Airworthiness Directives; McDonnell Douglas Helicopter Systems Model 369D, 369E, 369FF, 369H, MD500N, and MD600N Helicopters

This amendment adopts a new airworthiness directive (AD), applicable to McDonnell Douglas Helicopter Systems (MDHS) Model 369D, 369E, 369FF, 369H, MD500N, and MD600N helicopters, that requires a one- time visual inspection of certain input shaft coupling assemblies for pitting. This amendment is prompted by three operators' reports of discovering pitting on the internal spline teeth. The actions specified by this AD are intended to prevent failure of the spline teeth in the input shaft coupling assembly, loss of drive to the main rotor system, and subsequent loss of control of the helicopter.