Incident Overview
On June 13, 2015, an air proximity incident occurred in the Warsaw Flight Information Region (EPWW) involving two Airbus A320 aircraft, designated A320A and A320B. Both aircraft were operating at flight level (FL) 360 on reciprocal routes: A320A was flying from DIBED to BOKSU, and A320B from BOKSU to DIBED. The controller of the GAT ACC sector initiated vectoring to avoid a collision, instructing A320A to turn left 15 degrees and then an additional 10 degrees left, and A320B to turn left 10 degrees. However, these actions did not ensure the required minimum separation of 7 NM, and the aircraft passed each other at a distance of 5 NM.
Timeline
Based on radio communications and radar recordings, the sequence of events was as follows:
- At 05:11:46, the crew of A320A reported over DIBED at FL360 and was instructed to proceed direct to BOKSU.
- At 05:22:53, the crew of a photogrammetric flight aircraft first informed the controller of its intentions.
- At 05:23:42, the crew of A320B reported at FL360, flying towards DIBED.
- At 05:25:20 and 05:27:09, the photogrammetric flight crew made further transmissions, requesting clearance for own navigation.
- At 05:28:50, the photogrammetric crew requested coordination for entry into Slovak airspace.
- At 05:29:40, the controller detected the conflict between A320A and A320B, approximately 24 NM apart on opposite collision courses. The vectoring instructions were issued.
- At 05:30:21, the Short Term Conflict Alert (STCA) activated in yellow.
- At 05:31:01, A320A received an additional left turn instruction.
- At 05:31:28, the STCA activated in red.
- At 05:31:43, the conflict situation ended.
Contributing Factors
The report notes that traffic density was very high but at an acceptable level. That day, a photogrammetric flight was operating in the sector, and the pilot's lengthy transmissions, the last one lasting about 40 seconds just before the conflict was detected, significantly occupied the controller's attention. This, combined with the high traffic volume, was likely the reason for the late detection of the conflict between two aircraft at the same level on opposite routes. The controller's actions after detecting the conflict were considered correct, though the report remarks that turns of at least 30-40 degrees or a level change would have been more likely to maintain separation.
Probable Cause
The probable cause of the event was errors in air traffic management (ATM) work.