Summary
We propose to adopt a new airworthiness directive (AD) for certain Air Tractor, Inc., (Air Tractor) Models AT-402, AT-402A, and AT-402B airplanes. This proposed AD would require you to repetitively visually inspect the rudder and vertical fin hinge attaching structure for loose fasteners and inspect the rudder or vertical fin skins, spars, hinges or brackets for cracks and/or corrosion. The AD would also require you to replace any damaged parts found as a result of the inspections and install an external doubler at the upper rudder hinge. Installation of the external doubler at the upper rudder hinge is terminating action for the repetitive inspection requirements. This proposed AD results from a report of a Model AT-402 airplane with a loose upper rudder hinge caused by fatigue. We are proposing this AD to detect and correct loose fasteners; any cracks in the rudder or vertical fin skins, spars, hinges or brackets; or corrosion of the rudder and vertical fin hinge attaching structure. Hinge failure adversely affects ability to control yaw and has led to the rudder folding over in flight. This condition could allow the rudder to contact the elevator and affect ability to control pitch with consequent loss of control.