Mid-air collision between Karpf Baby and Grunau Baby over Weiningen during training flight

On April 12, 1961, a mid-air collision occurred between a Karpf-Flugzeugbau Karpf Baby and an Edmund Schneider Grunau Baby near Weiningen, Switzerland. Both aircraft were engaged in training flights as part of a gliding camp organized by the Segelfluggruppe Winterthur. The collision happened at approximately 750 meters altitude while both gliders were thermaling in the same area. The pilot of the Karpf Baby managed to parachute to safety, but the pilot of the Grunau Baby was fatally injured. The official investigation attributed the collision primarily to insufficient airspace monitoring by the pilot of the Grunau Baby.

1. Aerotow — thermaling: After an aerotow launch at 12:58 and release around 13:02, the HB-497 pilot began thermaling and rapidly gaining height in the established lift area north of Frauenfeld.
2. Shared thermal use: HB-497 entered and circled in the same thermal column where HB-512 was already circling above with the same left-hand turn direction, creating vertical proximity in the same air mass.
3. Limited experience & workload: As a relatively low-time student pilot performing a required thermaling task, the HB-497 pilot was likely highly focused on climbing performance and instrument indications, increasing susceptibility to neglecting lookout.
4. Inadequate lookout above: While climbing in the thermal, the HB-497 pilot began or continued circling without adequately monitoring the airspace above, failing to detect the higher HB-512 despite converging vertically.
5. Continued climb under HB-512: HB-497 continued to climb in the same left-hand circle beneath HB-512, with the vertical separation steadily decreasing as observed by a witness, and with the HB-512 pilot no longer keeping HB-497 continuously in sight.
6. Converging flight paths: As HB-497 rose and HB-512, likely slipping outward and no longer climbing, both gliders’ circular paths converged laterally and vertically until HB-497’s right wing leading edge appeared just below HB-512’s right wing, leaving no time to avoid impact.
7. Crash - fatal: HB-497’s forward fuselage struck the trailing edge of HB-512’s right wing, tearing it off; HB-512 entered an uncontrolled descent from which the pilot bailed out safely, while the severely damaged HB-497 went into a steep dive and crashed, fatally injuring its pilot.