What happened
On September 13, 1968, at approximately 15:00 CEST, an incident occurred at the La Côte aerodrome in Prangins involving an Aeronca 7 AC, registration HB-ETF. Following a navigation flight, a student pilot parked the aircraft at the apron and went to the office to complete administrative tasks.
Believing the aircraft required refueling, the student pilot returned to the aircraft to taxi it approximately 100 meters to a fuel pump. Finding no assistance available, the pilot attempted to start the engine manually by hand-propping. After setting the throttle to full power and engaging the ignition, the pilot attempted to swing the propeller. On the third attempt, the engine ignited; however, the engine briefly ran at a higher power setting than anticipated. This sudden surge caused the unmually unmanned aircraft to move forward unexpectedly. In an attempt to restrain the aircraft by the right wing strut, the pilot inadvertently caused the aircraft to veer to the right, leading to a collision with a parked Piper J3C, registration HB-ONH. The impact of the propeller strikes caused extensive damage to the left wing and struts of the stationary Piper.
The investigation
The investigation established that while the student pilot had engaged the parking brake via the cockpit control, the brakes provided no actual stopping power to the wheels. It was noted that the wheels could be moved easily by hand. The investigation further revealed that the parking brake mechanism had a history of failing to engage properly, and the component was removed following the accident, preventing a technical inspection of the mechanism itself.
Findings
- The primary cause of the accident was the failure to implement effective measures to prevent the aircraft from rolling during the hand-propping process.
- The student pilot did not verify that the wheels were secured or utilize chocks, wheel blocks, or other physical restraints to stabilize the aircraft.
- The engine's sudden surge in power, likely due to the throttle being set to a high position, provided the momentum necessary for the unsecured aircraft to move.
- The parking brake mechanism was non-functional, leaving the aircraft entirely unrestrained.