What happened
On April 17, 2015, an incident occurred within the Warsaw Flight Information Region (FIR EPWW) involving two aircraft: an Airbus A320 cruising at FL 370 and an Airbus A321 climbing through FL 290 after departing from Warsaw Chopin Airport (LKPR).
Both aircraft were being managed via radar vectoring in the GAT sector. Initially, the crew of the Airbus A3 320 was instructed to execute a 10-degree right turn, while the Airbus A321 crew received a similar 10-degree right turn instruction and clearance to climb to FL 330. At the time of these instructions, the distance between the two aircraft was stable at approximately 7.4 NM.
Following these maneuvers, the Airbus A320 was cleared to descend to FL 190 while maintaining its current heading. During this descent, the Airbus A320 began to slightly accelerate. Approximately 10 seconds before the aircraft passed each other, the separation distance dropped to -7.1 NM, prompting the controller to issue an additional 10-degree turn command to the Airbus A320. At the moment of closest approach, the separation between the two aircraft was measured at 6.93 NM, which fell below the required minimum separation of 7 NM.
The investigation
The investigation examined the Air Traffic Management (ATM) environment and the performance of the Air Traffic Controller (ATC) on duty. It was established that the controller was on their second day of work and the incident occurred shortly before the end of their shift, approximately one hour and 20 minutes into their duty.
The investigation found that the number of active sectors was appropriate, although traffic density was at the upper limit of manageable levels. The controller held valid ACS ratings and medical certifications. The investigation also noted that the controller had recently completed a refresher course on unsafe situations during their initial training.
Findings
- The primary cause of the loss of separation was errors in Air Traffic Management (ATM) operations.
- A 10-knot difference in ground speed, caused by the Airbus A320 accelerating during its descent, contributed to the reduction in separation from 7.36 NM to 6.92 NM.
- High traffic volume in the sector on that day may have impacted the controller's ability to monitor the changing distance between the aircraft.
- The timing of the event, occurring near the end of the controller's shift, was a contributing factor.