What happened
On the morning of Friday, April 26, 2002, a Humbert Tétras B ultralight, identified as 63-MI, was conducting a private flight from Chambéry toward Clermont-Ferrand. While cruising near Saint-Blaise-du-Buis, approximately eight nautical miles east of the Grenoble Saint-Geoirs aerodrome, the aircraft entered a spin. Ground witnesses observed the aircraft in a spin before it impacted a field in a steep dive. The impact was followed by a fire that destroyed the aircraft. The accident resulted in two fatalities, involving the pilot and one passenger.
The investigation
Investigators examined the flight paths of the ultralight and a nearby DC 8-72 heavy jet, which was performing circuit training at the Grenoble Saint-Geost aerodrome at the time. Ground witnesses reported seeing both aircraft in the same area shortly before the accident, with the DC 8 passing ahead of the ultralight. Radar track analysis established that the minimum distance between the estimated position of the DC 8 and the point where the ultralight lost control was approximately 0.9 nautical miles.
While the ultralight was equipped with a radio, investigators could not determine which frequency was selected, and no radio contact was established between the pilot and the Grenoble Saint-Geoirs air traffic services. Meteorological conditions at the site were reported as CAVOK with a 10-knot wind.
Findings
- The primary cause of the loss of control was the ultralight aircraft entering the wake turbulence generated by the DC 8-72.
- Driven by the wind, the turbulent wake reached the ultralight less than two minutes after the heavy jet had passed through the area.