Airworthiness Directive · Amendment 39-13530 · Sikorsky Aircraft Corporation Model S-76 A, B, and C Helicopters
Sikorsky Aircraft Corporation Model S-76 A, B, and C Helicopters
Model S-76 A, B, and C helicopters, with a dual channel autopilot and with dual inverters installed, certificated in any category. Note: The following serial-numbered helicopters were manufactured with the dual channel autopilots and dual inverters installed: S-76 A Serial Numbers: 760267, 760268, 760270 through 760298, 760300 through 760302, 760304 through 760309, 760364, 760366, 760369 through 760371, 760373 through 760378; S-76 B Serial Numbers: 760262, 760269, 760299, 760303, 760310 through 760363, 760365, 760367, 760368, 760372, 760379 through 760382, 760387, 760391, 760393, 760395, 760399, 760403, 760404, 760409, 760410, 760413, 760414, 760416, 760425, 760427 through 760430, 762976 (760433), 760437, 760439, 760441 through 760445, 760447 through 760452, 760454, 760455, 760458, 760462, 760465, and 760507; and S-76 C Serial Numbers: 760383 through 760386, 760388 through 760390, 760392, 760394, 760396 through 760398, 760400 through 760402, 760405 through 760408, 760411, 760412, 760415, 760417 through 760424, 760426, 760431, 760432, 760434 through 760436, 760438, 760440, 760446, 760453, 760456, 760457, 760459 through 760461, 760463, 760464, 760466 through 760506, and 760508 through 760526.
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.
