NTSB Identification: DEN07CA013.
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Accident occurred Monday, October 16, 2006 in Monticello, UT
Probable Cause Approval Date: 01/31/2007
Aircraft: Robinson R22 BETA, registration: N224VR
Injuries: 1 Uninjured.
NTSB investigators used data provided by various entities, including, but not limited to, the Federal Aviation Administration and/or the operator and did not travel in support of this investigation to prepare this aircraft accident report.
The pilot said 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." He 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. Main and tail rotor and tail rotor blades struck the trees, separating the tail rotor blades and gearbox from the tail boom. According to the helicopter manufacturer, nothing was found that would explain the oscillations described by the pilot, or why the low-rotor RPM horn/light activated.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: an airframe vibration for reasons undetermined, resulting in the pilot performing a precautionary landing, and obstacle clearance not possible. Full narrative available
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