What happened
On November 10, 2018, at approximately 19:20 local time, two aircraft were conducting approaches to Adolfo Suárez Madrid-Barajas Airport within the Madrid Control Zone. The first aircraft, an Embraer ERJ 190 (registration EC-KRJ) operated by AERONOVA, was cruising at flight level FL290. The second aircraft, an Airbus A320 (registration HA-LPM) operated by WIZZ AIR, was at flight level FL310.
During the sequence, air traffic control authorized the Airbus A320 to descend to FL300. The crew did not initially acknowledge this instruction. When the controller repeated the command, an error occurred: the controller stated a descent to FL200 instead of FL300. The crew of the Airbus A320 acknowledged the instruction by repeating the incorrect level of FL200 and subsequently began their descent.
Shortly after, the crew of the Embraer ERJ 190 alerted controllers that the other aircraft had passed in front of them at close proximity. The investigation established that the minimum separation reached was only 200 ft vertically and 0.2 NM horizontally. The crew of the Embraer ERJ 190 reported receiving a TCAS Traffic Advisory (TA) for 7 seconds, though no Resolution Advisory (RA) was issued. Following the incident, controllers instructed the Airbus A320 to maintain its level and eventually authorized the Embraer ERJ 190 to descend to FL280. Both aircraft completed their approaches and landed safely.
The investigation
The CIAIAC examined flight data from the Quick Access Recorders (QAR) of both aircraft, as the main flight data recorders had been overwritten. The investigation analyzed communications between the aircraft and air traffic control, as well as radar data which showed a Conflict Alert Violation (VAC) on the controller's screen. The investigation also reviewed reports from the flight crews and the air traffic controller involved.
Findings
- The primary cause of the loss of separation was an erroneable instruction provided to the crew of the Airbus A320 regarding their target descent level.
- A significant contributing factor was high frequency congestion, as numerous aircraft were attempting to communicate on the same frequency simultaneously, creating communication difficulties.
- The crew of the Airbus A320 performed the descent based on the incorrect level (FL200) provided during the repeated instruction.
- The crew of the Embraer ERJ 190 maintained high situational awareness and proactively alerted controllers to the proximity of the other aircraft.