Airworthiness Directives; Sikorsky Aircraft-Manufactured Model CH-54B Helicopters

This amendment adopts a new airworthiness directive (AD), applicable to Sikorsky Aircraft-manufactured Model CH-54B helicopters, that requires initial and recurring inspections and rework or replacement, if necessary, of the second stage lower planetary plate (plate). This amendment is prompted by two reports of cracked plates that have been found during overhaul and inspections. The actions specified by this 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.