ASK 21 turnback after winch cable-break ends in tail-first impact

An ASK 21 was substantially damaged on a turnback after a simulated cable break during a winch launch at Olten; both occupants uninjured. The instructor held 437 hours on type but had not flown a winch launch for years and had no prior winch instruction; the student was on his fourth winch launch. After a normal climb on RWY 05 the instructor released, estimating 120-150 m AGL — a witness said about 50 m. The pilot pushed down, double-released and said he would land straight; the instructor called a left turn. At 45 degrees off heading airspeed decayed and takeover came too late; the tail struck first and the fuselage broke behind the wings.

1. Training winch course, 4th launch: SG Thun has no winch at home and organised a two-day winch conversion course at Flugfeld Olten (LSPO) on 27-28 September 2014, using two club two-seaters and the Olten winch infrastructure. The pilot on the front seat — about 80 hours total on gliders and three previous winch launches in Germany — was on his fourth winch launch ever, working toward his winch endorsement. The 15:38 LT flight together with the instructor was uneventful; this was the second flight, launched at 15:55:43 LT from runway 05.
2. Instructor: 11-yr winch gap: The instructor in the rear seat held a glider FI rating with 437 hours on the ASK 21 and over a hundred aerotow cable-break exercises. He had earned his winch-launch endorsement in 2003 with 16 winch launches in an ASK 21, of which two were cable-break exercises, all from the front seat. He had not flown a winch launch since 2003 — an 11-year gap — and had never instructed a winch launch. The morning of the course he completed three winch refresher flights, including a cable-break exercise from the front seat that went without problems.
3. Misjudged release at ~50 m: After a normal climb to about 120 km/h the instructor looked over the left wing to judge attitude and height and pulled the release. He estimated the release height at 120-150 m AGL. A glider pilot on the ground later estimated the actual release height at about 50 m AGL — roughly half of the instructor's estimate. The winch operator (forewarned of the exercise) saw plenty of runway remaining for a straight landing from that height.
4. Pilot pushes, releases, plans straight: The pilot pushed the nose down somewhat less aggressively than the instructor expected, double-released to confirm the rope was free, then continued straight at about 90 km/h and announced he would land straight ahead.
5. Instructor calls turnback: The instructor judged that the runway remaining ahead was not enough and told the pilot to turn left for a 180° return and an opposite-direction landing. The pilot asked 'längt das?' — will that be enough? — the instructor affirmed, and the pilot initiated a left turn.
6. Speed decays at 45° off heading: About 45° off the runway heading the instructor noticed that the airspeed was low and the controls had become sluggish ('faul'). He took control with 'my controls' and, by the loss of control feel and the height above ground, recognised the emergency. He pushed the nose steeply down and banked hard left to regain speed and turn toward the runway.
7. Late takeover, tail-first impact: The control forces returned only a few metres above the ground while the nose was still steeply down. The instructor pulled to the maximum angle of attack to avoid a nose-first impact. The tail struck the ground first; the elevator broke off and the fuselage broke behind the wings. The front fuselage and wings slid across a meadow with the broken aft section and came to rest in a hedge. Both occupants were uninjured and exited on their own after helpers pulled the wreck out of the hedge.