What happened
On the night of July 11, 2014, two Airbus A3/20 aircraft, both operated by Vueling, experienced a significant loss of separation during their approach to Barcelona Airport (LEBL). The first aircraft, EC-IZD (flight VLG6107), was arriving from Amsterdam, while the second, EC-LZZ (flight VLG8305), was arriving from Rome.
The incident began when air traffic control (ATC) issued an instruction to EC-IZD to intercept the localizer for the ILS approach to runway 02. However, the crew of EC-IZD did not hear the instruction. Instead, the crew of a preceding aircraft, EZY68EF, mistakenly read back the instruction intended for EC-IZD. Because the instruction was acknowledged, the controller believed the message had been received by the correct aircraft.
As a result, EC-IZD maintained its previous heading, crossing the localizer and placing itself on a convergent course with EC-LZZ. Although the controller identified the deviation and instructed both aircraft to turn right to avoid a conflict, the separation continued to decrease. During the execution of these evasive maneuvers, the two aircraft reached a minimum separation of only 1.1 NM horizontally and 200 ft vertically.
The investigation
The CIAIAC investigation focused on three distinct phases of the event. First, the investigators examined the period two minutes prior to the encounter, identifying critical errors in the communication chain. It was established that the instruction to EC-IZD was not heard by its crew and was erroneously read back by the preceding aircraft. The controller did not detect that the readback was from the wrong aircraft, partly due to high workload and the fact that the readback was provided immediately.
Second, the investigation analyzed the controller's detection of the danger. While the controller correctly identified the deviation and issued avoidance instructions, the investigation found that the instructions did not convey the necessary urgency or the specific reason for the maneuvers (the presence of conflicting traffic). This lack of urgency, combined with the activation of TCAS Resolution Advisories (RA), contributed to a delay in the crews' execution of the turns.
Finally, the investigation reviewed the period of closest approach. The findings showed that the loss of separation actually occurred while the aircraft were performing the evasive maneuvers instructed by ATC, as the crews were reacting to the TCAS alerts.
Findings
- The primary cause of the incident was the failure of the EC-IZD crew to execute an ATC instruction because they did not hear it.
- The error was compounded because the instruction was incorrectly read back by a different aircraft, which went undetected by both the flight crews and ATC.
- The controller's instructions for avoidance did not communicate the urgency or the reason for the maneuver, which may have delayed the crews' response.
- The aircraft were operating in a high-density airspace environment with heavy communication frequency usage.