Incident
On 24 November 2018 at 16:10 local time, a serious incident occurred near Sursee, Canton of Lucerne, Switzerland. Two aircraft, a Reims Cessna F172P (registration HB-CIO) and a Gyroflug SC 01 Speed Canard (registration HB-UCT), converged with a minimum horizontal separation of 0.1 nautical miles and zero vertical separation. The event was classified as an Airprox with ICAO category A.
Aircraft and Pilots
Aircraft 1: HB-CIO, a Reims Cessna F172P owned and operated by Flugschule Eichenberger AG, Buttwil. It was equipped with a Mode-S transponder and a PowerFlarm collision warning device. The pilot, a Swiss national born in 1952, held a PPL(A) and had 272.5 total flight hours, with 215.5 hours on type.
Aircraft 2: HB-UCT, a Gyroflug SC 01 Speed Canard privately owned and operated. It was equipped with a Mode-S transponder but no collision warning system. The pilot, a Swiss national born in 1964, held a PPL(A) and had 3126 total flight hours, with 2926 hours on type.
Sequence of Events
HB-CIO departed Buttwil for Langenthal and returned. After leaving Langenthal frequency, the pilot set Buttwil frequency and flew at about 4500 ft on a heading of 090° south of the Willisau VOR. Over Sursee at approximately 4000 ft AMSL, the pilot saw an aircraft to his right moving toward him and turning sharply left. He estimated the lateral distance at 50 m and vertical at 30 ft above. He identified the aircraft as a canard design.
HB-UCT was returning from a sightseeing flight from Birrfeld. At just below 4000 ft AMSL over Sursee in a slight climb, the pilot spotted an aircraft about 300 m away, slightly higher and to the left. He identified it as a Cessna from Flugschule Eichenberger. He immediately initiated an evasive left turn and crossed behind the Cessna.
Neither pilot received an aural or visual warning from collision avoidance systems. The HB-UCT pilot had Zürich Information on 124.700 MHz for listening awareness. Both aircraft continued and landed at their destinations.
Equipment
Both aircraft had Mode-S transponders. HB-CIO had a PowerFlarm device, which was coupled to the avionics master switch and displayed traffic on a Butterfly Avionics display. The pilot of HB-CIO was unaware that the aircraft was equipped with this device. HB-UCT had no collision warning system. Radar data showed that the aircraft converged at a constant angle of about 120°, creating a "constant bearing, decreasing range" scenario that hindered visual detection.
Evasive action by the HB-UCT pilot prevented a probable collision. The HB-CIO pilot detected the other aircraft only during the evasive maneuver.
Analysis and Conclusions
The analysis noted that both pilots were able to see each other only at the last moment, necessitating evasive action. For HB-CIO, the other aircraft was outside the pilot's field of view to the right and may have been obscured by the cabin structure or the passenger. For HB-UCT, the Cessna was about 60° left of flight path and likely masked by the canard's elevator ahead of the cockpit.
The PowerFlarm on HB-CIO could theoretically have received the HB-UCT transponder signal, displaying distance and relative height without directional information. However, the pilot did not notice any warning.
The report concluded that while collision warning systems are recommended for this category of aircraft, they are not mandatory. When only one aircraft has such a system, warning capabilities are limited. In this case, visual detection and avoidance (see and avoid) were the primary means of collision avoidance.