What happened
On September 23, 1967, at approximately 14:00 local time, a ground collision occurred at the Bex airfield in Switzerland. The pilot of a Piper J3C, registration HB-ONH, had moved the aircraft out of a hangar to prepare for a flight with a passenger.
While the passenger was seated in the rear, the pilot attempted to start the engine by hand-propping the propeller. During this process, the engine ignited successfully, but the aircraft immediately began to taxi forward. The moving aircraft struck a parked Jodel DR-1050 M1, registration HB-EEU, which was positioned approximately 10 meters away. The pilot attempted to rush to the cockpit to stop the movement, but the metal propeller of the Piper struck the right wing of the Jodel five times, causing severe damage to the stationary aircraft's wing.
The investigation
Investigators examined the sequence of the engine start-up and the instructions provided to the passenger. The investigation established that the pilot had instructed the passenger to depress the pedals to apply the brakes. However, the pilot failed to account for the fact that the aircraft featured two sets of pedals: one for the rudder and one for the brakes. The passenger likely manipulated the rudder pedals instead of the brakes. Furthermore, the investigation noted that the aircraft was not secured with chocks, and the pilot had not followed standard ground instruction safety protocols regarding passenger supervision during hand-propping.