What happened
On February 15, 1998, at approximately 18:00, an amateur-built pendular ultralight (identified as 63-AH) was performing a local flight from an occasional airstrip in Le Cendre, France. Following a previous solo flight, the pilot attempted a second takeoff carrying one passenger. During the takeoff roll, the aircraft experienced a significant drop in engine RPM.
To avoid a wooded valley located at the end of the runway, the pilot executed a 90-degree left turn. During this maneuver, the aircraft struck a telephone cable running parallel to the runway before crashing into an adjacent meadow. The impact resulted in two injuries (the pilot and the passenger) and caused heavy damage to the aircraft.
The investigation
The investigation focused on the mechanical failure of the Hirth 276, 40 hp, two-stroke engine. The aircraft had been out of service for approximately two years prior to the accident. Investigators examined the fuel system and the condition of the carburetor to determine why the engine power decreased so abruptly during the takeoff phase.
Findings
Technical analysis revealed that the engine had suffered a seizure. This failure was caused by insufficient maintenance, specifically an inadequate cleaning of the carburetor. Residual lubricant deposits had hardened within the system, narrowing the jet nozzle. As a result, the fuel-air mixture became too lean at full throttle, leading to the engine's loss of power and subsequent seizure.