What happened
On May 28, 2024, an Aéroservices Guépy 582 microlight took off from runway 24R at the Besançon - Thise aerodrome for a local flight. Shortly after departure, witnesses observed the aircraft deviating to the left during its initial climb, though it eventually returned to the runway axis. During this period, observers noted audible variations in engine speed.
As the pilot attempted a right-hand turn, the aircraft's engine performance continued to fluctuate. The microlight climbed at a steep nose-up attitude but remained at a very low altitude. The aircraft subsequently tipped onto its right side and plunged into a field near a row of trees, resulting in the death of the pilot and the destruction of the aircraft.
The investigation
The BEA examined the wreckage and the engine, which was a Rotax 5/82 two-stroke engine. Investigators found that the front carburettor's throttle slide had become blocked in the full-throttle position due to a small irregularity on the inner surface of the carburettor bore. This blockage likely caused the two carburettors to desynchronize when the pilot reduced power during the climb, leading to engine imbalance, vibrations, and a reduction in power.
Regarding maintenance, the investigation revealed that the pilot had performed much of the aircraft's upkeep himself. The engine had not undergone the manufacturer-recommended preservation procedures following a period of inactivity exceeding one year. Furthermore, the pilot's recent engine maintenance—including a piston and cylinder bore replacement—did not strictly follow manufacturer guidelines, such as the recommended engine break-in protocol.
Findings
- The primary cause of the accident was a reduction in engine power caused by the desynchronization of the two carburettors.
- The blockage in the front carburettor was likely caused by a localized external impact during maintenance.
- The pilot's lack of recent flying experience and failure to undergo a refresher flight after a long period of inactivity contributed to the loss of control during the engine malfunction.
- Incomplete engine ground tests, specifically the failure to run the engine at full power, prevented the detection of the carburettor malfunction before takeoff.