AD FAA-2011-0548

We are adopting a new airworthiness directive (AD) for the Sikorsky Model S-92A helicopters. This AD requires a nondestructive inspection (NDI), eddy current or fluorescent penetrant inspection (FPI), of each main gearbox (MGB) upper housing assembly rib on the left, right, and forward MGB mounting foot at specified intervals based on the MGB upper housing assembly hours time-in-service (TIS). If there is a crack, this AD requires replacing the MGB upper housing assembly with an airworthy MGB upper housing assembly. This AD is prompted by a report of a crack found on the MGB upper housing assembly left mounting foot forward rib that cannot be detected visually. We are issuing this AD to prevent loss of the MGB and subsequent loss of control of the helicopter.