Primary finding
Probable cause
The student pilot's failure to maintain translational lift airspeed while approaching the pinnacle and the certificated flight instructor's delayed remedial action and inadequate supervision of the flight.
Investigator assessment
Analysis narrative
The purpose of the instructional flight was to practice pinnacle approaches. Approaching a ridgeline to be used for the pinnacle approach, the flight instructor observed the airspeed drop below 41 knots (translational lift), resulting in a loss of altitude and the inability to clear the ridgeline. The flight instructor took control of the helicopter, initiated a left turn to avoid the ridgeline, and lowered collective in an attempt to gain airspeed. The helicopter subsequently impacted terrain in a level attitude after failing to gain sufficient altitude to clear a ravine, sliding about 30 to 40 feet after impact. The instructor said there were no preimpact anomalies with the airframe or engine during the flight.
Source record
Factual narrative
The purpose of the instructional flight was to practice pinnacle approaches. Approaching a ridgeline to be used for the pinnacle approach, the flight instructor observed the airspeed drop below 41 knots (translational lift), resulting in a loss of altitude and the inability to clear the ridgeline. The flight instructor took control of the helicopter, initiated a left turn to avoid the ridgeline, and lowered collective in an attempt to gain airspeed. The helicopter subsequently impacted terrain in a level attitude after failing to gain sufficient altitude to clear a ravine, sliding about 30 to 40 feet after impact. The instructor said there were no preimpact anomalies with the airframe or engine during the flight.