Colisión entre ASK 18B y ASW 15 cerca de Hasenmatt, Suiza sin heridos

El 11 de julio de 1987, un ASK 18B y un ASW 15 colisionaron cerca del flanco oeste de Hasenmatt en Selzach, Suiza. El piloto del ASK 18B intentó evitar el ASW 15 que se aproximaba realizando un giro cerrado, pero la turbulencia causó una pérdida temporal de control. El ala izquierda del ASK 18B golpeó el ala derecha del ASW 15, cortando una sección de 2,5 metros. El ASW 15 descendió en espiral desde aproximadamente 100 metros, aterrizando en un árbol y luego en el suelo. Ambos pilotos resultaron ilesos. El ASK 18B sufrió daños menores, mientras que el ASW 15 fue destruido.

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.