Airworthiness Directives; Air Tractor, Inc. Models AT-300, AT-301, AT-302, AT-400, and AT-400A Airplanes

This amendment adopts a new airworthiness directive (AD) that applies to all Air Tractor, Inc. (Air Tractor) Models AT-300, AT-301, AT-302, and AT-400A airplanes that have aluminum spar caps; certain Air Tractor Models AT-400 airplanes that have aluminum spar caps; and all Models AT-300 and AT-301 airplanes that have aluminum spar caps and are or have been converted to turbine power. This AD requires you to inspect (one-time) the wing centerline splice joint for cracks and, if any crack is found, replace the affected wing spar lower cap. This AD also requires you to report the results of the inspection to the Federal Aviation Administration (FAA) and replace the wing spar lower caps after a certain amount of usage. This AD is the result of an incident on one of the affected airplanes where the wing separated from the airplane. Preliminary reports indicate that fatigue caused the lower aluminum spar cap to fail across the \3/8\-inch bolt hole (6.5 inches outboard of the fuselage centerline in the centersplice connection). The actions specified by this AD are intended to detect and correct cracks in the wing centerline splice joint. If not detected and corrected, these cracks could eventually result in the wing separating from the airplane during flight.