Incident Overview
A helicopter pilot reported that while on approach to an oil platform, approximately 300 to 400 yards from the platform, the engine did not respond normally when he increased collective input to control the rate of descent. As collective was increased, the rotor rpm decreased and did not recover. The pilot ceased collective application to prevent rotor rpm from falling below 90 percent.
Pilot Actions
According to the pilot, no other adverse indications were observed. The rate of descent increased, and he applied the remaining collective pitch input just before impacting the water to arrest the descent rate. After impact, the pilot attempted to inflate the floats twice, but both attempts were unsuccessful.
Post-Impact Events
The pilot and both passengers exited the helicopter. The helicopter sank in approximately 600 feet of water and was not recovered.