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

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We propose to supersede an existing airworthiness directive (AD) for the Sikorsky Aircraft Corporation-manufactured Model S-64F helicopters, now under the Erickson Air-Crane Incorporated (Erickson) Model S-64F type certificate. That AD currently requires inspections, rework, and replacement, if necessary, of the main gearbox (MGB) second stage lower planetary plate (plate). Since we issued that AD, the manufacturer has conducted a configuration review and analysis, and a review of the service history of certain components. The proposed actions are intended to establish life limits for certain components, remove various parts from service, and require consistency in the part numbers of certain four bladed tail rotor (T/R) assemblies to prevent fatigue cracking, failure from static overload, and subsequent loss of control of the helicopter.