Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Sikorsky Aircraft-manufactured Model CH-54B helicopters. This proposal would require initial and recurring inspections and rework or replacement, if necessary, of the second stage lower planetary plate (plate). This proposal is prompted by two reports of cracked plates that have been found during overhaul and inspections. The actions specified by the proposed AD are intended to prevent failure of the main gearbox plate due to fatigue cracking, which could lead to failure of the main gearbox and subsequent loss of control of the helicopter.