N51727Enstrom F-28C · 1977

On February 20, 2012, about 1030 mountain standard time, an Enstrom F-28C helicopter, N51727, was substantially damaged following a loss of engine power and impact with terrain at the Kalispell City Airport (S27), Kalispell, Montana. The certified flight instructor and pilot receiving instruction were not injured. Visual meteorological conditions prevailed for the local instructional flight, which was being operated in accordance with 14 Code of Federal Regulations (CFR) Part 91, and a flight plan was not filed. The flight departed S27 about 0940.

In a statement provided to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the certified flight instructor reported that on the fourth practice autorotation of the morning, the student initiated a 180-degree autorotation from about 650 feet above ground level (agl). The instructor stated that at the 90-degree point he recognized that the engine had failed, at which time he took full control of the helicopter and initiated an [emergency descent]. After touching down at a speed of about 20 knots, the helicopter slid lightly forward before becoming airborne, then did a 180-degree rotation [to the left] and landed on the taxiway with the main rotor spinning down. The helicopter sustained substantial damage to the last 3 feet of the tail section, with the tail rotor having been severed by the main rotor blades.

On February 22, 2012, under the supervision of a Federal Aviation Administration (FAA) aviation safety inspector, the accident flight instructor started the engine with the aid of the fuel boost pump; the engine started immediately. Subsequently, the engine ran smoothly from idle to low power from about 1,300 to 2,000 rpm, with no discrepancies noted. The inspector concluded his inspection by noting that a review of the helicopter’s maintenance records revealed no discrepancies in either the airframe or engine logbooks. The most recent annual inspection was performed on February 10, 2012. The inspector’s 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.

At 1055, the automated weather observing system at GPI, which was located about 7 nautical miles northeast of the S27, reported wind 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 (F), dew point 27 degrees F, and an altimeter setting of 29.87 inches of mercury.

A review of the Carburetor Icing chart revealed that the temperature/dew point spread indicates "Serious icing at glide power” and “Icing at glide and cruise power.”