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Federal Register / Vol. 86, No. 56 / Thursday, March 25, 2021 / Rules and Regulations other information. The address for Docket Operations is U.S. Department of Transportation, Docket Operations, M
30, West Building Ground Floor, Room W12140, 1200 New Jersey Avenue SE, Washington, DC 20590.
FOR FURTHER INFORMATION CONTACT:
Kenneth A. Cook, Aviation Safety Engineer, Fort Worth ACO Branch, AIR
7F0, FAA, 10101 Hillwood Pkwy., Fort Worth, TX 76177; phone: 817 222
5475; email: kenneth.a.cook@faa.gov.
SUPPLEMENTARY INFORMATION:

Requests Regarding the Compliance Times
The 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 AT250, AT300, AT301, AT302, AT400, AT400A, AT401, AT401A, AT
401B, AT402, AT402A, AT402B, AT501, AT502, AT502A, AT502B, AT503, AT503A, AT504, AT602, AT802, and AT802A 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.
One of the reports was on a Model AT802A 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 cracks in the flap torque tube attachment brackets.
The design of the flap actuator motor brackets on the Model AT802A
airplane is the same as on Models AT
250, AT300, AT301, AT302, AT
400, AT400A, AT401, AT401A, AT
401B, AT402, AT402A, AT402B, AT501, AT502, AT502A, AT503, AT503A, AT504, AT602, and AT
802 airplanes.
In 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.

Air 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.
The 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.
Air 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.
The 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.
Field 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.
The FAA acknowledges this comment and has changed the compliance time for the visual inspections from 300
hours TIS to 345 hours TIS.

Discussion of Final Airworthiness Directive Comments
Request To Allow Replacement Parts With More Than Zero Hours TIS

The 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 FAAs response to each comment.

Air 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
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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.
The 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.
Request Regarding Reporting Requirement Air 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 reporting is 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.
The 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.
Request To Expand Service Letter References Air Tractor requested that the requirement in the AD to perform a dye penetrant inspection include step 4B1
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.
The FAA disagrees with adding step 4B1 since this step is not required to address the unsafe condition.
Air Tractor also requested the AD
require step 4B11 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 CE1826, 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.
The 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
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