Unlocked airbrakes deploy on winch launch, ASK 23 B porpoises

A student pilot lost control of an ASK 23 B during a winch launch at Amlikon; the glider was substantially damaged and the student uninjured. Distracted when the instructor signalled the cable was ready to hook, the student skipped the checklist item to check and lock the airbrakes. As the winch began pulling, the unlocked airbrakes self-deployed. The glider lifted to about 1 m AGL, dropped back, and porpoised four times against the grass runway, each bounce more pronounced, up to 3 m AGL. The student released the cable and the ASK 23 B came to rest on the left edge of RWY 27 with the fuselage broken ahead of the fin.

1. Solo winch launch RWY 27 in ASK 23 B: At 11:50 LT on 6 October 2012 a student pilot began a solo winch launch from RWY 27 of Flugfeld Amlikon (LSPA) in an ASK 23 B. The launch was his first flight in a single-seat glider; total experience was about 11 hours, all on the two-seat ASK 21 at Amlikon. Six days earlier he had flown his first four solo winch launches on the ASK 21. Wind was light and westerly; weather was not a factor.
2. Checklist skip: airbrakes not locked: While the student was working through the pre-launch checklist, the instructor signalled at the 'Instruments' item that the winch cable was ready to hook. The student opened the release to hook the cable, then resumed the checklist at 'Runway' — inadvertently skipping the 'Brakes: checked and locked' item. The airbrakes therefore remained unlocked.
3. Airbrakes self-deploy on winch start: Once the winch began pulling, aerodynamic load on the unlocked airbrakes caused them to extend on their own. The drag and lift reduction during the initial climb were unexpected; neither the student nor the instructor on the wingtip noticed the deployed airbrakes during the launch.
4. Four porpoise bounces, up to 3 m AGL: Just after liftoff the ASK 23 B reached about 1 m AGL, then dropped and touched the grass runway. The cycle repeated four times, each oscillation more pronounced; the last bounce reached about 3 m AGL before the glider struck the runway nose-down at a roughly 30° pitch attitude on the nose wheel. Only at that final impact did the instructor recognise that the airbrakes were deployed.
5. Student releases cable: Sensing that the launch was abnormal after the first ground contact, the student released the winch cable. The winch driver, watching the cable parachute, reduced power and stopped the winch motor once he saw that the cable had been released.
6. Fuselage broken; no injury: The ASK 23 B came to rest about 270 m from the launch point on the left edge of RWY 27. The fuselage was broken just ahead of the fin and the left wing root, elevator, rudder and canopy frame were damaged. The student was uninjured. Post-accident examination found no pre-existing technical defects; the airbrakes and ailerons were correctly rigged and functional.