Bell 407 crash near near Kromvlei, south of Alberton, Gauteng, South Africa

An instructor and a pilot under proficiency check were flying training exercises in the Kromvlei general flying area. After uneventful simulated engine and tail rotor failures, they began a simulated autorotation. At about 100 ft above ground level the engine did not respond as the instructor attempted the recovery, the low rotor rpm warning activated, and the helicopter descended uncontrolled and struck the ground hard on its skids. The skids spread sideways and a main rotor blade severed the tail boom. Neither occupant was injured. The Civil Aviation Authority attributed the hard landing to a delayed throttle response caused by lag in the collective control lever, with an auxiliary throttle that was not regularly inspected, had corroded through exposure to the elements, and whose deteriorating condition had not been reported.