What happened
On June 30, 2015, a serious incident occurred within the Warsaw Flight Information Region (FIR EPWW) involving two commercial aircraft. The first aircraft, an Airbus A320 with registration DAIZB operated by Deutsche Lufthansa AG, was flying on a route from TOMTI to GOMED at flight level 350. Simultaneously, an Airbus A321 with registration OYKBE operated by Scandinavian Airlines System was traversing the same flight level on a route from XELOL to ADADO.
At approximately 10:35 UTC, the air traffic controller's radar system triggered a Short Term Collision Alert (STCA) yellow warning. The controller immediately instructed the crew of DAIZB to execute a left turn to a heading of 355 degrees and instructed the crew of OYKBE to perform a left turn to a heading of 130 degrees. Shortly thereafter, the aircraft crews reported engaging the Airborne Collision Avoidance System (ACAS). The Airbus A320 reported an ACAS Resolution Advisory (RA), while the Airbus A321 reported an ACAS descent command. A red STCA alert was displayed on the radar as the aircraft separation dropped to 2.9 NM, significantly below the required 7 NM horizontal separation minimum. Following the maneuvers, the Airbus A320 climbed to flight level 356, and the Airbus A321 descended to flight level 346, eventually clearing the conflict.
The investigation
The PKBWL investigation examined radar data, radio communications, and the operational status of the air traffic management systems. The investigation looked into the controller's performance, the status of the Medium Term Conflict Detection (MTCD) system, and the coordination between the aircraft and the controller during the alert sequence. The investigation also reviewed the training and qualification records of the flight crews and the air traffic controller involved.