Incident Narrative
On 6 March 2019 at 16:30 local time, a Piper J3C-65/L-4 aircraft registered as HB-ONA was involved in a ground incident at Kägiswil airfield (LSPG). The pilot, a Swiss national born in 1953 holding an Airline Transport Pilot Licence (ATPL(A)), had just refueled the aircraft and pushed it to a grass parking area. The aircraft lacked an electric starter, requiring the engine to be started by hand. With no other person present, the pilot decided to start the engine alone. He did not use wheel chocks, assessing that the soft ground would provide sufficient rolling resistance. When the engine started, the pilot realized that the throttle was set too high. As he attempted to pull the throttle back to idle, he slipped on the grass and could not reach the aircraft. The aircraft began rolling toward a hangar, where its left wing contacted the hangar wall. The aircraft then rotated around the left wing, causing the propeller to hit the wooden hangar wall, which stopped the engine.
Findings
The investigation revealed that HB-ONA had no parking brake, so the aircraft had to be secured during engine start according to operational procedures. The required methods were either rope securing or the use of wheel chocks on both sides. Additionally, the throttle lever should have been set approximately 1 cm from the idle stop (corresponding to about 1200 rpm) for the starting procedure. This power setting was not visually marked and was based solely on experience.
Probable Cause
The serious incident was attributable to the fact that the aircraft was not secured against rolling away. The pilot had not used wheel chocks or any other securing method, and the power setting was higher than recommended, causing the aircraft to move forward even on soft ground.