ASH 26E and Ventus CM collide head-on in shared thermal

Both pilots were fatally injured when an ASH 26E and a Ventus CM converged head-on in a shared thermal at ~1000 m AGL and the Ventus's left wing severed the ASH cockpit at the wing-fuselage junction; both gliders destroyed. Both were on cross-country flights using thermals in VFR with light cumulus at 2000 m. They approached on nearly opposite headings in the same thermal; neither pilot saw the other and no avoidance maneuver was observed. The Ventus's wing tore off and the fuselage fell into a power line and burned; the ASH 26E fell inverted onto a house roof. The Ventus pilot was found with an unopened parachute. No technical faults.

1. Two gliders thermalling on XC: Both ASH 26E and Ventus CM were on cross-country flights using thermals in VFR; engines retracted.
2. Shared thermal at ~1000 m AGL: At about 14:47 the two gliders met in the same thermal updraft near Bütthard at about 1000 m above ground.
3. See-and-avoid, no warning aids: Despite good weather the pilots did not detect each other visually in time; no onboard collision-warning equipment was carried.
4. Heading convergence unseen: The ASH 26E and Ventus CM approached on nearly opposite headings within the thermal; neither pilot recognised the developing convergence and no avoidance maneuver was observed.
5. Ventus wing severs ASH 26E cockpit: The Ventus CM's left wing struck and tore off the ASH 26E cockpit at the wing-fuselage junction; part of the ASH canopy frame was later found embedded in the Ventus wing skin.
6. Both gliders enter uncontrolled descents: The ASH 26E descended in a slight inverted attitude with its cockpit destroyed; the Ventus CM's left wing was torn off and its fuselage with right wing fell away.
7. ASH on roof; Ventus on power line, fire: The ASH 26E struck the roof of a house in Bütthard, ejecting the pilot; the Ventus CM fuselage fell into a power line and burned. Both pilots died, both gliders destroyed.