Foka 4 wings fold on winch launch — bevel bolt not fully engaged in rigging

The pilot of an SZD-24-4A Foka 4 was fatally injured when both wings folded up and separated from the fuselage during a winch launch at Bicester; destroyed. The pilot — who had not rigged this type before — assembled the glider per the Flight Manual; the lower bevel bolt of the wing main fitting did not fully engage with the lower lug stack and the design provided no way to verify engagement. A first low winch launch was uneventful; on the second, the left wing bent up ~20°, the right followed, the bolt failed and both wings folded up and separated while still joined at the spar; the fuselage pitched nose-down to the ground.

1. Rigging by pilot, new to type: On the morning of the accident the pilot rigged the SZD-24-4A Foka 4 with friends at Bicester; none had rigged this type before, and they consulted the Flight Manual throughout.
2. Lower bevel bolt not fully engaged: During rigging the lower bevel bolt of the wing main fitting did not fully engage the main spar joint's lower lug stack, leaving the primary wing attachment only partially secured.
3. No way to verify bolt engagement: The wing main fitting's design let the crew complete the specified turns while feeling little resistance, with no means by feel or procedure to verify full engagement of the lower bolt.
4. First winch launch — low, uneventful: An initial winch launch was carried out and remained uneventful at low height; the canopy opened during the launch but the glider landed safely.
5. Owner reassures by phone on rigging: After the first launch the pilot discussed the rigging and the canopy issue with the owner by telephone; the owner reassured him that the rigging had been done correctly.
6. Second winch launch — climb: On the second winch launch the Foka 4 accelerated and rotated into a climb that some witnesses perceived as slightly fast and steep, climbing through several hundred feet on the cable.
7. Wings bend, bolt fails, wings separate: While still on the winch the left wing bent upward ~20°, then the right; the lower bevel bolt failed and both wings folded up and separated from the fuselage, staying joined together.
8. Fuselage nose-down impact; pilot fatal: With the wings detached the fuselage pitched steeply nose-down and struck the ground. The pilot was fatally injured and the airframe destroyed.