Défaillance structurelle fatale lors du lancement par treuil du SZD 24-4A Foka 4 à l'aérodrome de Bicester

Le 8 août 2010, un SZD 24-4A Foka 4 a subi une défaillance structurelle catastrophique lors d'un lancement par treuil à l'aérodrome de Bicester, dans l'Oxfordshire. Les ailes se sont détachées du fuselage peu après le décollage, entraînant un accident mortel pour le pilote, qui était le seul occupant. L'enquête a révélé que le boulon conique inférieur de l'attache principale de l'aile n'était pas complètement engagé lors du montage, ce qui a conduit à la défaillance. Le planeur a été détruit lors de l'incident, et deux recommandations de sécurité ont été émises à la suite des conclusions.

1. Preflight assembly: On the morning of the accident, the pilot and friends rigged G-DBZZ for flight at Bicester Airfield, carefully consulting the Flight Manual as none of them had rigged this type before.
2. Wing joint misrigged: During rigging, the lower bevel bolt of the wing main fitting did not fully engage with the lower lug stack of the main spar joint, leaving the primary wing attachment only partially secured and undetectably misrigged.
3. Engagement not verifiable: The design of the wing main fitting allowed the pilots to complete the specified number of turns and feel little resistance, yet provided no means to verify full engagement of the lower bevel bolt.
4. Pilot reassurance: After a first, uneventful but low winch launch during which the canopy opened, the pilot discussed the rigging and canopy issue with the owner by telephone and was reassured that the rigging had been done correctly.
5. Winch launch - climb: On the second winch launch, the glider accelerated and rotated into a climb that some witnesses perceived as slightly fast and steep, remaining on the cable as it climbed through several hundred feet.
6. Wing attachment failure: While still on the winch, the left wing bent upward about 20 degrees followed by the right wing, the lower bevel bolt failed, and both wings folded upwards and separated from the fuselage while remaining attached to each other at the main spar joint.
7. Crash - fatal: With the wings detached, the fuselage pitched steeply nose-down and struck the ground, destroying the glider and fatally injuring the pilot.