Mid-air collision between Ka 2 B and S 18 near Siblingen, Switzerland
On May 16, 1965, a mid-air collision occurred between an Alexander Schleicher Ka 2 B and a Spalinger S 18 II A near Siblingen, Switzerland. Both gliders were engaged in thermaling operations when they collided due to insufficient airspace monitoring. Despite significant damage to the S 18's right wing, the pilot managed to land safely near Schaffhausen airfield. The Ka 2 B also landed safely with no injuries reported. The incident was attributed to inadequate airspace observation by the S 18 pilot.
- Aerotow — thermaling: After an aerotow launch at 16:56, the S-18 HB-315 released near the Siblinger Schlossranden and began thermaling in weak, broken lift over the west side of the ridge.
- Weak broken lift: The S-18 was operating in marginal, irregular lift with alternating strong climb and sink, requiring frequent corrections and making height-keeping and separation more difficult.
- Instrument-focused flying: Concerned with the irregular up- and downdrafts, the S-18 pilot spent considerable time looking at the instruments and outside toward the ridge and horizon rather than systematically scanning for traffic above.
- Inadequate lookout above: Although he had previously seen the Ka-2b about 50 m higher, the S-18 pilot continued circling without considering that the other glider might also be thermaling above in the same core and did not check the airspace above.
- Converging thermaling paths: Both gliders flew roughly a full circle in the same area with only 20–50 m vertical separation, and the fluctuating lift reduced their height separation until the S-18’s right wingtip struck the Ka-2b’s fuselage around 17:05.
- Damaged glider flown back: After feeling the impact, the S-18 pilot rolled out of the turn, confirmed the aircraft was still controllable despite significant damage to the right wing, and headed toward Schaffhausen airfield.
- Outlanding - damage: Due to increased sink from the wing damage, the S-18 could not quite reach the runway and made a safe outlanding in a field about 50 m short of the Schaffhausen strip, with substantial wing damage but no injuries.