What happened
During a lift-off from an oil platform located in the Gulf of Mexico, the helicopter began performing a slow, uncommanded left turn. In an attempt to correct the deviation, the pilot attempted to fly the aircraft by increasing collective and lowering the nose. Following two turns, the aircraft settled and impacted the water in a nose-down attitude with a left bank. At the time of the impact, the floats had not been inflated and the autopilot remained connected.
The investigation
Investigators found no evidence of mechanical failure occurring prior to the impact. However, interviews indicated that the aircraft had not been stabilized in a hover before the takeoff was initiated. A review of maintenance records revealed a previous write-up noting that the aircraft required more right pedal than usual during forward flight and in a hover.
In response to this reported issue, a mechanic had performed an adjustment on a tube that runs rearward from the pedal assembly to the lower portion of the autopilot system. According to the maintenance manual, this tube is classified as one of the "semi-fixed" rods. The manual specifically cautions that these rods are adjusted only once when they are fitted to the aircraft and must not be adjusted subsequently.