What happened
On October 22, 2019, an FK9 Mark 3 ultralight, registration 59CBF, was performing circuit patterns at the Chavenay Villepreux airfield. The flight, conducted for instructional purposes by Aéroclub Jean Bertin, involved an instructor and a student pilot.
During the second circuit, the aircraft approached the final segment above the theoretical glide path. The aircraft entered a sideslip maneuver, which subsequently led to a stall. The aircraft struck the ground approximately 400 meters before the runway threshold, resulting in two fatalities and the destruction of the aircraft.
The investigation
The BEA examined the wreckage and the flight path using secondary radar data from Saclay. The investigation established that during the first circuit, the aircraft maintained a stable descent. However, during the second circuit, the descent rate increased significantly to 15% during the final approach.
Technical analysis of the FK9 Mark 3 revealed that the aircraft was configured with flaps in position 2 (20°). The investigation also noted that the aircraft was not equipped with a stall warning device or a ballistic parachute. Radar data showed the ground speed dropped from 105 km/h to 65 km/h during the initial third of the final approach, with the aircraft losing radar detection at an altitude of approximately 376 feet.
Findings
The investigation concluded that the accident was caused by an asymmetric stall resulting from the combination of a high angle of attack, low airspeed, and the use of a sideslip maneuver. The aircraft was flying at a speed near its stall limit while in a non-symmetrical flight configuration.
Contributing factors included:
- The instructor's failure to detect the reduced safety margins created by the combination of the sideslip, low speed, and high angle of attack.
- The absence of a stall warning system on the aircraft.