What happened
On August 7, 1999, at 08:55 UTC, a Chickinox II-3AA-5SB ultralight, registration OO-B88, crashed in a cultivated field near Senille, France. The aircraft was participating in the "Tour de France ULM" competition and had departed from Châtellerault for the first leg of the event.
Witnesses observed the aircraft performing a sudden rotation toward the ground at a low altitude, shortly after the end of its climb or the beginning of its cruise phase. As the aircraft descended, the pilot manually activated the emergency ballistic parachute. However, due to the extremely low altitude, the parachute did not have sufficient time to deploy and stabilize before the aircraft struck the ground. The impact resulted in one fatality and the total destruction of the aircraft.
The investigation
The investigation focused on the structural integrity of the aircraft and the environmental conditions preceding the flight. Investigators examined the wreckage, noting that the engine, located in the rear, was still delivering power at the moment of impact, as evidenced by the propeller blades and the entanglement of parachute lines around the hub.
Physical evidence from the wreckage showed that the aircraft struck the ground in a nose-down attitude with a right-wing roll. While witnesses suggested a left-hand spin, investigators found this difficult to confirm. The examination of the right wing revealed that the fabric was torn and wrapped around the aileron's trailing edge attachment.
Investigators also noted that the previous evening, all aircraft in the competition had been parked outdoors and secured with ropes. A severe thunderstorm with violent wind gusts had passed over the airfield that night, potentially subjecting the aircraft to significant aerodynamic stresses while moored.
Findings
- The primary cause of the loss of control was the in-flight failure of the wing fabric on the right wing extremity.
- It is believed that the fabric was weakened or damaged during the thunderstorm the previous night, likely due to uneven stresses caused by wind gusts and the method of securing the aircraft to the ground.
- During the flight, aerodynamic loads caused the weakened fabric to tear, leading to a loss of lift and increased drag on the right wing, which induced the uncontrolled flight.
- The pilot's attempt to deploy the emergency parachute was unsuccessful because the low altitude prevented the system from fully deploying and slowing the descent before impact.