Class C airprox: ASW 20 enters without clearance, A340 evades at 260 m horizontal

A Swiss A340 descending into Zurich and an ASW 20 passed at about 260 m horizontal separation and nearly the same altitude in TMA LSZH 2; both aircraft landed safely. The glider, on a VFR training flight from Bohlhof, had entered Class C airspace without clearance and was not visible to ATC. FLARM and TCAS II are incompatible, so no electronic warning was generated. The A340 was descending through about 1,430 m MSL on a Zurich Final clearance below the MRVA. An observer-seat pilot spotted the glider on the localizer turn; the A340 rolled 36 degrees left at 1.6 g and the glider pilot turned right. ICAO Cat A airprox.

1. A340 descent Zurich, ASW 20 at TMA edge: At 13:32 UTC on 11 August 2012 a Swiss A340-313 (flight SWR 39) was on IFR descent into Zurich from San Francisco; it was at 6000 ft QNH at 245 KIAS with a 2500 ft/min descent rate in TMA LSZH 2 Class C airspace, 17 NM north-west of the airport (over German territory). At the same time an ASW 20 (HB-1519) launched from Segelfluggelände Bohlhof was at the southern edge of TMA LSZH 2 at about 4700 ft QNH on a VFR training flight.
2. Glider in Class C without clearance: The ASW 20 had entered Class C airspace without ATC clearance and was not carrying a transponder. As a result the air traffic controller could see neither primary nor secondary returns from the glider, the A340's TCAS II could not generate a resolution advisory, and the ground-based Short Term Conflict Alert (STCA) did not trigger. The glider's FLARM and the airliner's TCAS II are not compatible. SUST identified lack of risk awareness on the glider pilot's part as a direct cause.
3. A340 cleared below MRVA: At 13:32:04 UTC Zurich Final cleared the A340 to descend to 4000 ft QNH, an altitude below the published minimum radar vector altitude (MRVA) in TMA LSZH 2. The controller did not subsequently monitor that the MRVA floor was respected. SUST found that issuing 'anticipated clearances' below the MRVA was undocumented common practice at Skyguide; an audit of 1,714 RWY 14 approaches found MRVA was undershot by more than 100 ft in 0.7 % of cases, by up to 660 ft.
4. Observer spots glider on LOC turn: While the A340 was turning onto the localizer for RWY 14, a third pilot on the centre observer seat suddenly saw the glider on a collision course at the same altitude and warned the two flying pilots.
5. A340 36° left at 1.6 g; glider right: At 13:32:35 UTC the A340 crew initiated a marked evasive manoeuvre — maximum 36° left bank, ~5° pitch up — producing 1.6 g normal acceleration. At that moment it was still in Class C at 4700 ft QNH, descending at 350 ft/min at 248 KIAS. Three seconds earlier, at 13:32:32 UTC, the glider pilot had also seen the airliner and made a brusque right turn as his own avoidance manoeuvre.
6. ~260 m horizontal pass; both land safe: At 13:32:45 UTC the two aircraft passed at approximately the same altitude with about 260 m horizontal separation. The A340 (SWR 39) continued the approach and landed on RWY 14 at 13:38 UTC. The ASW 20 continued its training flight and landed at Bohlhof at 13:59 UTC. SUST classified the encounter as ICAO Category A (high collision risk).