Accident Narrative
A helicopter conducting a 14 CFR Part 135 sightseeing flight over the Grand Canyon experienced a loss of engine power during the takeoff initial climb. The pilot reported that the start, warm-up, and takeoff were normal. As the helicopter climbed through 200 feet, a bang was heard and a total loss of power was sensed. The pilot entered an autorotation toward a clear ramp area of the airport. During the descent, the pilot had to increase pitch to miss electric wires, and the helicopter impacted the ground hard on the ramp.
Witness Observations
Several witnesses with helicopter experience reported that the helicopter was about 75 to 100 feet above ground when the engine lost power. One witness observed a white puff of smoke emanating from the exhaust nozzle, followed by silence. Another experienced helicopter pilot saw the accident pilot stretch the autorotative glide to avoid wires directly in the path, then hit the ground hard and flat at the end of the autorotation.
Preflight and Weather Conditions
The helicopter had been parked overnight in front of the terminal building, facing west-northwest, without engine inlet or exhaust covers installed. This was the first flight of the day. A company pilot who had been awake since 0500 reported snow falling until about 0700. Both pilots used brooms, squeegees, and brushes to clean snow off their helicopters during preflights. The witness noted that about 75 percent of his preflight time was spent removing snow and ice from the upper deck, roof, and doghouse, with about 1/8 inch of snow accumulated on upper surfaces. He found and removed less than a handful of snow from the engine intakes of his own helicopter and observed the accident pilot brushing snow off the top of his helicopter. Neither helicopter had intake or exhaust covers while parked overnight. Official weather records from the National Weather Service indicated blowing snow conditions periodically during the late night of April 17 and early morning of April 18, with 0.24 inches of snowfall recorded. Winds were generally from the west-southwest at velocities up to 16 knots. The temperature at the time of the accident was 3°C. The accident pilot stated 29 days after the accident that during his preflight he checked the inlets thoroughly and found no snow, and that after snow removal the helicopter sat in the sun warming for about 30 minutes before flight.
Engine Examination
The helicopter's engine was not equipped with an auto reignition system, and the airframe engine inlet area lacked a particle separator or snow baffles. According to Rolls Royce Allison, testing performed in 1968 showed that as little as 30 grams of snow/slush (25 percent water) ingested in the engine inlet could induce a flameout in Allison 250 series commercial engines. The first impact point was found 56 feet from a 50-foot-high power line strung between light poles bordering the crash site. Extensive examinations of the wreckage revealed no preimpact mechanical malfunctions or failures to any control system or component related to engine power production and delivery to the rotors. Clear fuel was found in the fuel lines and filters, and all fuel and pneumatic line B-nut fittings were tight. When electrical power was connected, both boost pumps operated and pumped fuel. The engine was removed from the helicopter and installed in a test cell for a run in an as-removed condition. The engine exceeded new engine minimum horsepower limits for a 250-C30P at all test points except for takeoff power, where it was 0.6 percent (4 horsepower) below the minimum limit.