On September 29, 2004, about 0615 central daylight time, a Bell 206L helicopter, N34CA, registered to and operated by Panther Helicopters Inc., as a Title 14 CFR part 135 on demand air taxi flight, ditched into the Gulf of Mexico. Visual meteorological conditions prevailed, and a company visual flight rules flight plan was filed. The airline transport-rated pilot and two passengers were not injured, and the helicopter sank in the Gulf of Mexico, and was not recovered. The flight originated in Belle Chasse, Louisiana, the same day, about 0508. The pilot stated that the hour-long flight from Belle Chasse, Louisiana, to Viosca Knoll oil platform No. VK817, had initially been uneventful. He further stated that at a distance of approximately 2 miles from the platform, he started a descent from his cruising altitude of 1,000 feet. During the final approach, when within about 300 to 400 yards, he said he increased collective input to control the rate of descent, but the engine failed to respond normally. As collective input was increased, he said the rpms decreased and did not recover. He said he stopped applying collective to prevent the rpms from decreasing below 90 percent, and further stated that he noted no other adverse indications. He said the rate of descent increased, and he applied the remaining collective pitch input to arrest the rate of descent, just prior to impacting the water. The helicopter impacted the water with "normal forces", and the pilot said he tried twice to inflate the floats, but both attempts were unsuccessful. During the ditching, the helicopter had impacted the surface of the water with a slight movement to the left front, and the main rotor on the left side impacted the water. The pilot said that he and both passengers exited the helicopter, and it sank in about 600 feet of water. Personnel from a nearby boat recovered the pilot and passengers from the Gulf of Mexico, and transported them to the oil platform. The passenger who was seated in the front left seat, said that when the helicopter was about 300 yards from the platform, it "started going down" and attempts by the pilot to "lift" the helicopter were unsuccessful. He further stated that he did not notice anything unusual with the helicopter during the flight, until it was located within 300 yards of the platform, when heard no sounds associated with the main rotor blades impacting the water. He said the pilot tried three separate times to deploy the floats, but all attempts were unsuccessful.