Sikorsky S-76C++ crash near 77 nm south east of Lagos, Lagos, Nigeria

On the outbound leg from Lagos to the Erha floating production storage and offloading vessel the captain noticed an unusual vibration, and about fifteen minutes later the digital automatic flight control system and trim fail captions illuminated twice and the number one autopilot decoupled on both occasions. A passenger reported a burning smell. The crew continued and landed, and visual checks on the deck found nothing. On the return leg with eleven on board the trim fail and flight control system captions came up repeatedly again. The pilot flying reported the collective heavy and the autopilot decoupling, there was a high rate of descent, and the compass was unreliable. The captain declared a mayday about 66 nautical miles from Lagos, stabilised at 1,500 feet, briefed the passengers and ditched under control at 05 45 43 N 004 13 54 E. All eleven were taken off with minor injuries. The causal factor was that the crew had selected the compass to free directional gyro mode for the helideck landing and had not returned it to slave mode after departure, so unsynchronised heading inputs kept cutting the trim and disengaging the autopilot. Non-adherence to the after take-off checks and the failure to disengage the autopilot and fly manually were contributory.