Airworthiness Directives; Sikorsky Aircraft Corporation Model S-76A, S-76B, and S-76C Helicopters

This amendment supersedes an existing airworthiness directive (AD) that applies to Sikorsky Aircraft Corporation (Sikorsky) Model S- 76A, S-76B, and S-76C helicopters and currently requires, before further flight, performing a fluorescent penetrant inspection (FPI) of the main rotor shaft assembly (shaft). Also, a recurring FPI and visual inspection for a cracked shaft are required by that AD. That AD also requires replacing the shaft with an airworthy shaft before further flight if a crack is found. This amendment requires replacing certain serial numbered shafts with an airworthy shaft before further flight. This amendment is prompted by further investigation and a determination that the inspections can be safely eliminated if certain serial- numbered shafts are removed from service before further flight. The actions specified by this AD are intended to prevent failure of the shaft and subsequent loss of control of the helicopter.