What happened
On February 27, 2019, a Cessna C182 Skylane, registered HB-CDU, was conducting a cross-country flight from Sion to Birrfeld. The pilot was flying under Visual Flight Rules (VFR) and had chosen a direct route toward the Willisau (WIL) radio beacon to gain experience with new cockpit avionics.
Simultaneously, a Pitts Model 12 Monster, registered N75WU, departed from Triengen for a short-duration flight intended for aerobatic maneuvers.
As the HB-CDU approached the Willisau beacon at approximately 6,300 feet, the pilot observed a red biplane climbing vertically from below on the left side. The N75WU performed a maneuver that took it approximately 100 meters above the Cessna's altitude before banking over the right wing. To avoid a collision, the pilot of the HB-CDU immediately initiated a right-hand turn. The flight paths of the two aircraft crossed at an altitude of roughly 6,200 feet AMSL, resulting in a minimum horizontal separation of approximately 270 meters and a vertical separation of only 300 ft.
The investigation
The investigation examined the flight paths of both aircraft and the functionality of onboard equipment. Investigators noted that the pilot of the N75WU did not perceive any aircraft in close proximity during the maneuver. Furthermore, both pilots reported that no collision warnings were issued by their onboard equipment during the encounter.
Findings
- The area near the Willisau and Fribourg beacons serves as a frequent waypoint for IFR flights and basic IFR training. Because these locations are below Flight Level 100 in Class Echo airspace, pilots are not required to contact air traffic services, leading to high traffic density.
- Performing aerobatic maneuvers near these specific beacons creates a significant increased risk of collision due to the concentration of traffic.
- The Powerflarm collision avoidance systems on both aircraft failed to provide a warning during the encounter.
- The incident highlights that automated collision warning systems do not relieve pilots of their fundamental responsibility to maintain effective see and avoid lookout.