Aircraft Accident/Incident Report

Albany, Kentucky 42602
Friday, November 8, 2002 13:45 EST

The pilot flew the helicopter at a steep approach angle to clear obstacles. At 30 to 35 feet above the ground, in a slow forward hover, the helicopter crossed over the approach end of the landing zone. It then started an uncommanded turn to the right that the pilot could not arrest with left pedal input. The pilot attempted to go around, but the helicopter kept rotating to the right, and the pilot's ability to reduce power was limited due to obstacles. The pilot also attempted to "weather vane" the helicopter; however, it would not align with the wind, and the rate of rotation increased. With the helicopter continuing to spin to the right, the pilot maneuvered it over the landing zone, closed the throttle, arrested the spin, and completed an autorotation. A tail strike occurred during the landing flare. According to the pilot's diagram of the accident scene, winds were about 50 degrees left of helicopter centerline during the approach. Winds reported at area airports were approximately 90-100 degrees left of helicopter centerline during the approach, at 11 to 15 knots, gusting to 18 knots. Unanticipated yaw can occur in the direction of main rotor torque reaction. Contributors to unanticipated yaw include: relative wind blowing towards the tail rotor thrust outflow, the main rotor tip vortex being directed into the tail rotor, and additional torque demand produced by power increases when airspeed drops below translational lift. The most effective way to avoid unanticipated yaw is to avoid the relative wind contributors.

The pilot's inadequate in-flight planning, which resulted in an angle of approach in relative wind conditions conducive to a loss of helicopter tail rotor effectiveness. A factor was the obstacles surrounding the landing field.