What happened
On February 8, 2020, a near-collision occurred near the Clariden-Hüfifirn mountain landing site in Switzerland. The incident involved two light aircraft operating under Visual Flight Rules (VFR) in Class E airspace.
The first aircraft, a Robin DR 400 (registration HB-KLZ), was conducting a sightseeing flight around the Matterhorn. While returning to Mollis, the crew flew over the Hüfipass at a high ground speed of approximately 150 knots. Simultaneously, a Piper PA-12 (registration HB-PPJ), used for flight training, was performing reconnaissance maneuvers for a landing at the same mountain site. The Piper was executing a left turn into a crosswind pattern at a much lower speed of 78 knots.
At 10:43 AM, the two aircraft passed within 12 meters horizontally and 21 meters vertically of each other. Following the encounter, both crews continued their flights as planned, landing safely at their respective destinations.
The investigation
The investigation examined the flight paths, equipment, and environmental conditions. Both aircraft were equipped with advanced safety technology, including Mode S transponders, compatible FLARM collision warning systems, and strobe lights. Both crews were monitoring the same mountain frequency and were aware of other traffic in the area.
Investigators analyzed the visibility and weather, noting that conditions were clear with excellent visibility, meaning the weather did not contribute to the event. The investigation also looked at the flight profiles, noting that the crew of the HB-PPJ was following standard procedures for mountain landing reconnaissance.
Findings
Several factors contributed to the close encounter:
- The primary cause was that neither crew visually identified the other aircraft before the encounter.
- The high speed of the HB-KLZ (150 knots) significantly reduced the time available for detection and avoidance.
- The high-wing configuration of the HB-PPJ obstructed the pilots' view of the HB-KLZ during the initial phase of the left turn.
- The choice of flight path and speed by the HB-KLZ crew when overflying an active mountain landing site was considered risky.
- The presence of multiple other aircraft in the immediate vicinity likely made it difficult for both crews to correctly associate collision warning alerts with the specific approaching aircraft.