Robin DR 400 / ASW 27 mid-air — see-and-avoid limits and broken CWS

In a mid-air collision at about 3,200 m AMSL, 600 m AGL, 350 m west of Piz Neir, a Robin DR 400 with four occupants and an ASW 27-18 were destroyed and five occupants killed. The Robin had departed Samedan at 17:19 for Locarno; the glider had launched at 12:15 from Amlikon, turned at the Matterhorn, and was returning. The pilots failed to acquire each other visually in time, with non-functional, switched-off or incompatible collision-avoidance equipment contributing: the Robin's CWS was inoperative or off and had no ADS-B out; the glider's FLARM was on but its transponder off, and the Robin's Mode-S was incompatible with FLARM.

1. Glider XC from Amlikon: ASW 27-18 winch-launched 12:15 at Amlikon (LSPA); routed via Walensee, Disentis, Airolo, south side of Rhone valley to the Matterhorn (turned at ~3 700 m, 15:33), then back via Valsertal and Safiental, climbed at Piz Platta and glided toward Piz Neir at 3 450 m. Pilot used supplemental oxygen.
2. Robin VFR transfer Samedan→Locarno: Robin DR 400/140 B (4 occupants) departed Neuchâtel→Samedan 15:29-16:35, then Samedan (LSZS) at 17:19 climbing for Locarno (LSZL) via Maloja, in FIC Zürich contact.
3. Robin CWS inoperative or off: The Robin's collision-warning system was not functional and probably not switched on. Mode-S transponder ON, but no ADS-B out functionality.
4. Glider transponder off: The ASW 27-18's FLARM (Flarm + Mode-S receive) was operating, but the glider's transponder was off. The Robin's Mode-A/C return to ground radar could not be processed by the glider's FLARM.
5. Convergence in Class E, see-and-avoid: Both VFR aircraft converged 350 m west of Piz Neir at ~3 200 m AMSL (~600 m AGL). The Robin's radio exchange with FIC Zürich ended at 17:28:42; the collision occurred within five seconds.
6. Collision in cruise: The aircraft collided; both became uncontrollable and entered descent. The glider pilot attempted to deploy his rescue parachute.
7. Both aircraft destroyed, 5 fatal: All occupants fatally injured; both aircraft destroyed. SUST cause: failure of the pilots to visually acquire each other in time, contributed to by non-functional/switched-off/incompatible collision-avoidance equipment.