NTSB Identification: NYC06LA062.
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Accident occurred Friday, February 17, 2006 in Big Creek, KY
Probable Cause Approval Date: 06/30/2008
Aircraft: Bell 206B, registration: N36HF
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 of the helicopter was en route to pick up passengers, when approximately 16 miles prior to his intended destination, he landed in a field due to deteriorating weather conditions. During a cellular telephone conversation with his employer, it was decided that the pilot should reverse course, land at a nearby airport, or return to the helicopter's base. The pilot took off from the field and attempted to fly directly to an airport, but was again unable to follow his desired course due to weather. As he maneuvered, the weather improved, the ridgelines were visible, and the pilot was able to fly "about 100 feet above the trees, and 200 feet below the clouds" as he approached a field that was crossed by a power line. The pilot said he chose to land in the field because of a "klunking" noise behind him. "As I entered the approach the noise got worse and the aircraft started to vibrate. The vibrations got very bad as I tried to arrest my descent, so I decided that touching down hard was better than shaking apart." Examination of the global positioning system ground track revealed that the helicopter descended at a rate of 1,000 feet per minute during an s-turn across the face of a mountain before it leveled over flat terrain, and slowed below effective translational lift, in the vicinity of the crash site. The crash site was surrounded by rising terrain, in the lee of a mountain with strong winds, and an AIRMET for turbulence was in effect along the route of flight. The helicopter experienced a high sink rate and high levels of vibration prior to ground contact. According to The Good Aviation Practices publication Helicopter Performance, published by the Civil Aviation Authority of New Zealand (November 2002), "Local terrain, trees, and buildings all influence the flow of wind near them. The mechanical turbulence resulting from this disturbed airflow may become very marked in the lee of the obstruction. A gusting wind situation where windshear is likely to be present will require a greater power margin to deal with any unexpected loss of airspeed and sink." Examination of the wreckage and a post accident engine run revealed no preimpact anomalies.

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

The pilot's inadvertent settling with power during a descent. Contributing to the accident was mechanical turbulence in the lee of an obstruction in windy conditions.

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