Incident Details
A pilot was hand-propping an airplane lacking an electric starter. A passenger who had flown with him twice since the previous fall occupied the front seat. The pilot directed the passenger to hold the heel brakes with her toes and initially verified her ability to do so by pushing on the propeller hub. He then returned to the cockpit and explained the application of full-aft elevator stick to prevent propeller airflow from raising the tail, as well as the use of the throttle, which he opened 1/8 to 1/4 inch for the start. The pilot also explained the use of the magnetos, had the passenger turn the magneto switch through the "Both" and "Off" positions twice, and advised her to switch the magnetos off if anything went wrong.
Sequence of Events
After priming the engine, the pilot called out "brakes - set" and confirmed them by attempting to push the airplane from the propeller hub. He then called out "stick - back" and confirmed elevator movement. The pilot threw the propeller, and on the third attempt, the engine caught. As the pilot walked around the wingtip to enter the airplane, the airplane began rolling. He called out for the passenger to turn off the magnetos, but the airplane rolled into a parked airplane. The pilot did not report any mechanical anomalies with the airplane, nor did he indicate the use of other securing devices such as chocks or a tail tie-down.