What happened
On Wednesday, April 25, a SOCATA TB 20, registration F-GGNO, was conducting an IFR professional flight from Muret to Limoges. During the flight, air traffic control redirected the aircraft to a route further west than originally planned due to an ongoing exercise. While cruising at flight level 110, the aircraft entered a cloud layer characterized by light icing conditions and thunderstorms, with an outside air temperature of -7 °C.
During this phase of flight, the engine suddenly failed, and the fuel flow indicator rapidly dropped to zero. The pilot immediately initiated emergency procedures, including setting the mixture to full rich, activating the fuel pump, and switching to the alternate fuel tank. The aircraft began a descent at a rate of 1,000 feet per minute. Approximately one minute after the engine failure, the pilot engaged the alternate air lever, which resulted in an immediate engine restart. The aircraft had lost approximately 2,000 feet of altitude before the pilot regained control and decided to return to the departure area. No injuries were reported, and the two occupants remained safe.
The investigation
The investigation focused on the cause of the engine shutdown and the effectiveness of the pilot's response. Investigators examined the aircraft's technical condition following the event and reviewed the meteorological conditions at the time of the incident. Post-flight inspections of the SOCATA TB 20 revealed no mechanical or technical defects in the engine or fuel systems.
Findings
- The engine failure was caused by the clogging of the air filter by ice, which restricted the airflow necessary for combustion.
- The pilot did not proactively use the alternate air lever, despite the presence of icing conditions.
- The aircraft's operating manual specifies that the alternate air lever should be pulled when flying in icing conditions, specifically during precipitation or when flying in clouds with an outside air temperature of +5 °C or lower.