What happened
On August 10, 2000, at approximately 14:38 UTC, a Crossair Saab SB20, registration HB-IYB, was operating under IFR procedures from Guernsey to Zurich. While flying at flight level 60 within the Zurich TMA 4, approximately 6 NM northeast of EKRIT, the flight crew suddenly identified an unidentified glider at the same altitude. The glider was positioned at the 11 o'clock position and was turning toward the aircraft. The crew estimated the lateral separation to be only 0.3 NM. To prevent a mid-air collision, the pilot of the Saab SB20 immediately executed an evasive maneuver.
The investigation
The investigation established that both aircraft were operating within Class C controlled airspace. The Crossair flight was in continuous radio contact with the Zurich Arrival West Sector (APW) controller and was being tracked via radar. However, the unidentified glider was not transmitting a transponder signal and had established no radio contact with any air traffic control unit. Furthermore, the controller's radar monitor showed no primary radar echo for the glider at the time of the incident.
Findings
- The primary cause of the airprox was the unidentified glider's unauthorized transit through the Zurich TMA 4 without contacting air traffic control.
- Because the glider pilot failed to communicate with the relevant ATC unit, controllers were unable to issue instructions or clearances to maintain separation between the glider and the IFR flight CRX842.
- The risk of collision was significantly high, though mitigated by excellent visibility and the fact that the Crossair aircraft was flying away from the sun, which allowed the crew to spot the glider in time.