Piper Archer collides with unseen ASW 15 in busy uncontrolled circuit

On 2001-06-22 around 17:50 LT, a Piper PA-28-181 and an ASW 15 collided ~400 m south of Yverdon (LSGY), an uncontrolled airfield with intense mixed traffic (powered, gliding, parachuting). The Piper, returning from Blécherette with four onboard, turned left between the runway and the powered downwind onto a path leading directly to a glider in the runway-23 loss-of-altitude area. The Piper pilot did not see the glider and struck its tail from behind at ~250 m AGL. The glider fell inverted; the Piper spun into nearby trees. Both destroyed; three fatally injured, one seriously.

1. Return to Yverdon — approach: After an aerotow departure from Yverdon at 14:49 LT and a soaring flight of ~3 hours, the ASW 15 glider HB-1013 returned to Yverdon and entered the loss-of-altitude area for RWY 23 to integrate into the landing circuit.
2. Intense local traffic: At the time of the approaches there was intense mixed traffic at Yverdon, including powered aircraft, gliders, and parachuting activity, increasing pilot workload and potential for distraction.
3. Mixed circuit operations: The glider HB-1013 and aerobatic aircraft HB-SAN coordinated their landing sequence on the common frequency while the Piper HB-PKL also approached and maneuvered in the same circuit area.
4. Piper turns toward glider: While HB-1013 was in the glider loss-of-altitude area for RWY 23, the Piper HB-PKL, having reported 'vertical terrain' and then turned left to fly between the runway and the powered-aircraft downwind, tracked a path that led directly toward the glider.
5. No effective avoidance: There is no indication from witnesses or radio calls that either the glider pilot or the Piper pilot saw the conflict in time to take effective avoiding action before impact.
6. Mid-air collision: HB-PKL collided with HB-1013 from behind, striking first the glider's tailplane and then its fuselage, fatally disrupting the glider's flight.
7. Crash - fatal: The glider fell inverted into a field and the Piper entered a spin and crashed into trees nearby, destroying both aircraft and killing the glider pilot and two Piper passengers, with one Piper passenger seriously injured.