Airworthiness Directives; Air Tractor, Inc. AT-400, AT-500, AT-600, and AT-800 Series Airplanes

We are adopting a new airworthiness directive (AD) to supersede AD 2007-13-17, which applies to certain Air Tractor, Inc. (Air Tractor) Models AT-602, AT-802, and AT-802A airplanes. AD 2007-13- 17 currently requires you to repetitively inspect the engine mount for any cracks, repair or replace any cracked engine mount, and report any cracks found to the FAA. Since we issued AD 2007-13-17, Air Tractor has learned of a Model AT-502B with a crack located where the lower engine mount tube is welded to the engine mount ring. In addition, Air Tractor has developed gussets that, when installed according to their service letter, terminate the repetitive inspection requirement. Consequently, this AD would retain the inspection actions of AD 2007-13-17 for Model AT-602, AT-802, and AT-802A airplanes, including the compliance times and effective dates; establish new inspection actions for the AT-400 and AT-500 series airplanes; incorporate a mandatory terminating action for all airplanes; and terminate the reporting requirement of AD 2007- 13-17. We are issuing this AD to detect and correct cracks in the engine mount, which could result in failure of the engine mount. Such failure could lead to separation of the engine from the airplane.