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

This document publishes in the Federal Register an amendment adopting superseding Airworthiness Directive (AD) 2000-23-52, which was sent previously to all known U.S. owners and operators of Sikorsky Aircraft Corporation (Sikorsky) Model S-76A, S-76B, and S-76C helicopters by individual letters. This AD requires, before further flight, performing a fluorescent penetrant inspection of the main rotor shaft assembly (shaft). Also required are recurring fluorescent penetrant inspections and visual inspections for any crack. If any crack is found, the shaft must be replaced with an airworthy shaft before further flight. This amendment is prompted by the discovery of two in-service cracked shafts, one with 477 hours time-in-service (TIS) and one with 313 hours TIS. A third shaft, that had been rejected from the manufacturing process for other reasons, was also discovered to have a crack. The actions specified by this AD are intended to prevent failure of the shaft and subsequent loss of control of the helicopter.