ASK 21 / Swiss Air Force PC-9 airprox Cat A — see-and-avoid limits, 250 kt closure

Near Fruthwilen at about 1,200 m MSL, a Swiss Air Force Pilatus PC-9/F and an ASK 21 on a VFR training flight just after aerotow release from Amlikon converged in a Cat A airprox; no one was injured. The PC-9 was at about 250 kt IAS. The student saw the PC-9 first and the instructor began evasive action at about 1 km; the PC-9 pilot saw the glider only mid-evasive and mistook the attitude for aerobatics. Closest approach was about 250 m horizontal and under 50 m vertical. FLARM did not warn as the PC-9 had no compatible CWS; the aircraft were also on different airfield frequencies. See-and-avoid reaches its limits at high closing speeds.

1. ASK 21 post-aerotow VFR training: ASK 21 (HB-1630) released from aerotow at about 1 350 m AMSL after launch from Amlikon, flying east toward Fruthwilen at about 60 kt over the ground on Amlikon radio frequency.
2. PC-9 military training overflight: Swiss Air Force PC-9/F on a VFR training sortie from Emmen flew northbound over the Amlikon area at about 1 250 m AMSL and 250 kt IAS (~275 kt ground speed), on Lommis radio frequency.
3. Class E, see-and-avoid only: Both aircraft in Class E airspace; no mandatory separation. Cloud base ~4 000 m AMSL, vis >10 km.
4. Different radio frequencies: ASK 21 on Amlikon (LSPA) frequency; PC-9 on Lommis (LSZT) frequency. PC-9 did not tune Amlikon when overflying. Neither could hear the other's position calls.
5. PC-9 had no CWS; FLARM no warning: PC-9 carried no collision-warning system. The ASK 21's FLARM did not warn — PC-9 had no FLARM/ADS-B-compatible equipment.
6. Convergence near Fruthwilen at ~1 200 m: Closing speed about 310 kt (PC-9 ~250 kt + glider ~60 kt). At ~1 km separation, the student spotted the PC-9 and the instructor initiated an evasive (bank + nose-down).
7. PC-9 pilot misread the evasive: The PC-9 pilot saw the glider only when it was already in the evasive attitude (~200 m left-front) and perceived it as an acrobatic figure, not an avoidance maneuver.
8. Airprox Cat A, no injuries: Closest approach was about 250 m horizontal and under 50 m vertical, six seconds after the evasive maneuver began; both flights continued without incident.