Preflight and Start Attempt
The pilot completed a preflight inspection of the aircraft and loaded passengers on board. The aircraft had been idle for about a month. On the first start attempt, the engine turned over very slowly, prompting the pilot to discontinue the start cycle.
Hand-Propelling Incident
The pilot exited the aircraft to pull the propeller through several revolutions. As he did so, the engine suddenly started and went to a high power setting. The pilot tried to get back into the cockpit but had trouble with the door latch. He then attempted to restrain the aircraft by holding the tail but was knocked to the ground.
Collision and Damage
The aircraft ran into a hangar, bending a wing spar.
Pilot's Reflection
The pilot stated that on reflection he believes that he forgot to turn off the magnetos completely before trying to turn the propeller through the revolutions.
Probable Cause (from source)
The probable cause is the pilot's failure to completely turn off the magnetos before hand-propelling the engine.