Airworthiness Directives; Air Tractor, Inc. Models AT-400, AT-401, AT-401B, AT-402, AT-402A, AT-402B, AT-501, AT-802, and AT-802A Airplanes

This amendment supersedes Airworthiness Directive (AD) 2001- 10-04 R1, which lowered the safe life for the wing lower spar cap on certain Air Tractor, Inc. (Air Tractor) AT-400, AT-500, and AT-800 series airplanes. AD 2001-10-04 R1 resulted from numerous reports of cracks in the \3/8\-inch bolthole of the wing lower spar cap on the affected airplanes. This AD retains the safe life for the wing lower spar cap and requires you to eddy-current inspect the wing lower spar cap immediately prior to the replacement/modification in order to detect and correct any crack in a bolthole before it extends to the modified center section of the wing. This AD further reduces the safe life for certain Models AT-401, AT-401B, AT-402, AT-402A, AT-402B, and AT-501 airplanes that incorporate or have incorporated Marburger Enterprises, Inc. winglets and removes the Models AT-502, AT-502A, AT- 502B, and AT-503A airplanes from the applicability. We are issuing another AD action to cover these airplanes. The actions specified by this AD are intended to prevent fatigue cracks from occurring in the wing lower spar cap before the 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.