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

This amendment revises AD 2001-10-04, which concerns certain Air Tractor, Inc. (Air Tractor) AT-400, AT-500, and AT-800 series airplanes. AD 2001-10-04 superseded AD 2000-14-51 and lowers the safe life for the wing lower spar cap on these airplanes. The AD was the result of numerous reports of cracks in the 3/8-inch bolthole of the wing lower spar cap on the affected airplanes. We inadvertently included certain AT-800 series airplanes in the Applicability of this AD. Those AT-800 series airplanes that are equipped with the factory- supplied part number 80540 computerized fire gate should not be affected by AD 2001-10-04. This action revises the AD to reflect this change and to provide information for applying for an alternative method of compliance with this AD. The actions specified by this AD are intended to prevent fatigue cracks from occurring in the wing lower spar cap before the originally established safe life is reached. Fatigue cracks in the wing lower spar cap, if not detected and corrected, could result in the wing separating from the airplane during flight.