Incident Overview
On May 8, 2020, at approximately 15:28 local time, a serious airprox incident occurred in Class Echo airspace near Neuheim, Canton Zug. The event involved a Pilatus Aircraft PC-24 registered as HB-VZZ and an ASG 29E/18 m glider registered as D-KAVE. The investigation was conducted by the Swiss Transportation Safety Investigation Board (STSB) under Article 45 of the relevant safety investigation regulations.
Operational Context
The PC-24, operated by Pilatus Flugzeugwerke AG, was conducting a production flight test from Buochs (LSZC). The crew consisted of a Pilot-in-Command and a Flight Test Engineer. They were flying under Visual Flight Rules (VFR) and had established radio contact with Emmen air traffic control. In contrast, the glider, owned by SGKA Segelfluggruppe Knonaueramt, was on a private cross-country flight from Hausen a/A (LSZN). The glider pilot was climbing in thermic lift to an altitude of approximately 1600 m/M.
Sequence of Events
At 15:28:02, the Flight Test Engineer in the PC-24 visually identified the glider directly ahead at the same altitude, roughly 1300 meters away. The engineer immediately notified the pilot via intercom. The pilot disengaged the autopilot and initiated a controlled evasive maneuver to the right and downward. Within five seconds, the aircraft achieved a bank angle of approximately 60 degrees and a nose-down attitude of 5 degrees.
The minimum separation between the two aircraft occurred at 15:28:11, with a horizontal distance of about 320 meters (0.17 NM) and a vertical difference of roughly 60 meters (195 ft). Both crews subsequently continued their flights and landed safely without further incident.
Findings and Analysis
Weather conditions were clear with visibility around 40 km, ruling out meteorological factors as a cause. The glider pilot did not visually detect the PC-24 at any point. The glider's PowerFlarm device issued no warnings, and its transponder was off, which was not mandatory in this context. The PC-24's TCAS also provided no traffic advisories or resolution alerts regarding the glider.
The investigation noted that while the "see and avoid" principle applies in Class Echo airspace, human visual limitations can hinder detection, particularly of slender aircraft like gliders during turns. The prompt identification by the PC-24 crew and their decisive evasive action were critical in preventing a collision.