NTSB Identification: SEA08LA213
14 CFR Part 91: General Aviation
Accident occurred Saturday, September 27, 2008 in Jelm, WY
Probable Cause Approval Date: 03/23/2009
Aircraft: BELL 206B, registration: N59611
Injuries: 1 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot reported that he was flying over his ranch property at about 50 knots looking for stray cattle when "...a strong tailwind or twister caused the ship to vibrate very fast and violent, and dove to the right." The pilot stated that several people on the ground observed the helicopter spin 5 to 6 times before impacting the uneven and sloping ground and rolling over. The pilot further stated, "I couldn't get response from the tail rotor, collective, or cyclic." The ranch foreman saw the helicopter making a "big circle," followed by 3 or 4 "tight circles" in a clockwise direction before impacting terrain. A post crash examination of the helicopter by a Federal Aviation Administration (FAA) aviation safety inspector revealed no apparent malfunctions. The pilot reported no preimpact anomalies with the helicopter. The Rotorcraft Flying Handbook states that a loss of tail rotor effectiveness (LTE) is the occurrence of an uncommanded yaw rate that does not subside on its own accord, which can result in the loss of helicopter control. The recovery technique for LTE is full left pedal while simultaneously moving cyclic control forward to increase airspeed. If altitude permits, reduce power. FAA Advisory Circular 90-95 states, "Any maneuver which requires the pilot to operate in a high-power, low-airspeed environment with a left crosswind or tailwind creates an environment where unanticipated right yaw may occur."

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The pilot's encounter with a loss of tail rotor effectiveness event and his failure to maintain directional control while maneuvering. Contributing to the accident were the tailwind condition and the sloping, uneven terrain.

Full narrative available

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