NTSB Identification: FTW03LA011.
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Accident occurred Saturday, October 12, 2002 in Vinson, OK
Probable Cause Approval Date: 11/25/2003
Aircraft: Brantly Helicopter B-2B, registration: N9008H
Injuries: 2 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.
After the helicopter leveled off at 2,500 feet, scattered clouds began moving in. The pilot climbed to 4,500 feet where clouds were now above and below him, preventing the pilot from locating his next checkpoint until there were breaks in the clouds. Approximately 56 miles into the flight and with the clouds thinning, the helicopter broke into a right turn. After turning back on course the helicopter began gaining altitude, then nosed over quickly, dropping approximately 1,000 feet. After leveling off back on course, the helicopter began gaining altitude again to 5,000 feet and began a smooth left-hand descending turn into a canyon. All attempted control inputs by the pilot were unresponsive. The helicopter was now traveling at a high rate of speed through the canyon, eventually coming to a quick stop to the right on a hill at the end of the canyon. As rotor rpm bled off the pilot attempted another control input by applying aft cyclic and left rudder pedal; however, the helicopter would not respond. The helicopter impacted terrain in a rapid spin to the left, coming to rest on its left side. Post-accident examination of the helicopter's flight controls revealed no anomalies which would have prevented normal operations. Approximately two hours prior to departure, a warm front was moving into the area of intended flight. At the time of the accident, weather observation facilities in the region reported winds gusting up to 31 knots with multilayered clouds.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot's inadvertent flight into adverse weather conditions during cruise resulting in his failure to maintain control of the helicopter, and his failure to maintain rotor rpm. Contributing factors relating to the accident included the frontal activity associated with the adverse weather condition and the variable wind.
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