What happened
On March 6, 2019, at Kägislen airfield (LSPG), a Piper J3C-65/L-4 with registration HB-ONA was involved in a ground collision. Following refueling, the pilot moved the aircraft to a grass parking area. Because the aircraft lacks an electric starter, the engine must be started manually by hand-propping.
As the pilot attempted to start the engine alone, he decided not to use wheel chocks, believing the soft ground would provide sufficient resistance to prevent movement. Upon successfully starting the engine, the pilot realized the throttle had been set too high. In an attempt to pull the throttle back to idle, the pilot slipped on the grass, losing contact with the aircraft. The uncontrolled Piper J3C-65/L-4 rolled toward a hangar, striking it with the left wing. The momentum caused the aircraft to pivot around the wing, leading the propeller to strike the wooden hangar wall, which ultimately stopped the engine.
The investigation
SUST examined the procedures for starting the engine on this specific aircraft type. The investigation established that because HB-ONA does not have a parking brake, the aircraft must be secured during hand-propping using either a rope tether or chocks on both sides. Standard operating procedures suggest setting the throttle approximately 1 cm from the rear stop, roughly 1200 RPM.
Findings
- The pilot did not use wheel chocks to secure the aircraft.
- The throttle setting used during the start was significantly higher than the recommended level.
- The lack of aircraft securing was the primary cause of the uncontrolled movement that led to the collision.