What happened
On February 1, 2022, a Piper PA-31-350 was conducting an air ambulance mission, transporting a patient and two medical personnel, from the Desierto de Atacama Aerodrome (SCAT) to Diego Aracena Aerodrome (SCDA) in Iquique, Chile. After departing from runway 35, the aircraft reached an altitude of 3,500 feet when the crew noticed a drop in manifold pressure and RPM in the number two (right) engine.
Following the initial performance loss, the right engine began showing signs of fire. The flight crew immediately declared an emergency and requested a return to the departure airfield. Upon arrival at SCAT, the aircraft landed on taxiway Bravo, where it was met by airport rescue and firefighting services. All five occupants—two pilots and three passengers—evacified the aircraft safely without injury.
The investigation
DGAC Chile investigators examined the aircraft's maintenance history and the physical condition of the engines. The investigation confirmed that the operator was following all approved maintenance programs and that the aircraft had undergone a 100-hour/annual inspection approximately six weeks prior to the event, which had revealed no issues with the dual magneto.
Technical analysis focused on the right engine's components. A specialized maintenance facility inspected the Bendix dual magneto and found it heavily damaged by fire. The inspection of the engine nacelle also revealed fire damage to the air deflector and various components located between the accessory case and the turbocharger.
Findings
- The primary cause of the incident was an internal electrical failure within the dual magneto of the number two engine.
- The fire is presumed to have originated between the ignition harness and the distributor block.
- While the specific trigger for the electrical failure could not be determined due to the extent of the fire damage, the resulting fire caused significant damage to the engine nacelle.
- The dual magneto was within its operational limits, with 759 hours of service remaining before its scheduled overhaul.
- The flight crew followed emergency procedures, including shutting down the engine and feathering the propeller, which facilitated a safe return.