What happened
On March 1, 2021, an Agusta Westland AW109SP helicopter, registration HB-ZRR, was conducting a primary rescue mission from Samnaun to Chur, Switzerland. While cruising at approximately 9,500 ft AMSL over Austrian airspace, the crew suddenly observed a shadow followed by a white light aircraft approaching from the south. The unidentified aircraft crossed the flight path of the helicopter with a vertical separation of only about 30 to 50 meters. The near-collision occurred northeast of Gross Litzner in Class E airspace.
The investigation
Investigators examined radar data from both Swiss and Austrian civilian and military sources, but found no radar tracks of an aircraft crossing the helicopter's path at the time of the incident. The crew confirmed they were monitoring relevant mountain and airport frequencies, but no other traffic was reported. Onboard collision avoidance systems, including the Traffic Advisory System (TAS) and the Floice system, failed to provide any prior warning. The investigation also reviewed the operational environment, noting that while the weather was clear, the visual identification of the second aircraft was significantly hindered by the white color of the plane and the snow-covered mountain background.
Findings
- The unidentified aircraft likely had no functioning transponder or was operating without one, which prevented the HB-ZRR's TAS from detecting the threat.
- The lack of a warning from the Floice system suggests the second aircraft was not equipped with Flarm technology.
- Visual identification was extremely difficult due to the high crossing angle and the visual camouflage created by the white aircraft against the snowy landscape.
- The crew was unable to perform an evasive maneuver because the aircraft was detected too late.