Summary
This document proposes superseding an existing airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S- 61A, D, E, L, N, NM, R, and V helicopters. That AD currently requires a nondestructive inspection (NDI) for a crack in the main rotor shaft (shaft) and replacing any cracked shaft. This action would require establishing and defining new life limits and removing certain shafts from service. This proposal is prompted by the final results of fatigue tests indicating the need to establish life limits for certain shafts. The actions specified by the proposed AD are intended to prevent structural failure of the shaft, loss of power to the main rotor, and subsequent loss of control of the helicopter.