Robinson Helicopter Company R22 N712U accident near Alta, Utah

Probable cause

The flight instructor's decision to follow a route over mountainous terrain in conditions that exceeded the helicopter’s ability to maintain terrain clearance.

NTSB analysis

The flight instructor reported that the outbound training flight on the morning of the accident followed roads through mountain passes. For the return flight, the flight instructor decided to take a more direct route and fly over 11,000-foot-high mountainous peaks. The pilot undergoing instruction was controlling the helicopter during the climb, which was uneventful. As the helicopter crested the peak, the pilot initiated a descent and then began to raise the collective to reduce the descent rate; however, as he did so, the rotor speed began to decay, and the low rotor rpm warning sounded. The flight instructor took over the flight controls but was unable to arrest the descent, and he subsequently chose to perform a forced landing to rocky terrain. The helicopter struck the ground, tumbled, and was destroyed; both occupants sustained serious injuries.

The helicopter was operating at a density altitude equal to or just above the helicopter's maximum operating density altitude of 14,000 feet. At the altitude of the accident site, the helicopter was not capable of hovering in-ground-effect; therefore, it was unlikely that a landing could have been successfully accomplished in the rocky terrain. Further, after cresting the peak, the helicopter likely encountered downdrafts due to the mountainous terrain surrounding the accident site, which further degraded the helicopter's performance. A postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.

Text from the NTSB. Open the NTSB docket for WPR13LA315 for the full record.