What happened
On Friday, October 18, 2002, at approximately 11:30 AM, a Zenith Aircraft Zodiac CH 601 ultralight, identified as 95-NN, was conducting a local flight from the Persan Beaumont airfield. Shortly after takeoff, the aircraft's Rotax 912 engine caught fire. As the fire spread into the cockpit, the pilot jettisoned the canopy in an attempt to manage the emergency. The aircraft subsequently crashed into a flat, plowed field near Neuilly-en-Thelle. The impact resulted in one fatality, as the pilot was killed in the accident, and the aircraft was destroyed.
The investigation
Investigators examined the wreckage and found that the left carburetor had completely melted, while the spark plug ceramics for the cylinders fed by this carburetor were white in color. In contrast, the right carburetor remained in good condition with normal-looking spark plugs. The investigation focused on the rubber intake manifold flange, which connects the carburetor to the intake manifold and provides sealing and vibration damping. This component was found to be destroyed on the left side, while the right-side flange remained intact.
Physical evidence at the scene indicated that the pilot's seatbelt was unfastened at the time of impact, suggesting the pilot had unbuckled themselves to facilitate a rapid evacuation from the burning cockpit. Due to the extent of the fire and impact damage, the positions of the throttle and engine electrical switch could not be determined.
Findings
Technical analysis suggests that a failure of the left carburetor intake manifold flange caused a lean air-fuel mixture and induced heavy engine vibrations. These vibrations likely compromised the integrity of the carburetor float needles, leading to significant fuel leaks through the carburetor's vent tube. Despite the presence of a fuel collection tray, fuel was projected onto the exhaust manifolds, igniting a fire in the left side of the engine compartment.