IAD01FA089 · Bell 206B

The purpose of the helicopter flight was to take aerial photographs of a large airport expansion construction project. The helicopter approached the construction site in an out-of-ground-effect hover taxi, with a quartering left tailwind. The helicopter turned to the right, and slowed to a stationary hover about 250 feet above the ground with a direct tailwind. Once in a hover, the helicopter made a right, rapid 180-degree pedal turn around the mast, stopped momentarily, then initiated another rapid pedal turn to the right. The helicopter turned at a faster rate than the initial turn, and continued into a spinning, vertical descent to the ground. Examination of the helicopter revealed no mechanical anomalies. The collective was in the full up position, and the main rotor blades exhibited signatures consistent with low rotor rpm at ground contact. A review of the pilot's company flight records revealed he had 531 hours of total flight experience, 60 hours of which were in airplanes. The pilot had 87 hours of experience in make and model. A relative wind chart published by the manufacturer depicts a helicopter facing 360 degrees over a compass rose. One shaded area of the chart depicts winds from between 120 degrees and 240 degrees, at wind speeds above 5 knots and up to 17 knots. According to a note on the chart an unanticipated right yaw may occur when operating in the shaded areas of the chart. According to FAA Advisory Circular (AC) 90-95, "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." The AC also advised of greater susceptibility for loss of tailrotor effectiveness in right turns and the phenomena may occur in varying degrees in all single main rotor helicopters at airspeeds less than 30 knots.

Verbatim NTSB analysis and probable cause from the NTSB dataset