What happened
On August 28, 2011, a PIPER PA-18-150, registration EC-JEC, departed from Sabadell airport to perform a commercial banner towing operation along the Costa Brava. During the flight, approximately 20 minutes after takeoff, the pilot experienced loud detonations from the engine accompanied by a significant loss of power.
After notifying air traffic control, the pilot determined that returning to the aerodrome was not possible and prepared for an emergency landing in a nearby field. The pilot initially selected a clear area and released the banner. During the approach to a field in the municipality of Mollet del $Valles$, the pilot identified obstacles at a low altitude, forcing a sudden right turn to a different landing site. The aircraft touched down on a plowed field with north-south furrows. The impact caused the aircraft to capsize and come to rest in an inverted position, with the vertical stabilizer embedded in the ground. The pilot escaped without injuries.
The investigation
The CIAIAC examined the engine, the ignition system, and the maintenance records of the aircraft. The investigation focused on the condition of the magnetos and spark plugs to determine the source of the engine detonations and power loss. The investigators also analyzed the pilot's decision-making process and the terrain conditions at the landing site.
Findings
- The investigation identified a failure in the left magneto, which was providing insufficient electrical current to three of the four spark plugs it serviced. This was caused by a resistance value in the secondary winding coil that significantly exceeded the manufacturer's specified range.
- Two spark plugs supplied by the right magneto were also in poor condition, showing excessive carbon buildup and electrode wear.
- The right magneto showed signs of irregular operation, including worn points and a distributor cover that had been subjected to electrical arcing.
- The investigation concluded that these ignition system defects were likely not detected during previous scheduled maintenance inspections.
- The presence of undetected obstacles during the final approach forced the pilot to deviate from a preferred landing site to a less suitable field.
- The uneven, plowed surface of the chosen field contributed to the loss of control on the ground and the subsequent capsize of the aircraft.
Safety action
- It is recommended that the maintenance provider review its periodic inspection methods for engine components, with particular emphasis on the ignition system, to ensure that defective elements are properly identified.