What happened
On March 15, 2006, at Cuatro Vientos Airport in Madrid, a private Cessna 172 (registration EC-GOZ) was prepared for a flight to Fuentemilanos. After several failed attempts to start the engine due to a low battery, the pilot and passengers exited the aircraft to retrieve an external battery. The pilot left the throttle at approximately 1/4 position and the mixture set to rich. While the passengers were away, the pilot attempted to rotate the propeller by hand.
This action resulted in the engine starting unexpectedly. Because the throttle was advanced and the mixture was rich, the aircraft accelerated rapidly across the apron. The pilot was unable to board the aircraft in time to apply the brakes. The moving Cessna 172 struck a parked EC-IEH with its propeller and right wing. The impact caused the two aircraft to become entangled, and the momentum caused the nose of EC-IEH to strike a third parked aircraft, EC-CSX.
The movement eventually slowed enough for the pilot to re-board the aircraft and shut down the engine. No injuries were reported among the crew or passengers, but the Cessna 172 and EC-IEH sustained significant damage, while EC-CSX suffered minor damage.
The investigation
The CIAIAC investigation focused on the engine start conditions and the state of the aircraft's controls. Investigators found that the engine started normally, implying the magneto key was in a functional position rather than the OFF position. Although the parking brake was functional, it was likely either disengaged or released by the sudden movement of the engine. The investigation also noted that the engine configuration—primed multiple times with an advanced throttle and rich mixture—made a manual start highly probable during propeller rotation.
Findings
- The primary cause of the accident was the performance of a manual engine start without taking necessary precautions.
- The pilot's limited flight experience and the long interval since his last flight (eight months) likely contributed to the improper application of engine start procedures and the failure to perform basic safety checks.
- The engine was left in a highly combustible state for starting, with the throttle advanced and the mixture rich.
- The pilot's intention was only to rotate the propeller to facilitate a later start with an external battery, but the actions taken were functionally identical to a manual start.