Aerotow over-climb: glider fails to release, tug crashes

A Piper PA 18 tow plane was substantially damaged at Lager Hammelburg (Germany) and the tug pilot was seriously injured; the Ka 6 glider landed unharmed. Shortly after liftoff the glider climbed above the tug. The glider pilot pushed forward, the rope sagged then snapped taut, accelerating the glider into a second over-climb. With both hands on the stick the pilot did not release; the 400 daN weak link parted first. By then the tug's tail had been pulled up and it struck the ground at about 30-40 m AGL. The Ka 6's belly hook geometry combined with the late release was identified as central.

1. Aerotow takeoff RWY 28: A Piper PA 18-135 began an aerotow launch from RWY 28 of Sonderlandeplatz Lager Hammelburg with a single-seat Ka 6 glider on a 41 m polyester rope, in a light crosswind.
2. Ka 6 belly hook: over-climb risk: The Ka 6 was rigged with a belly (CG) hook rather than a nose hook, which accentuates the tendency for a glider to over-climb the tug if its trail position is not held precisely.
3. Glider over-climbs after liftoff: After a normal ground roll both aircraft lifted off; almost immediately the Ka 6 climbed above the tug, and the glider pilot pushed forward to drop back into position, going the rope slack.
4. Rope sag, snap, second over-climb: When the slack rope tightened the glider was accelerated sharply forward and upward with a sideways pendulum to the right, climbing above the tug again and unable to regain position.
5. Glider does not release in time: The glider pilot kept both hands on the stick pushing forward and did not release; the 400 daN weak link on the rope parted before any pilot release occurred.
6. Tug's tail lifts, tug crashes: While the rope was still taut the tug's tail was pulled up and it pitched nose-down, hitting the ground about 15 m right of RWY 28 from 30-40 m AGL; the tug pilot was seriously injured.