What happened
On August 15, 2003, at 20:08 UTC, an air traffic incident occurred in the airspace over Bern involving two commercial aircraft. The first aircraft, a Boeing 737 (registration TC-APR) operated by Pegasus Airlines, was climbing through flight level 288 toward flight level 300. Simultaneously, a Condor Airbus A320 (registration D-AICB) was descending through flight level 308, also targeting flight level 300.
As the two aircraft approached each other on nearly parallel tracks, a Short Term Conflict Alert (STCA) was triggered. The air traffic controller instructed the Pegasus crew to halt their climb at flight level 295 to maintain vertical separation. During this maneuver, the aircraft came within 400 ft of vertical separation and 1.4 NM of lateral separation. Both crews reported receiving TCAS (Traffic Alert and Collision Avoidance System) advisories, including resolution advisories, which prompted the aircraft to perform evasive maneuvers.
The investigation
The investigation focused on the air traffic control environment at the time of the incident. The event took and occurred during a period when the Zurich Upper 1 (U1) sector was being closed and merged with the Upper 2 (U2) sector due to low traffic volume.
Investigators examined the handover process between controllers. During the consolidation, the Radar Executive (RE) position was being transitioned. The controller who had originally cleared the TC-APR to climb to flight level 300 was no longer the active controller managing the frequency when the conflict was identified. The investigation also reviewed the technical performance of the radar monitoring systems and the communication between the aircraft and the controllers.