Two employees began to perform a pushback procedure to the airplane in preparation for its departure. A ground employee was operating a Lektro electric pushback vehicle, and a second ground employee was acting as a wing-walker on the left side of the airplane. As the pushback procedure began, the vehicle began to move to a jack-knife position toward the airplane’s right engine, which was running, and the propeller was turning in the “feathered” position. At this time, the Captain and First Officer signaled to ground personnel to halt the pushback. The vehicle continued to turn about the nose of the airplane until the second employee ran to the vehicle and stopped the pushback movement. The original operator exited the vehicle on its left side toward the right wing and began walking backwards toward the turning propeller. Following a few steps back, the employee was struck by the propeller “at least twice,” before falling to the ground. The operator of the push-out vehicle and the wing-walker were not wearing ground-to-cockpit headsets at the time of the accident, because the headsets were not working properly. According to the company’s push-out/towing procedures, “when the headsets are inoperative or the ramp has been advised of lightning in the area, hand signals will be used for communication between ground personnel and the Captain and an additional ground agent will be required.” The operator reported that this was the first time that the injured employee had operated the pushback vehicle alone. Probable Cause: The ground personnel’s failure to maintain clearance from the propeller. Contributing factors were the ground personnel’s failure to comply with procedures/directives and the ground personnel’s failure to properly use equipment.