Late side-slip exit stalls ASK 21 at 8-10 m AGL on instructor-corrected approach

Both occupants of an ASK 21 on a training flight were seriously injured when the glider stalled at 8-10 m AGL during the exit of an instructor-initiated side-slip; aircraft heavily damaged. After an unsuccessful thermal search the student steered for landing; judging the approach too high, the instructor took control and initiated a side-slip at 40-50 m AGL. He ended the slip too low; the nose pitched up well above normal as it rolled out and airspeed dropped; nose-down elevator could not recover energy in time. The glider fell from ~5 m in level attitude onto the main gear, bounced ~100 m, and re-impacted with the nose gear first.

1. Camp ASK 21 training; thermal search: Dutch club's summer camp at Rudolstadt; 12:54 winch launch of an ASK 21 with instructor + student; an unsuccessful thermal search followed, then the student steered for landing.
2. Instructor judges approach too high: Instructor judged the student's approach would land long; he took control to correct it.
3. Side-slip initiated at 40-50 m AGL: Instructor initiated a side-slip at ~40-50 m AGL to lose excess height; intended energy management for landing.
4. Slip exit at 8-10 m AGL; stall develops: The side-slip ended at only ~8-10 m AGL; the nose pitched above normal and airspeed dropped sharply as the glider stalled. Pushing forward could not recover energy at that height.
5. Falls from 5 m; bounces 100 m: Glider fell from ~5 m in level attitude, struck the ground on the main gear, bounced, and re-impacted ~100 m further on the nose gear first with a slight nose-down pitch.
6. Both seriously hurt; substantial damage: Both occupants seriously injured; glider substantially damaged. Weather not a factor. Root cause: instructor brought the glider into a stall too low to recover during the side-slip exit.