that does not involve removing the flap tracks from the wing. The commenter suggested that an on-wing inspection could be used instead of the overhaul. The commenter is concerned that there is not a sufficient supply of spare flap track parts. \n\tWe do not agree with the commenter's request. There is no on-wing inspection method available that can detect the additional discrepancies that overhaul of the flap tracks is designed to address. The concern regarding availability of spare flap track parts was addressed in the response to an earlier comment. We have not changed this AD in regard to this issue. \n\nRequest To Revise Parts Installation Limitation Paragraph \n\n\n\tBoeing requested that the Parts Installation Limitation Paragraph, paragraph (k) in the proposed AD, be revised to allow flap tracks to be installed and inspected at the time of installation. Boeing noted that paragraph (k) states ''. . . no person may install a flap track unless the flap track is inspected prior to installation.'' Boeing pointed out that there are several \n\n((Page 46382)) \n\ninspections that pertain to the track-to-wing joint, which cannot be accomplished until after the flap track is installed. \n\tWe agree with the commenter's request for the reasons provided by the commenter. We have revised paragraph (k) of this AD to state ''As of the effective date of this AD, no person may install, on any airplane, a wing outboard flap track having a part number listed in paragraph 1.B. of Boeing Alert Requirements Bulletin 737-57A1338 RB, dated September 25, 2017, unless the inspections . . . are accomplished prior to or concurrently with the part's installation on the airplane.'' \n\nEffect of Winglets on Accomplishment of the Proposed Actions \n\n\n\tAviation Partners Boeing stated that accomplishing the installation of winglets using Supplemental Type Certificate (STC) ST01219SE does not affect compliance with the actions proposed in the NPRM. \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\nAdditional Change to This AD \n\n\n\tThe proposed AD included Note 1 to paragraph (h),which stated that guidance for accomplishing the proposed actions could be found in Boeing Alert Service Bulletin 737-57A1338, dated September 25, 2017, which is referred to in Boeing Alert Requirements Bulletin 737-57A1338 RB, dated September 25, 2017. Since the proposed AD was published, Boeing has issued Boeing Information Notice 737-57A1338 IN 01, dated October 16, 2017; Boeing Information Notice 737-57A1338 IN 02, dated March 16, 2018; and Boeing Information Notice 737-57A1338 IN 03, dated March 20, 2018. These information notices provide additional guidance material related to Boeing Alert Service Bulletin 737-57A1338, dated September 25, 2017, including clarification of compliance times for spares (not AD compliance times), inspection figures, and the relationship between flap track part numbers and airplanes groups. We have revised Note 1 to paragraph (h) in this AD to include these information notices. \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 this final 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 Alert Requirements Bulletin 737-57A1338 RB, dated September 25, 2017. This service information describes procedures for repetitive inspections and repetitive overhaul of the wing outboard flap tracks, and applicable on-condition actions including repair and replacement of the wing outboard flap tracks. 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 160 airplanes of U.S. registry. We estimate the following costs to comply with this AD: \n\n\n\tEstimated Costs for Required Actions -------------------------------------------------------------------------------------------------------------------------------------------------------- \n\tAction Labor cost Parts cost Cost per product Cost on U.S. operators -------------------------------------------------------------------------------------------------------------------------------------------------------- Inspection (positions 1 and 8; 78 work-hours x $85 $0 $6,630 per cycle................. $1,060,800 per cycle. \n\tGroup 2 and Group 3, configuration per hour = $6,630 per \n\t1). cycle. Inspection (positions 1 and 8; 89 work-hours x $85 0 7,565 per cycle.................. 1,210,400 per cycle. \n\tGroup 3, configuration 2). per hour = $7,565 per \n\tcycle. Inspection (positions 2 and 7; 83 work-hours x $85 0 7,055 per cycle.................. 1,128,800 per cycle. \n\tGroup 2 and Group 3, configuration per hour = $7,055 per \n\t1). cycle. Inspection (positions 2 and 7; 86 work-hours x $85 0 7,310 per cycle.................. 1,169,600 per cycle. \n\tGroup 3, configuration 2). per hour = $7,310 per \n\tcycle. -------------------------------------------------------------------------------------------------------------------------------------------------------- \n\n\n\tWe have received no definitive data that will enable us to provide cost estimates for the actions for Group 1 airplanes, the repetitive overhaul, or 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\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 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\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 \n\n((Page 46383)) \n\nthe 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.