Incident Overview
On December 12, 2018, at approximately 12:50 local time, a serious incident involving a near midair collision occurred over the Julierpass in Grisons, Switzerland. The two aircraft involved were a Cessna 172S (registration HB-CQW) operated by Albis Wings and a Piper PA-32R-301 (registration HB-PES) operated by the Segel- und Motorfluggruppe Grenchen. Both were conducting training flights under visual flight rules (VFR) and were destined for Samedan Airport (LSZS). The closest proximity between the aircraft was 250 meters horizontally and 100 feet vertically, classified as an Airprox Category A (serious risk of collision).
Flight Details
The Cessna 172S departed Hausen am Albis (LSZN) around noon with a pilot, a flight instructor, and a third person on board. The flight focused on tactical mountain flying and familiarization with Samedan. The Piper PA-32 departed Grenchen (LSZG) earlier that morning with a pilot and a flight instructor. Both aircraft were equipped with transponders but lacked collision warning devices.
Sequence of Events
After reporting off to Zurich Information near Bivio, the Cessna crew flew at the recommended minimum altitude of about 8500 ft AMSL toward the Julierpass. To practice, the Cessna executed two turning maneuvers (canyon turns) over the pass. After completing the turns, the pilot contacted Samedan AFIS for landing. At that moment, the crew spotted the Piper approximately 100 ft above and 250 m ahead, descending with landing gear extended. The Piper crew did not see the Cessna and only learned of its presence after the Samedan AFIS controller informed them following their own landing call. Both aircraft landed safely shortly after 13:00.
Visibility and Equipment
Weather conditions were excellent with clear skies and excellent visibility. However, the fresh snow on the slopes of the Julierpass created challenging contrast conditions. The Cessna is a high-wing aircraft, while the Piper is a low-wing design, which limited upward and downward visibility during the encounter. The absence of collision warning devices was identified as a contributing factor; the investigation noted that if both aircraft had been equipped with compatible collision warning devices and the pilots had responded appropriately, the dangerous approach could have been avoided.
Reporting and Findings
The incident was not immediately reported to the mandatory reporting point (REGA alarm center) as required by Swiss regulations. Instead, a report was filed later via the EU occurrence portal on December 18, 2018. The investigation also highlighted that the Cessna's practice turns over the Julierpass, a key entry and exit point for traffic to Samedan, were conducted without a blind call to inform other airspace users, indicating a lack of safety awareness.
Conclusion
The Swiss Transportation Safety Investigation Board (STSB) concluded that no further investigative results were expected beyond those already identified. The case underscores the limitations of the see-and-avoid principle, especially between high- and low-wing aircraft, and the importance of collision warning technology.