Aerospatiale AS355 N708AC accident near Rifle, Colorado

Probable cause

A loss of tail rotor effectiveness, the pilot’s subsequent loss of helicopter control, and collision with terrain.

NTSB analysis

The pilot of the helicopter was maneuvering at a low altitude to conduct his first aerial observation flight of the day. The passenger, who was a camera operator for the flight, reported that the pilot began a hover over the electrical substation while they discussed a plan for the flight. While in a low altitude hover, the helicopter began swaying left and right, then spinning in a counterclockwise (left) direction. Shortly thereafter, the helicopter impacted the terrain. The pilot had no recollection of the accident. Witness observations indicated that the helicopter’s final impact was immediately followed by a postcrash fire that destroyed the helicopter. Postaccident examination of the helicopter and engine revealed no evidence of mechanical anomalies that would have precluded normal operation.

The helicopter was operating at a gross weight of 5,040 lbs, and the maximum allowable gross weight is 5,291 lbs. The calculated density altitude was 6,566 ft mean sea level. The accident helicopter’s flight characteristics at the time of the accident would have included slow airspeed, a high-power setting, that were all conducive to a loss of tail rotor effectiveness (LTE), thus it is likely that the loss of control was the direct result of LTE.

Text from the NTSB. Open the NTSB docket for CEN20LA273 for the full record.