The pilot planned on starting his airplane by turning the propeller by hand, because the airplane’s battery was dead. After loading his passenger, he set the throttle and the parking brake, but he elected not to tie down the airplane or place chocks in front of its wheels. When he pulled the propeller through, the engine started immediately as he intended. However, he had placed the throttle in a position that resulted in a higher rpm than he expected. Due to the high rpm, the parking brake was unable to hold the airplane in position, and it started rolling forward with only the passenger inside. The pilot attempted to reenter the airplane, but he was unable to do so. Although the passenger was able to steer the airplane along the taxiway, she did not know how to stop it, and it eventually went through a fence and over an embankment. During the accident sequence, the fuselage and the wings were substantially damaged. According to the pilot, there were no malfunctions or anomalies with the parking brake system or the throttle mechanism.