Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to McDonnell Douglas Helicopter Systems (MDHS) Model 369D, 369E, 369FF, 369H, MD500N, and MD600N helicopters. This proposal would require a one-time visual inspection of certain input shaft coupling assemblies for pitting. This proposal is prompted by three operators' reports of discovering pitting on the internal spline teeth. The actions specified by the proposed 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.