Blanik stalls in a low turn-back after unlocked airbrakes force an early tow release

The front-seat passenger of a Blanik L-13 was seriously injured and the instructor unhurt when the glider stalled in a low turn near Cortebert; aircraft destroyed. On an intro flight the airbrakes, not locked before the aerotow, opened just after lift-off. The glider could not climb; urgent radio calls from the tug and ground went unheard on a busy frequency. Near obstacles the tug released it. Instead of landing ahead in fields to the left, the pilot turned right at low height; speed decayed and the glider stalled into a field. The cause was a stall in the low turn-back; a front-seat load ~8 kg below the minimum worsened the speed loss.

1. Aerotow takeoff: During an aerotow departure from Courtelary, the Blanik began its initial climb behind the Robin towplane.
2. Airbrakes not locked: Because the pre-takeoff check of the airbrake locking was incomplete, the glider launched with the airbrakes not properly locked, leading to their inadvertent deployment shortly after liftoff.
3. Low front seat weight: The load on the front seat, including passenger and parachute, was about 8 kg below the prescribed minimum, adversely affecting handling at low speed.
4. Radio warnings missed: Multiple urgent radio calls from the tow pilot and ground personnel about the extended airbrakes were not recognized by the glider pilot due to a congested frequency and his focus on the poor climb.
5. Towplane releases glider: Approaching Cortebert with obstacles ahead and unable to climb adequately with the glider’s airbrakes extended, the tow pilot performed an emergency release of the glider.
6. Low-altitude turn stall: After release, the glider pilot initiated a right 180-degree turn at low height, during which airspeed decayed rapidly and the glider stalled instead of landing straight ahead in available fields.
7. Crash - serious injury: The stalled glider descended into a field near Cortebert, seriously injuring the front-seat passenger, leaving the pilot uninjured, and destroying the aircraft.