On February 23, 1994, about 1613 hours Hawaii standard time, an Aerospatiale AS350-B helicopter, N766MP, collided with the terrain at 10,500 feet mean sea level (msl) about 3 miles north of Humuula, Hawaii. The pilot was conducting a visual flight rules (VFR) sightseeing flight to the Volcanoes National Park, under Title 14 CFR Part 135. The helicopter, operated by Papillon Hawaiian Helicopters, Honolulu, Hawaii, received substantial damage. The certificated commercial pilot and four passengers were not injured; the remaining two passengers sustained serious injuries. Instrument meteorological conditions prevailed. The company provided flight following and the pilot filed a company VFR flight plan. The flight originated from Waikoloa about 1500 hours. The pilot reported in the National Transportation Safety Board Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1/2, that after departure the flight went southeast toward the Kilauea Volcano. The route of flight is through a high mountain pass between Mauna Kea and Mauna Loa. The pilot said that low clouds prevented him from proceeding with the planned flight. He began maneuvering around the clouds that were forming in the pass. While maneuvering, the pilot climbed the helicopter through 10,500 feet msl and encountered a downdraft. The pilot attempted to turn away from the mountain toward the east, but without success. He said that the helicopter lacked sufficient power to prevent it from "...hitting the mountain...." The pilot said that after the helicopter came to rest, he shut off the engine. He also said that the helicopter did not experience any mechanical difficulties before colliding with the terrain. The operator provided the Safety Board with the accident flight manifest and fueling records. The flight's weight prior to takeoff was 4,279 pounds -- 21 pounds under the maximum allowable gross weight. The temperature near the accident area at sea level was 76 degrees Fahrenheit. Safety Board investigators used the standard adiabatic lapse rate of 3.5 degrees/1,000 feet and found the temperature at the accident site was 39 degrees Fahrenheit (3.8 degrees Celsius). According to the flight manual, the fuel consumption rate is about 42 gallons/hour. Safety Board investigators calculated the helicopter's weight at the time of accident and found it to be about 3,941 pounds. Safety Board investigators contacted Mr. Del Livingston, American Eurocopter, Dallas, Texas, and requested and received performance data for the accident helicopter. Mr. Livingston said that he had reviewed the performance data charts for the accident helicopter. His review revealed that based on the helicopter's flight parameters, it could not hover in or out of ground effect. The helicopter could have maintained a rate of climb of about 700 feet/minute if flown straight ahead at Vy (best rate of climb speed - 55 knots) and at maximum continuous power. He also said that when the pilot turned the helicopter, and if he was below Vy and entered a downdraft, the power required to conduct this maneuver would have exceeded the available power. Safety Board investigators review of the performance data confirmed Mr. Livingston's determination of the hover in or out of ground effect and its rate of climb capability.