The glider was lined up on the northern tug strip of unpaved runway 28 at Vinon aerodrome, behind the tug plane. The pilot, who was in the front seat, and the passenger signalled to the wing runner on the left side of the glider that they were ready to take off. The runner lifted the left wing, raised his arm to the tug pilot to signal that he could take off, and then accompanied the wing for about 10 metres. After a few metres of the take-off run, the left wing dropped a first time almost to the ground and then came back up, but not to the horizontal. Thereafter, the glider remained tilted to the left.
As the glider lifted up from the ground at an indicated airspeed of about 80 km/h, the right wing suddenly rose upwards and the left wing touched the runway. The pilot pulled on the tow cable release. The glider spun around its left wing, lifted up and fell back onto the runway. The tail broke off and the glider came to rest in the opposite direction to the take-off direction.
The glider's towed take-off was conducted with a significant crosswind component and in gusty conditions. During the take-off run, the right wing rose up once and the pilot corrected this using stick and rudder inputs, but did not manage to bring the wing back to a perfectly level attitude. As the glider lifted off the ground, the right wing rose up once again, probably under the effect of a gust of wind, and the left wing tip touched the runway.
The pilot likely had difficulty controlling the glider during rotation in the face of a gusty crosswind. By the time she had pulled the release handle, it was too late to prevent the glider from cartwheeling.
The following factors may have contributed to the loss of control of the aircraft during the take-off run:
- The pilot of the tug plane and the pilot of the glider gave insufficient consideration to the possibility of the glider’s maximum demonstrated crosswind component being exceeded during the take-off run. The investigation could not determine whether the pilot applied sufficient input on the aileron control to counter the crosswind and keep the wings level.
- The take-off was performed on a runway that had tall grass in certain places, which could have destabilised the glider during the take-off run.
- The late decision to release the cable even though roll control of the glider had not been ensured during the take-off run.