What happened
On June 14, 2022, a De Havilland DHC8-400, registration SP-EQI, was operating within the Ostrava APP airspace (Czech Republic), climbing toward FL 110. After being transferred to Kraków APP, the crew received clearance to climb to FL 250. Simultaneously, an Airbus A321, registration D-AIDG, was descending through FL 309 toward FL 190 on a path toward the PADKA waypoint.
At 18:01:38 UTC, the Airbus A321 contacted Kraków APP and was instructed to descend to FL 130 and proceed via the STAR PADKA 3G approach. While the initial separation between the two aircraft appeared sufficient, the reduction in distance between them triggered a Short Term Collision Alert (STCA) from the PEGASUS_21 system at 18:04:19 UTC. At the time of the alert, the aircraft were 8.14 NM apart on converging tracks, with a predicted minimum distance of 3.18 NM.
Upon noticing the alert, the Executive Controller (EC) issued urgent instructions: the Airbus A3 and21 was ordered to turn right to a heading of 120° and level off, while the De Havilland DHC8-400 was ordered to level off immediately. Although these maneuvers increased the horizontal distance to 3.9 NM, the vertical separation dropped to 300 ft, which was below the required 1,000 ft minimum. The separation was eventually restored to legal limits by 18:05:36 UTC. The crews did not report any TCAS activations.
The investigation
The investigation examined the actions of the Kraków APP controller and the operational environment during the incident. The investigation focused on the coordination tasks being performed by the Executive Controller and the Planning Controller at the time of the separation loss. The investigation also reviewed the system alerts generated by the PEGASUS_21 surveillance system.
Findings
- The primary cause of the loss of separation was the temporary loss of situational awareness by the Executive Controller.
- The controller's attention was heavily diverted by the need to coordinate transit conditions for another aircraft and manage radio communications with other traffic in a different sector of the Kraków TMA.
- The complexity of the traffic situation, characterized by a high volume of required coordination tasks, contributed to the incident.
- The separation loss occurred while the controller was managing multiple simultaneous coordination efforts within the TMA.