What happened
On June 7, 2013, an ASW20 glider, registration F-CGCQ, was preparing for a winch launch at the Mantes-Chérence aerodrome. The pilot positioned the aircraft at the start of runway 12, several dozen meters ahead of the runway threshold. At this specific location, the grass was approximately 20 centimeters high, as the area had not been recently mown.
During the takeoff roll, an assistant held the left wing level to maintain lateral stability. Once the aircraft gained momentum and the assistant released the wing, the left wing began to descend. As the wing made contact with the tall grass, the aircraft experienced a sudden asymmetric drag, causing it to pivot and flip onto its back. The winch operator immediately stopped the cable tension and engaged the emergency stop, but the aircraft remained attached to the cable. The accident resulted in one fatality and the destruction of the aircraft.
The investigation
The BEA investigation focused on the stability of the aircraft during the initial takeoff phase and the environmental conditions. Investigators noted that the aircraft was using a winch attachment point located near the center of gravity, which provides less restorative torque during lateral instability compared to a forward attachment point.
Witnesses reported that the pilot, an experienced instructor with approximately 7,000 flight hours, had noted a slight leftward correction was needed during pre-takeoff checks. The investigation also examined the takeoff area, noting that while the runway itself was maintained, the area ahead of the threshold—where the pilot had positioned the aircraft to increase the effective cable length—contained unmanaged, tall vegetation.
Findings
- The primary cause of the accident was the asymmetric drag caused by the wing contacting tall grass, which triggered a 'cartwheel' phenomenon.
- The use of the area ahead of the runway threshold to increase cable length was a known deviation from club instructions and contributed to the accident by placing the aircraft in unmaintained terrain.
- The aircraft's configuration, with the winch hook positioned near the center of gravity, made it difficult to recover from lateral instability once the wing dipped.
- At the time of the accident, there was no published procedure for handling aircraft destabilization during the takeoff roll.
- The pilot may have failed to release the cable due to the rapid onset of the rotation or an attempt to maintain control of the wing level rather than executing an immediate release.