Airworthiness Directives; Sikorsky Aircraft Corporation Model S-76 A, B, and C Helicopters

This amendment adopts a new airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S-76 A, B, and C helicopters with dual channel autopilot and dual inverters installed. This action requires a test to determine if the No. 1 inverter is wired to the DC essential bus, and if so, it requires modifying the wiring so that the No. 1 inverter is wired to the No. 2 DC primary bus and the No. 2 inverter is wired to the DC essential bus. If the wiring modification is required and is not performed before further flight, then revising the Rotorcraft Flight Manual (RFM) before further flight to limit the maximum instrument meteorological conditions (IMC) airspeed and installing a placard near the airspeed indicator is also required. The wiring modification is required within 30 days. This amendment is prompted by three incidents in which a No. 2 generator intermittent malfunction occurred and both autopilots disengaged. The actions specified in this AD are intended to prevent both autopilots from disengaging following a No. 2 DC generator failure, and subsequent loss of control of the helicopter during IMC operations.