What happened
On May 13, 2003, at approximately 20:20 local time, an Avions Pierre Robin R-2112, registration EC-HQD, was conducting a flight training mission near La Campana, Seville. The flight, which began at Seville Airport (LEZL), was a dual-instruction flight involving an instructor and a student pilot.
After approximately 50 minutes of flight, while established at 4,500 feet near Fuentes de Andalucía and heading toward Tocina, the aircraft experienced a sudden drop in engine RPM. The pilot, following the established emergency procedures in the aircraft's flight manual, attempted to recover power. When the engine failed to regain performance, the pilot decided to perform an emergency landing in a nearby wheat field. The aircraft touched down and came to a stop after approximately 15 to 150 meters of ground roll. The two occupants evacuated the aircraft safely and sustained no injuries.
The investigation
The CIAIAC investigation focused on the engine's performance and the ignition system. While the fuel system, carburetor, and air intake were found to be in good condition with no signs of obstruction or water contamination, inspections of the spark plugs revealed significant issues. Specifically, the lower spark plug of cylinder number 2 was found to be heavily fouled with grease and was short-circuited, preventing ignition.
Further examination of the ignition system revealed that the left magneto's impulse coupling spring was fractured into two pieces. The investigation also noted that the engine had exceeded its 500-hour inspection interval for the magneto by approximately 50 hours. Additionally, the right magneto, which was responsible for the spark in the remaining functional plug of cylinder 2, was a conventional type without an advance mechanism, meaning it could not compensate for the timing issues caused by the broken spring.
Findings
- The primary cause of the power loss was the inoperability of cylinder number 2, resulting from a broken impulse coupling spring in the left magneto.
- This mechanical failure caused the ignition timing to be delayed until very close to top dead center.
- The simultaneous short-circuit of the lower spark plug in cylinder 2 prevented effective combustion from the right magneto.
- The engine's 500-hour magneto inspection interval had been exceeded by 50 hours.