Accident Details
On February 20, 2012, at about 1030 mountain standard time, an Enstrom F-28C helicopter, registration N51727, sustained substantial damage after experiencing a loss of engine power and impacting terrain at Kalispell City Airport (S27) in Kalispell, Montana. The helicopter was engaged in a local instructional flight under 14 Code of Federal Regulations Part 91, with a certified flight instructor and a pilot receiving instruction on board. Both occupants were not injured. The flight departed S27 at approximately 0940 and was conducted in visual meteorological conditions; no flight plan was filed.
The instructor reported that during the fourth practice autorotation of the morning, the student initiated a 180-degree autorotation from about 650 feet above ground level. At the 90-degree point, the instructor recognized that the engine had failed and took full control, initiating an emergency descent. After touching down at about 20 knots, the helicopter slid forward, became airborne briefly, rotated 180 degrees to the left, and landed on a taxiway with the main rotor spinning down. The helicopter sustained substantial damage to the last three feet of the tail section, and the tail rotor was severed by the main rotor blades.
Investigation
On February 22, 2012, a Federal Aviation Administration (FAA) aviation safety inspector supervised the accident flight instructor in starting the engine with the fuel boost pump. The engine started immediately and ran smoothly from idle to low power between 1,300 and 2,000 rpm, with no discrepancies. The inspector reviewed the helicopter's maintenance records and found no discrepancies in either the airframe or engine logbooks. The most recent annual inspection had been performed on February 10, 2012. The examination failed to reveal any anomalies with the engine or airframe that would have precluded normal operation. The reason for the loss of engine power could not be determined.
Weather Conditions
At 1055, the automated weather observing system at Glacier Park International Airport (GPI), about 7 nautical miles northeast of S27, reported wind from 150 degrees at 9 knots, visibility 10 miles, scattered clouds at 2,400 feet, broken clouds at 2,800 feet, overcast clouds at 5,500 feet, temperature 32 degrees Fahrenheit, dew point 27 degrees Fahrenheit, and an altimeter setting of 29.87 inches of mercury. A review of the Carburetor Icing chart indicated that the temperature/dew point spread corresponded to "Serious icing at glide power" and "Icing at glide and cruise power."