What happened
While attempting to land at an offshore oil rig, the pilot in command allowed the helicopter to drift, resulting in the right main gear landing on the safety apron rather than the platform. Following two unsuccessful attempts to reposition the aircraft, the pilot decided to take off and attempt the landing again.
During the subsequent takeoff from a hover, the pilot applied increased collective. The aircraft responded by turning to the right around its vertical axis. Interpreting this right turn as a loss of directional control, the co-pilot reduced both engines to ground idle by moving the speed levers. This action was performed without any announcement or coordination with the pilot in command.
As a result of the engine power reduction, the main rotor blades struck the platform. The aircraft then underwent an uncontrolled descent into the water. All occupants were not injured.