Accident Narrative
A helicopter began its lift-off from an oil platform in the Gulf of Mexico. Shortly after becoming airborne, the helicopter initiated a slow left turn that was not commanded by the pilot. The pilot attempted to regain control by lowering the aircraft's nose and increasing collective pitch. After completing two full turns, the helicopter settled and struck the water in a left bank, nose-down attitude. During the sequence, the autopilot remained engaged and the flotation devices were not deployed. Examination of the wreckage revealed no pre-impact mechanical failure.
Maintenance History
Prior to the accident, a maintenance log entry reported that the aircraft required more right pedal input than usual during hover and forward flight. In response, a mechanic adjusted a tube that runs from the pedal assembly rearward to the lower portion of the autopilot system. The maintenance manual identifies this tube as one of the "semi-fixed" rods and specifically cautions that such rods are adjusted only once when initially fitted to the aircraft and must not be adjusted thereafter.
Pilot Actions and Hover Stability
Interviews indicated that the helicopter was not stabilized in a hover before the takeoff was initiated. The pilot's inputs of lowering the nose and increasing collective did not arrest the uncommanded turn.