Background \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 all Air Tractor Models AT-250, AT-300, AT-301, AT-302, AT-400, AT-400A, AT-401, AT-401A, AT- 401B, AT-402, AT-402A, AT-402B, AT-501, AT-502, AT-502A, AT-502B, AT- 503, AT-503A, AT-504, AT-602, AT-802, and AT-802A airplanes. The NPRM published in the Federal Register on July 28, 2020 (85 FR 45347). The NPRM was prompted by multiple reports of cracks in the brackets attaching the flap actuator motor to the flap torque tube on several models of Air Tractor airplanes. \n\tOne of the reports was on a Model AT-802A airplane where the brackets separated from the torque tube at the welds. The flaps suddenly retracted while maneuvering, and the pilot temporarily lost control of the airplane. The pilot was able to regain control of the airplane before it impacted the ground. Since then, there have been 13 reported airplanes with cracksin the flap torque tube attachment brackets. \n\tThe design of the flap actuator motor brackets on the Model AT-802A airplane is the same as on Models AT-250, AT-300, AT-301, AT-302, AT- 400, AT-400A, AT-401, AT-401A, AT-401B, AT-402, AT-402A, AT-402B, AT- 501, AT-502, AT-502A, AT-503, AT-503A, AT-504, AT-602, and AT-802 airplanes. \n\tIn the NPRM, the FAA proposed to require repetitive dye penetrant and visual inspections with replacement of the flap torque tube if cracks are found. The FAA is issuing this AD to address the unsafe condition on these products. \n\nDiscussion of Final Airworthiness Directive Comments \n\n\n\tThe FAA received comments from two commenters. The commenters were Air Tractor and Field Air Sales and Maintenance Pty Ltd (Field Air). The following presents the comments received on the NPRM and the FAA's response to each comment. \n\nRequests Regarding the Compliance Times \n\n\n\tAir Tractor requested the FAA clarify whether the hours time-in- service (TIS) compliance times are based on aircraft time or flap torque tube component time. The commenter requested that the AD require compliance based on the hours TIS of the flap torque tube component to account for new torque tubes installed on an existing aircraft. \n\tThe FAA disagrees with this comment. The hours TIS compliance required by this AD refers to the hours TIS the airplane operates after the effective date of the AD and after each inspection. Air Tractor has not provided data analysis to identify the root cause of the failures of the torque tubes or to indicate whether the failures are related to the hours TIS of the torque tubes. \n\tAir Tractor and Field Air requested the FAA remove the proposed requirement to perform a dye penetrant inspection within 300 hours TIS after the effective date of the AD. Air Tractor said the proposed requirement does not provide consideration for flap torque tubes that have accumulated less than 900 hours and requested the FAA instead require visual inspections every 300 hours until the flap torque tube accumulates 900 hours TIS. Field Air requested the FAA provide its justification for requiring a dye penetrant inspection within 300 hours TIS. \n\tThe FAA disagrees with this comment. The FAA has received no data to indicate that torque tubes with less than 900 hours TIS are unaffected by the unsafe condition. The initial dye penetrant inspection should reveal cracking that might be present on affected airplanes and ensure those cracks are addressed before the repetitive visual and dye penetrant inspections start. \n\tField Air requested the FAA explain why the proposed AD does not allow the +/- 15 percent tolerance for the visual inspections as specified in Air Tractor Service Letter #347, Revision A, dated December 9, 2019 (SL #347A). \n\tThe FAA acknowledges this comment and has changed the compliance time for the visual inspections from 300 hours TIS to 345 hours TIS. \n\nRequest To Allow Replacement Parts With More Than Zero Hours TISAir Tractor and Field Air disagreed with the proposal to replace a cracked torque tube with a new (zero hours time-in-service) torque tube. Field Air requested the FAA explain its justification for this proposal. Air Tractor stated there is no safety reason to require replacement with a zero-time flap torque tube instead of a flap torque tube that has passed the inspection. Air Tractor noted that allowing replacement with an airworthy flap torque tube would minimize aircraft down time. \n\tThe FAA agrees with this comment and has changed the AD to allow the replacement with a used (more than zero hours TIS) torque tube provided the dye penetrant inspection was completed and the part passed the inspection. \n\nRequest Regarding Reporting Requirement \n\n\n\tAir Tractor requested the FAA add a statement to the AD that the agency recommends that cracks be reported to the FAA or to Air Tractor for tracking. Air Tractor stated the language used in the proposed AD suggests that reportingis no longer recommended. Field Air requested the FAA explain its justification for not having a requirement in the AD to report to Air Tractor any cracked welds identified during the inspections. \n\tThe FAA acknowledges this comment. This AD is not an interim action. Mandating a report of the results of the inspection is not necessary to correct the unsafe condition. However, the FAA agrees that voluntarily reporting to Air Tractor when cracks are found could aid safety analysis of the fleet. \n\nRequest To Expand Service Letter References \n\n\n\tAir Tractor requested that the requirement in the AD to perform a dye penetrant inspection include step 4B(1) from SL #347A, which specifies gaining access to the flap actuator area by removing skin panels and conducting a visual inspection of the flap control system. \n\tThe FAA disagrees with adding step 4B(1) since this