Airworthiness Directives; Sikorsky Aircraft Corporation Model S-92A Helicopters

This amendment adopts a new airworthiness directive (AD) for the Sikorsky Aircraft Corporation (Sikorsky) Model S-92A helicopters. This action requires, before further flight, replacing a certain main gearbox (MGB) upper main housing assembly (housing assembly) that has 2700 or more hours time-in-service (TIS) with an airworthy part. This action also requires, before further flight, revising the Airworthiness Limitations section (ALS) of the maintenance manual by establishing a new retirement life for the MGB housing assembly of 2700 hours TIS. This amendment is prompted by testing of the MGB housing assembly that resulted in premature fatigue failure due to a manufacturing process creating an oxide skin defect in the housing. The actions specified in this AD are intended to prevent fatigue failure of the MGB housing, loss of MGB lube oil, loss of main and tail rotor drive, and subsequent loss of control of the helicopter.