What happened
On December 17, 2003, an airprox incident occurred within the Zurich Terminal Control Area (TMA) involving a De Havilland Canada DHC Dash 8 (registration ISK210) and a private DV20 Katana (HB-SCO). The Dash 8 was operating a scheduled commercial flight from Berne to Vienna with 30 passengers and three crew members. Simultaneously, the pilot of the DV20 Katana was conducting a private visual flight from Grenchen toward Samedan.
At approximately 11:56 UTC, the two aircraft crossed paths with minimal separation. Radar records indicate the lateral distance between the aircraft was only about 150 to 200 meters, with an altitude difference of roughly 200 feet. The pilot of the DV20 Katana reported noticing the Dash 8 only after the aircraft had already crossed his flight path.
The investigation
The investigation by the SUST established that the DV20 Katana entered the Zurich TMA without the required authorization or radio contact with air traffic control. While the Dash 8 was flying under instrument flight rules (IFR) and in constant communication with Zurich Sector South/West, the private pilot was flying under visual flight rules (VFR) and was not in contact with any control unit at the time of the encounter.
The investigation examined the radar settings and controller responsibilities. At the time, the air traffic controller (ATCO) at the South/West sector was conducting a check with a trainee. While the Short Term Conflict Alert (STCA) system triggered at 11:55:28, alerting controllers to the conflict, the ATCOs noted that the VFR aircraft was not previously known to them.
Findings
Several contributing factors led to this high-risk encounter:
- Unauthorized Airspace Entry: The pilot of HB-SCO entered the Zurich TMA without permission. The pilot intended to fly below the TMA but climbed higher than planned to avoid an active military firing area.
- Loss of Situational Awareness: The pilot of the DV20 Katana was heavily focused on monitoring weather conditions and approaching mountains, which led to a failure to monitor instruments and observe the surrounding airspace effectively. The aircraft's low-wing design may have also obscured the view of the Dash 8.
- Climb Rate Discrepancy: Although the crew of ISK210 was instructed to climb at a maximum rate of 1500 ft/min, they climbed at an average rate of only 650 ft/min, which placed them in the path of the unauthorized aircraft.
- Radar Limitations: The airspace allocated to Berne included a technical suppression area for STCA alerts, and the specific radar monitors were set to a range that did not immediately highlight the unauthorized VFR traffic.