step is not required to address the unsafe condition. \n\tAir Tractor also requested the AD require step 4B(11) from SL #347A, which specifies recording in the aircraft records the results of the dye penetrant inspection and what type of dye penetrant was used. Air Tractor referenced the recommendations in FAA Special Airworthiness Bulletin CE-18-26, Liquid Penetrant Inspection: Using Visible Dye Penetrant, dated September 4, 2018, and noted that the type of dye penetrant is important information for future inspections. \n\tThe FAA disagrees that a change to the AD is necessary. Persons performing maintenance are required by 14 CFR part 43 to make an entry in the airplane maintenance records describing the \n\n((Page 15786)) \n\nwork performed. That description should identify the same information specified in step 4B(11). \n\tThe FAA did not change this AD based on this comment. \n\nConclusion \n\n\n\tThe FAA reviewed the relevant data, considered any comments received, and determined that air safety requires adopting this AD as proposed. Accordingly, the FAA is issuing this AD to address the unsafe condition on these products. 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. \n\nRelated Service Information Under 1 CFR Part 51 \n\n\n\tThe FAA reviewed Air Tractor, Inc. Service Letter #347, Revision A, dated December 9, 2019. The service letter specifies procedures for repetitive visual inspections and dye penetrant inspections of the flap torque tube brackets for cracks and instructs operators to replace the torque tube as 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. \n\nDifferences Between the AD and the Service Information \n\n\n\tAir Tractor SL #347, Rev A specifies performing the dye penetrant inspection within 900 hours TIS, and this AD requires the initial dye penetrant inspection within 300 hoursTIS. Air Tractor SL #347, Rev A specifies replacing a cracked torque tube, while this AD requires replacing a cracked torque tube with a torque tube that has zero hours TIS. Air Tractor SL #347, Rev A specifies reporting any cracked welds identified during the inspections. \n\nCosts of Compliance \n\n\n\tThe FAA estimates that this AD affects 1,662 airplanes of U.S. registry. \n\tThe FAA estimates the following costs to comply with this AD: \n\n\n\tEstimated Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost on U.S. \n\tAction Labor cost Parts cost Cost per product operators ---------------------------------------------------------------------------------------------------------------- Dye penetrant inspection........ 4 work-hours x $85 Not applicable.... $340 per $565,080 per \n\tper hour = $340 inspection cycle. inspection cycle \n\tperinspection \n\tcycle. Visual inspection............... .5 work-hour x $85 Not applicable.... $42.50............ $70,635 per \n\tper hour = $42.50 inspection cycle \n\tper inspection \n\tcycle. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tThe FAA estimates the following costs to do any necessary replacements that will be required based on the results of the inspection. The FAA has no way of determining the number of airplanes that might need this replacement. \n\n\n\tOn-Condition Costs for Model AT-802 and AT-802A \n\t(Potential 485 Airplanes) ---------------------------------------------------------------------------------------------------------------- \n\tCost per \n\tAction Labor cost Parts cost product ---------------------------------------------------------------------------------------------------------------- Replacement of torque tube................... 3 work-hours x $85 per hour = $1,292 $1,547 \n\t$255. ---------------------------------------------------------------------------------------------------------------- \n\n\n\n\n\tOn-Condition Costs for Model AT-602 \n\t(Potential 236 Airplanes) ---------------------------------------------------------------------------------------------------------------- \n\tCost per \n\tAction Labor cost Parts cost product ---------------------------------------------------------------------------------------------------------------- Replacement of torque tube................... 3 work-hours x $85 per hour = $1,140 $1,395 \n\t$255. ---------------------------------------------------------------------------------------------------------------- \n\n\n\n\n\tOn-Condition Costs for Models AT-501, AT-502, AT-502A, AT-502B, AT-503, AT-503A, and AT-504 \n\t(Potential 512 Airplanes)---------------------------------------------------------------------------------------------------------------- \n\tCost per \n\tAction Labor cost Parts cost product ---------------------------------------------------------------------------------------------------------------- Replacement of torque tube................... 3 work-hours x $85 per hour = $955 $1,210 \n\t$255. ---------------------------------------------------------------------------------------------------------------- \n\n\n\nOn-Condition Costs for Models AT-250, AT-300, AT-301, AT-302, AT-400, AT-400A, AT-401, AT-401A, AT-401B, AT-402, \n\tAT-402A, and AT-402B \n\t(Potential 429 Airplanes) ---------------------------------------------------------------------------------------------------------------- \n\tCost per \n\tAction Labor cost Parts cost product ---------------------------------------------------------------------------------------------------------------- Replacement of torque tube................... 3 work-hours x $85 per hour = $927 $1,182 \n\t$255. ---------------------------------------------------------------------------------------------------------------- \n\n\n\n((Page 15787)) \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 inair 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, Incorporationby reference, Safety.