NTSB Identification: DFW07GA119
14 CFR Public Use
Accident occurred Tuesday, May 22, 2007 in San Elizario, TX
Probable Cause Approval Date: 12/28/2008
Aircraft: EUROCOPTER AS 350 B3, registration: N851BP
Injuries: 1 Fatal,1 Serious.

: NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this public aircraft accident report.

The helicopter was reported to have been maneuvering at a low airspeed at an altitude of approximately 150 feet above the ground while on a patrol flight near an international border. Local authorities reported that the helicopter impacted a parked pickup truck in a nose-low attitude while in a right turn, coming to rest on its right side. Witnesses said that the helicopter "appeared to dip the nose-down and enter a spin to the right nearly straight down. One witness added that the helicopter appeared to have recovered from the spin and initiated a climb before it began to spin to the right again, impacting the ground in a near-vertical attitude. Other witnesses added that the engine appeared to be "screaming." A witness, who reported having experience as a helicopter mechanic, added that the engine was screaming, but that the rotor system sounded as though it was slowing down. One witness stated it sounded like it was sucking or chopping air. The recorded weather near the accident site was reported as winds from 260 degrees at 12 knots, visibility 10 statute miles, clear skies, temperature 23 degrees Celsius, dew point 1 degree Celsius, and a barometric pressure of 29.94 inches of Mercury. Density Altitude was computed to be 5,433 feet MSL, No discrepancies or pre-existing anomalies were found with the helicopter or the engine that could have precluded normal flight. A performance study was conducted to determine the controllability and maneuvering capabilities while operating in the flight environment during the assigned observation mission. The study concluded that at the approximate altitude of 150 feet AGL and an airspeed of 20-30 knots, may not have allowed sufficient time or altitude for the pilot to recover after the helicopter entered a vortex ring state, A fully developed vortex ring state is characterized by an unstable condition where the helicopter experiences uncommanded pitch and roll oscillations, has little or no cyclic authority, and achieves a descent rate which, if allowed to develop, may approach 6000 feet per minute. A vortex ring state may be entered during any maneuver that places the main rotor in a condition of high upflow and low forward airspeed

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

The pilot's encounter with a vortex ring state and his inability to maintain control of the helicopter.

Full narrative available

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