What happened
On August 12, 2000, at 15:12 UTC, a Swissair Airbus A320, registration HB-IJL, was operating under IFR procedures while entering the EKRIT holding pattern. While climbing to flight level 600, the first officer spotted a glider performing a left-hand turn. The aircraft were in close proximity, with the crew estimating a vertical separation of approximately 300 feet and a lateral distance of 0.4 NM. The glider was moving toward the northwest, away from the airliner.
The investigation
The investigation focused on the presence of the unidentified aircraft within the Class C controlled airspace of the Zurich TMA 4. Investigators confirmed that the Airbus A320 was in continuous radio contact with Zurich Arrival West Sector. However, the glider was not transmitting a transponder signal and had established no radio contact with air traffic services. At the time of the encounter, the air traffic controller observed no primary radar echo for the glider, though a primary blip briefly appeared later in the sequence.
To identify the glider, investigators reviewed all glider flight activities at the Fricktal-Schupfart, Birrfeld, and Schaffhausen airfields. Interviews were conducted with six pilots from these locations, all of whom denied involvement in the incident based on their recorded flight paths and altitudes. The investigation did not extend to foreign airfields near the border due to the scope of the inquiry.
Findings
- Both aircraft were operating within Class C controlled airspace.
- The Airbus A320 was operating under IFR and maintained constant communication with ATC.
- The unidentified glider was not communicating with air traffic control and was not transmitting a transponder signal.
- The lack of a primary radar return initially prevented controllers from detecting the glider's presence.
- The incident presented a high risk of collision, though the alertness of the Swissair crew and the diverging flight paths mitigated the immediate danger.