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The Helicopter's Airframe Engine Inlet Area Was Not Equipped With A Particle Separator Or Snow Baffles
The helicopter was departing on a 14 CFR Part 135 sightseeing flight over the Grand Canyon when it experienced a loss of engine power during the takeoff initial climb. The helicopter then collided with the ground as the pilot tried to avoid wires during the autorotative descent. The pilot said that the start, warm-up, and takeoff were normal. As the helicopter climbed through 200 feet, he heard a bang and sensed a total loss of power; he then entered an autorotation to a clear ramp area of the airport.
The pilot said that during the descent he had "to pull some pitch to miss some electric wires," and then the helicopter hit hard on the ramp. Several witnesses with helicopter experience said the helicopter was about 75-100 feet in the air when the engine lost power. One witness saw a white puff of smoke emanate from the exhaust nozzle and then heard silence. An experienced helicopter pilot saw the accident pilot stretch his autorotative glide to miss wires that were right in his path and then hit hard and flat at the end of the autorotation. The pilot who flew the accident helicopter the day before the mishap parked the helicopter in front of the terminal building, facing west-northwest at the end of the day, and did not install the engine inlet or exhaust covers.
This was the first flight of the day for the accident helicopter. Another company pilot had been awake from 0500 and saw snow falling until about 0700. He and the accident pilot used brooms, squeegees, and brushes to clean the snow off the helicopters during their preflights. He said that about 75 percent of his preflight time was spent in removing the accumulated snow and ice off his helicopter, principally from the upper deck, roof, and doghouse. He noted that about 1/8-inch of snow had accumulated on the upper surfaces of his aircraft. The witness stated that he found and removed "less than a handful of snow from the engine intakes." He watched the accident pilot on a step ladder brushing snow off the top of his helicopter. He said that neither his nor the accident pilot's helicopters had the intake or exhaust covers installed while they were parked overnight on the ramp.
Official weather records from the National Weather Service show that blowing snow conditions occurred periodically during the late night of April 17 and early morning hours of April 18, with 0.24 inches of snowfall recorded. The winds were generally from the west-southwest during this period at velocities up to 16 knots. The engine was not equipped with an auto reignition system. The helicopter's airframe engine inlet area was not equipped with 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 can induce a flameout in the Allison 250 series commercial engines.
The first impact point was found 56 feet from a 50-foot-high power line strung between light poles, which bordered the crash site. During extensive examinations of the wreckage, no preimpact mechanical malfunctions or failures were found to any control system, or to any component related to the ability of the engine to produce power and deliver it to the rotors. Clear fuel was found in the fuel lines and filters, and, all fuel and pneumatic line B-nut fittings and connections were tight. When electrical power was connected, both boost pumps operated and pumped fuel. Following examination of the engine in the wreckage, it 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. At the takeoff power test point, the engine was 0.6-percent (4 horsepower) below the minimum limit. In his written statement, which was composed 29 days after the accident, the accident pilot said that during his preflight he "checked the inlets very thoroughly for any snow" and found none.
The pilot observed that following removal of the snow and ice from the airframe, the helicopter sat "in the sun warming for a good 30 minutes before flight." NWS records show that the temperature at the time of the accident was 3 degrees C.
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Helicopter Accident Newsroom