Bell 206B N59611 accident near Woods Landing-Jelm, Wyoming

Probable cause

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.

NTSB analysis

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."

Text from the NTSB. Open the NTSB docket for SEA08LA213 for the full record.