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: At 15:11 LT on 13 April 2013 a Piper PA 18-135 began an aerotow launch from RWY 28 of Sonderlandeplatz Lager Hammelburg (EDFJ) with a single-seat Ka 6 glider on a 41 m polyester rope. Wind was about 240° at 10 kt (≈6 kt crosswind from the left); weather was not a factor. The glider was the tug pilot's fourth aerotow of the day.
2. Ka 6 belly hook: over-climb risk: The Ka 6 was rigged with a belly (CG) hook rather than a nose hook. BFU noted that a belly hook accentuates the tendency for the glider to over-climb the tug if its trail position is not held precisely, both during the initial climb and along the tow.
3. Glider over-climbs after liftoff: After a normal ground roll both aircraft lifted off. Almost immediately the Ka 6 climbed above the tug. The glider pilot pushed forward on the stick to drop back into the trail position; the rope went 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. It climbed above the tug a second time, displaced laterally and unable to regain the trail position.
5. Glider does not release in time: The glider pilot kept both hands on the stick to push forward and did not actuate the release. Per SBO 2.2.10 the procedural response when over-climb cannot be controlled is to release the tow rope without delay. 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 under tension the tug's tail was pulled up; the tug pitched nose-down. The tug pilot lost sight of the glider in the rear-view mirror and reported releasing his end of the rope before impact. The Piper struck the ground about 15 m right of RWY 28 at 30–40 m AGL; the cockpit, wings and engine mounts were torn apart. The tug pilot was seriously injured. The Ka 6 pilot flew two 180° turns at low altitude and landed back on the airfield unharmed.