What happened
On June 13, 2015, a loss of separation occurred near the ABERO waypoint within the Warsaw Flight Information Region (EPWW). Two aircraft, identified as Airbus A302A and Airbus A320B, were operating on opposing tracks at flight level 360. The first aircraft was traveling from DIBED toward BOKSU, while the second was traveling from BOKSU toward DIBED.
At approximately 05:29:40, the air traffic controller (ATC) identified a conflict between the two aircraft, which were roughly 24 nautical miles apart. To prevent a collision, the controller issued heading changes: the crew of Airbus A320A was instructed to turn left by 15 degrees, followed shortly by an additional 10-degree left turn. The crew of Airbus A320B was instructed to turn left by 10 degrees. Despite these interventions, the Short Term Conflict Alert (STCA) transitioned from yellow to red, and the aircraft eventually passed each other at a distance of 5 nautical miles, failing to maintain the required 7 nautical mile separation.
The investigation
The investigation examined radar data, radio communications, and the sequence of controller interventions. The inquiry focused on the workload within the sector and the impact of other traffic on the controller's ability to manage the conflict. The investigation also reviewed the timeline of communications from a third aircraft performing photogrammetric flight operations in the same sector.
Findings
- Traffic density in the sector was high but remained within acceptable limits.
- A photogrammetric flight operating in the sector significantly increased the workload for both the air traffic controller and the procedural controller. The pilot of this aircraft provided very long transmissions, including one lasting approximately 40 seconds immediately prior to the conflict detection.
- The combination of high traffic volume and the intensive communication requirements of the photogrammetric flight likely contributed to the late detection of the conflict between the two A320 aircraft.
- While the controller's corrective actions were appropriate, the investigation noted that larger heading changes (of 30 to 40 degrees) or an instruction to change flight levels could have successfully maintained the required separation.
Safety action
- The ATM event investigation team prepared a report for the reporting controller containing the findings of the investigation.