Incident Overview
On 28 September 2024, in the Warsaw Flight Information Region (FIR), within the ACC sector TC Low, a loss of lateral separation occurred between two aircraft: a Boeing 737-800 (registration OM-HEX) and an Airbus 321 (registration OY-TCE). The Boeing was cruising at flight level FL350, navigating toward waypoint REVMA. The Airbus was at FL360, navigating toward OLBUV with the intention of landing at EPPO airport. Prior to the aircraft passing each other, the EC sector controller cleared the Airbus to descend from FL360 to FL310. This decision reduced the horizontal distance between the aircraft to 4.5 nautical miles, with a vertical separation of 700 feet, lasting approximately 5 seconds.
Investigation and Findings
The investigation was conducted by the Polish State Commission for Aircraft Accident Investigation (PKBWL). The direct cause of the incident was identified as the issuance by the EC sector controller of a conflicting descent clearance for the Airbus. The controller’s instruction resulted in inadequate separation between the two aircraft.
Contributing Factors
A contributing factor might have been an erroneous change of personnel at the controller working positions, which could have affected situational awareness. However, the investigation did not definitively confirm this link.
Outcome
No safety recommendations were proposed or implemented by the investigating body, and no preventive measures were suggested. The commission accepted the investigation report and closed the case without issuing any further directives.