Aerotow abort from soft grass; glider stalls past runway end

The pilot of an ASK 21 was seriously injured when the glider struck a ditch embankment past the runway end on an aerotow takeoff; substantial damage, instructor-candidate uninjured. The Varga 2180 tug accelerated poorly on the soft grass strip and the glider lifted off early into a high tow position, loading the tug hook downward so the nose wheel stayed pinned. The tug pilot aborted at ~91 km/h, ~160 m short of the end; the glider overflew the tug, banked left to clear a fence and stalled over a creek. A paved runway of equal length was available; the prior tow had also been sluggish, but its crew was not consulted and no abort plan briefed.

1. Aerotow takeoff on grass RWY 27: An ASK 21 was launched behind a Varga 2180 tug from the soft grass RWY 27 at Hausen am Albis on a training check flight; an equal-length paved runway was available alongside.
2. Soft grass strip; paved alt unused: The grass strip was softer than expected. The previous aerotow on the same runway had also accelerated sluggishly, but the crew was not consulted and no abort briefing was carried out.
3. Tug slow to accelerate: The Varga 2180 tug reached only ~40-45 mph (~65-72 km/h) on the ground roll; ~65 mph was required to lift off. All three wheels stayed on the ground throughout the run.
4. Glider lifts off early in high tow: The pilot rotated early and the ASK 21 lifted off at minimum speed, tail briefly touching the ground, then climbed to ~3-4 m above the tug, pitching it nose-down and pinning its nose wheel.
5. Tug pilot aborts at ~91 km/h: The tug pilot, concluding he could not fly safely, cut power, called an abort, released the rope, and steered left toward the paved runway. The instructor-candidate then released the glider.
6. Glider stalls past runway end: Unaware of the tug's position behind, the pilot chose to overfly a ditch and land beyond it. The glider banked left to clear a fence, then stalled over the creek, nose dropping.
7. Pilot seriously injured: The glider struck the far bank below the rim, yawed ~150 degrees and stopped ~10 m beyond. The front-seat pilot was seriously hurt; the rear-seat candidate was uninjured.