What happened
The pilot reported that the aircraft's alternator had failed, resulting in a complete loss of electrical power. To initiate a banner towing operation, he decided to hand-prop the engine to start it. He applied the parking brake and began pulling the propeller by hand. During this process, the cockpit was left unattended. The engine successfully started, causing the aircraft to begin rolling forward despite the parking brake being engaged. The pilot was unable to regain control of the moving aircraft before it collided with a nearby hangar.
The investigation
The investigation focused on the circumstances surrounding the engine start and the subsequent loss of control. It was confirmed that the alternator inoperative condition necessitated the hand-prop start method. The sequence of events indicated that the pilot's decision to leave the cockpit unattended during the high-torque phase of a hand-prop start contributed directly to the incident.
Findings
The primary factor in this accident was the loss of control due to the aircraft moving while the pilot was not at the controls. The failure of the electrical system required an alternative starting method, but the procedure used created a hazardous situation. The collision with the hangar resulted from the pilot's inability to stop or steer the aircraft once it began to move.
Safety message
Pilots should ensure that the cockpit is never left unattended during engine start procedures, particularly when hand-propping. If an electrical failure occurs, alternative starting methods must be executed with strict adherence to safety protocols to prevent unintended aircraft movement.