Accident Narrative
The helicopter departed on a 22-nautical-mile training flight with 10 gallons of fuel in its 28-gallon tank. During the flight, both the certified flight instructor (CFI) and the student pilot observed that an unusually high application of carburetor heat was necessary to keep the inlet temperature needle within normal limits. The student pilot, intending to enter the traffic pattern at the destination airport, initiated a descent and maneuvered the helicopter into a right turn. At approximately 500 feet above ground level (agl), the engine experienced a momentary power interruption and then stopped completely.
The student pilot performed an autorotation, and the helicopter touched down in a crop field. The right skid dug into the soft, muddy ground, causing the helicopter to rotate around the skid and come to rest on its right side.
Technical Findings
Prior to the accident, the fuel tank contained about 5 gallons of fuel. Due to the orientation of the fuel outlet port inside the tank, the helicopter is susceptible to unporting when low quantities of fuel are present during maneuvers. The outlet is located on the left side of the tank; during a right turn with minimal fuel, the outlet can intake air, resulting in fuel starvation to the engine.
According to a standard reference icing probability chart, the atmospheric conditions at the time of the accident were in the range considered favorable for carburetor ice formation.