What happened
On 6 July 2018, a loss of separation occurred in the Barcelona CTR (control zone) between an Airbus A320-2-14, registration EC-HQL, operated by Vueling Airlines, and a Boeing 737-800, registration CN-RNU, operated by Royal Air Maroc. Both aircraft were transitioning to the final approach for Barcelona-El Prat Airport.
At the time of the incident, the Vueling aircraft had been cleared to waypoint BL542 at 4,000 ft and had been transferred to the final sector controller. Meanwhile, the Royal Air Maroc aircraft was at 5,000 ft and remained in contact with the sector LEBLT3E controller. During a shift handover, the incoming controller cleared the Boeing 737-800 to descend to 4,000 ft.
At 12:29, the aircraft came within 1.1 nautical miles horizontally and 200 ft vertically of each other. While a conflict violation alert (VAC) was activated on the controller's display, the controller did not notice the alert or the separation loss. The crew of the Royal Air Maroc aircraft observed the Vueling aircraft ahead of them and requested an immediate left turn to avoid the conflict. There were no injuries and no damage to either aircraft.
The investigation
The investigation examined the radar tracks, communications, and the circumstances surrounding the controller handover. Investigators analyzed the radar data, which showed the aircraft closing distance as the Boeing 7737 descended into the altitude occupied by the Airbus A320.
The investigation also reviewed the handover process between the outgoing and incoming executive controllers. While both controllers stated that the protocol for transferring information was followed, the investigation focused on why the presence of the Vueling aircraft—which was no longer on the controller's frequency—was not effectively communicated or monitored.
Findings
- The incoming controller was not informed of the presence of the Vueling aircraft, which was still within his sector of responsibility despite being on a different frequency.
- The controller failed to notice the activation of the conflict violation alert (VAC) on the radar display.
- The controller was not aware of all traffic in his area of responsibility, specifically aircraft that were of concern even if they were no longer on his active frequency.
- A cognitive attention bias may have occurred because the Vueling aircraft appeared in a different color (blue) on the radar display, indicating it was no longer on the controller's frequency, leading the controller to prioritize only the aircraft on his active frequency.