NTSB Identification: FTW02LA177.
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Accident occurred Saturday, June 08, 2002 in Nederland, CO
Probable Cause Approval Date: 04/01/2003
Aircraft: Bell 47G-3B-1, registration: N999DW
Injuries: 1 Uninjured.

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

Prior to the flight in mountainous terrain, the pilot obtained a weather forecast that called for winds from the southwest at 30 mph, with gusts up to 40 mph. The flight departed and was in cruise flight at 9,000 feet (700 feet agl) with a 20-25 knot headwind and experiencing light turbulence, when the flight encountered "severe turbulence." The pilot stated that the helicopter went "up and down violently for a period of 2-3 seconds." The tailrotor drive shaft was severed by the main rotor blades, and the helicopter then experienced "a right yaw that full application of left pedal would not correct." The pilot stated that during the event the engine and rotor rpm increased past their upper limits. He was able to bring the engine and rotor rpm within limits and regained control of the helicopter. Subsequently, the pilot performed an autorotation to sloping terrain without further incident. According to a witness, who was fishing on a lake 4 miles from the accident site, he observed water spouts between 2 and 8 feet tall and high swirling winds near the time of the accident.

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

the pilot's inadvertent in-flight encounter with severe turbulence, which resulted in main rotor-tailboom contact and the separation of the tailrotor drive shaft.

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