ASG 29 / PC-24 airprox Cat A — see-and-avoid limits, glider transponder off

An ASG 29E/18m thermalling near Neuheim (Switzerland) and a Pilatus PC-24 on a production test flight from Buochs toward Emmen came into dangerous proximity at about 1,600 m AMSL in Class E; no damage resulted. The PC-24's flight-test engineer spotted the glider 1,300 m ahead, the pilot disengaged the autopilot, and dived right. Closest approach was about 320 m horizontally and 60 m vertically, classified Airprox Cat A. The glider pilot never saw the PC-24. The glider's Mode-S transponder was off and its PowerFlarm Core Pure does not process Mode-S, so the PC-24's TCAS got no warning.

1. ASG 29 thermal cross-country: Single-seat ASG 29E/18m thermalling at ~1 600 m AMSL near Neuheim (ZG), inbound to Hausen am Albis after an eastern leg. Mode-S transponder fitted but switched OFF; PowerFlarm Core Pure (does not process Mode-S).
2. PC-24 production test flight: Pilatus PC-24 (HB-VZZ) on a Pilatus production test flight from Buochs (LSZC); planned ILS approach to Emmen RW 22. Mode-S transponder + TCAS; in radio contact with Emmen ATC.
3. Class E, VFR see-and-avoid only: Both aircraft VFR in Class E airspace — no mandatory separation. Sunny, ~40 km visibility.
4. Glider transponder off: Glider's Mode-S transponder was off (legal in Class E; pilot cited battery use). With glider transponder off, ATC didn't see it on radar and the PC-24's TCAS received no return.
5. Convergence at ~1 600 m AMSL: At 15:28:02 the PC-24 was northbound at 200 kt GS, the glider in a wide left turn westbound at 65 kt GS; both at ~1 600 m AMSL. PC-24 flight-test engineer spotted the glider 1 300 m ahead at 12 o'clock.
6. PC-24 evasive maneuver: Pilot disengaged the autopilot and dived right (~60° bank, 5° nose-down within 5 s). Glider pilot never saw the PC-24.
7. Airprox Cat A, no damage: Closest approach at 15:28:11: ~320 m horizontal and ~60 m vertical (Airprox Cat A). Both flights continued and landed normally.