Summary
We propose to supersede an existing airworthiness directive (AD) for Sikorsky Aircraft Corporation-manufactured Model S-64E helicopters (type certificate currently held by Erickson Air-Crane Incorporated (Erickson)). That AD currently requires inspecting and reworking the main gearbox (MGB) assembly second stage lower planetary plate (plate). This action would establish or reduce the life limits for certain flight-critical components, remove from service various parts, require repetitive inspections and other corrective actions, and require replacing any cracked part discovered during an inspection. This proposal is prompted by further analysis performed by the current type certificate holder and the service history of certain parts. The actions specified in the proposed AD are intended to prevent a crack in a flight critical component, failure of a critical part, and subsequent loss of control of the helicopter.