NTSB Factual Report

On October 16, 2006, approximately 1210 mountain daylight time, a Robinson R22BETA, N224VR, registered to and piloted by an airline transport certificated pilot, was substantially damaged when the helicopter struck some scrub trees and terrain following uncontrollable yaw oscillations while in cruise flight approximately 18 miles northeast of Monticello, Utah. Visual meteorological conditions prevailed at the time of the accident. The business flight was being conducted under the provisions of Title 14 CFR Part 91 without a flight plan. The pilot, the sole occupant aboard, was not injured. The local flight originated at Dove Creek, Colorado, approximately 1150, and was en route to Lisbon Valley, Utah.

According to the pilot's accident report and a verbal statement he gave to an FAA inspector, he was cruising at 8,500 feet msl (mean sea level) and at 65 KIAS (knots indicated airspeed) when he experienced a "slight yaw oscillation." The pilot decided to make a precautionary landing and initiated a descent. The oscillations increased to about one yaw per second. Before reaching the selected landing site, the "low-rotor RPM horn/light activated. When the pilot lowered the collective control to recover, he got an engine and rotor overspeed indication of 110 per cent. The pilot made a 180-degree turn and autorotated from 800 feet agl. The helicopter landed on rocky terrain, surrounded by pinon and juniper trees. Post-accident examination revealed the main rotor and tail rotor blades had struck trees. The tail rotor blades and gearbox separated from the tail boom.

According to a Robinson Helicopters repairman, he had found nothing that would explain the oscillations described by the pilot, or why the low-rotor RPM horn/light activated.

NTSB Probable Cause

an airframe vibration for reasons undetermined, resulting in the pilot performing a precautionary landing, and obstacle clearance not possible.