What happened
On June 27, 1999, at 17:20, a Stampe SV4C aircraft, registration F-BFUB, was performing aerobatic maneuvers near the Nancy Essey airfield. The pilot had departed from the aerodrome and proceeded to a designated aerobatic area. The flight sequence began with two loops, followed by a diving recovery and an inverted flight maneuver.
During the vertical descent phase of the maneuver, the engine ceased operation. The pilot attempted to restart the engine while the passenger, who was the aircraft owner, took control of the aircraft to prepare for an emergency landing. Due to the low altitude, the crew determined there was insufficient height to attempt a restart via a dive. The aircraft subsequently touched down at the edge of a plowed field and entered a cultivated field, where the aircraft rolled onto its back.
There were two persons on board; the pilot and the passenger both survived the impact, though the aircraft sustained light damage.
The investigation
The investigation focused on the engine's performance during inverted flight and the fuel delivery system. The aircraft was equipped with a Renault 4-P03 engine and a 60 IGSA carburetor designed to facilitate inverted flight. This specific carburetor utilizes a weighted valve that shifts position based on gravity to regulate fuel flow when the aircraft is upside down.
Investigators examined the engine and the carburetor mechanism to determine if a mechanical failure preceded the accident. The technical documentation for the carburetor noted that while the system is designed to maintain correct fuel flow at full throttle during inverted flight, it is not intended for sustained inverted flight or slow rolls, as the mixture tends to enrich at lower power settings. Post-accident examination of the engine revealed no malfunctions occurring prior to the impact.