Primary finding
Probable cause
The certified flight instructor's inadequate supervision of the practice autorotation. Contributing factors included the terrain drop off and the failure of the pilot undergoing instruction to maintain adequate rotor rpm.
Investigator assessment
Analysis narrative
The certified flight instructor (CFI) and private pilot undergoing instruction were conducting 180-degree autorotations in a helicopter. The accident happened on the third autorotation. The CFI stated that the entry and glide into the autorotation were uneventful. During the flare portion, sufficient rotor revolutions per minute (rpm) were not produced, and the low rotor rpm light and horn activated. The helicopter was leveled and a run on landing was performed. According to the CFI, the helicopter was not over the intended hard surface for landing. During the attempted run on landing, the helicopter ran over a 3-foot drop off and came to rest on its left side. The CFI did not report any mechanical malfunctions. The temperature at the time of the accident was reported as 39 degrees Celsius.
Source record
Factual narrative
The certified flight instructor (CFI) and private pilot undergoing instruction were conducting 180-degree autorotations in a helicopter. The accident happened on the third autorotation. The CFI stated that the entry and glide into the autorotation were uneventful. During the flare portion, sufficient rotor revolutions per minute (rpm) were not produced, and the low rotor rpm light and horn activated. The helicopter was leveled and a run on landing was performed. According to the CFI, the helicopter was not over the intended hard surface for landing. During the attempted run on landing, the helicopter ran over a 3-foot drop off and came to rest on its left side. The CFI did not report any mechanical malfunctions. The temperature at the time of the accident was reported as 39 degrees Celsius.