Airworthiness Directives; Air Tractor, Inc. Models AT-400, AT-400A, AT-402, AT-402A, AT-402B, AT-502, AT-502A, AT-502B, AT-503A, AT-602, AT-802, and AT-802A Airplanes

We are adopting a new airworthiness directive (AD) to supersede AD 2008-10-12, which applies to certain Air Tractor, Inc. AT- 400, AT-500, AT-600, and AT-800 series airplanes. AD 2008-10-12 currently requires repetitively inspecting the engine mounts for cracks, repairing any crack damage found, and installing gussets as a terminating action for the repetitive inspections. This AD results from a report of a Model AT-602 airplane with a crack completely through the gusset that was installed as required in AD 2008-10-12. Consequently, this AD would require you to continue repetitively inspecting the engine mounts for cracks for all previously affected Air Tractor, Inc. AT-400, AT-500, AT-600, and AT-800 series airplanes with or without gussets installed, and repairing any crack damage found. We are issuing this AD to detect and correct cracks in the engine mount, which could result in failure of the engine mount. This failure could lead to separation of the engine from the airplane.