Collision entre ASK 18B et ASW 15 près de Hasenmatt, Suisse sans blessés

Le 11 juillet 1987, un ASK 18B et un ASW 15 sont entrés en collision près du flanc ouest de Hasenmatt à Selzach, Suisse. Le pilote de l'ASK 18B a tenté d'éviter l'ASW 15 approchant en effectuant un virage serré, mais des turbulences ont causé une perte de contrôle temporaire. L'aile gauche de l'ASK 18B a frappé l'aile droite de l'ASW 15, sectionnant une partie de 2,5 mètres. L'ASW 15 a spirale vers le bas depuis environ 100 mètres, atterrissant sur un arbre puis au sol. Les deux pilotes sont restés indemnes. L'ASK 18B a subi des dommages mineurs, tandis que l'ASW 15 a été détruit.

1. Thermaling after tow: After aerotow from Grenchen, the ASK 18B was thermaling on the west side of Hasenmatt among several other gliders in rough, locally turbulent lift.
2. Crowded soaring area: Between Grenchenberg and Weissenstein, 10–15 gliders were operating in the same general area, increasing traffic complexity and the need for separation.
3. Rough turbulent thermals: The thermals were described as irregular and rough with local medium to strong turbulence, making stable circling more difficult.
4. Tightening turn for spacing: Seeing the ASW 15 approaching from the left about 50–100 m lower, the ASK 18B pilot tightened his right-hand turn to give the other glider more room toward the slope.
5. Wing lifted and stall: As bank was increased, a gust lifted the ASK 18B’s left wing, the aircraft briefly entered an uncontrollable attitude with an aerodynamic stall and nose drop, and it rapidly lost vertical separation with the ASW 15.
6. Wing-to-wing collision: Before the ASK 18B could be fully recovered to level flight, its left wing struck the ASW 15’s right wing from behind, tearing off a 2.5 m section and sending the ASW 15 into a steep spiral from about 100 m AGL.
7. Mid-air collision: The ASW 15 crashed through a fir tree to the ground and was destroyed while the pilot was uninjured, and the ASK 18B, with minor left-wing damage, remained controllable and landed safely back at Grenchen.