Airworthiness Directives; Enstrom Helicopter Corporation Model F-28, F-28A, F-28C, F-28F, 280, 280C, 280F, and 280FX Helicopters

This amendment supersedes an existing airworthiness directive (AD) for Enstrom Helicopter Corporation (EHC) Model F-28, F-28A, F-28C, F-28F, 280, 280C, 280F, and 280FX helicopters. That AD currently requires determining the radius of the shaft fillet, performing certain visual and dye-penetrant inspections before further flight, and replacing certain main rotor transmissions. This amendment requires the same actions as the previous AD, adds additional main rotor gear box part numbers, and corrects various errors contained in the current AD. This amendment is prompted by a commenter who noted that two additional main rotor gear box part numbers should have been included in the AD. The actions specified by this AD are intended to prevent shaft failure and subsequent loss of control of the helicopter.