Airworthiness Directives; Sikorsky Aircraft-Manufactured Model S- 64F Helicopters

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This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Sikorsky Aircraft-manufactured S- 64F helicopters. This proposal would require inspections, and replacement, if necessary, of the main gearbox second stage lower planetary plate (plate). This proposal is prompted by two incidents in which the second stage planetary plate was found cracked. The actions specified by the proposed AD are intended to prevent failure of the plate due to fatigue cracking, which could lead to failure of the main gearbox and subsequent loss of control of the helicopter.