Summary
This document proposes to adopt a new airworthiness directive (AD) that would apply to certain Air Tractor, Inc. (Air Tractor) Models AT-300, AT-400, AT-400A, AT-401, AT-401B, AT-402, AT-402A, AT-402B, AT-501, AT-502, and AT-502B airplanes. This proposed AD would require you to repetitively inspect the vertical fin front spar fitting for cracks and replace any cracked fitting found. This proposed AD would also require you to install a steel doubler as a terminating action for the repetitive inspections. This proposed AD is the result of a report of failure of a 1/4-inch thick vertical fin front spar fitting. The actions specified by this proposed AD are intended to prevent failure of the vertical fin front spar fitting, which could result in failure of the rear spar fitting. Such failures could lead to loss of directional control of the airplane.