What happened
On February 9, 2015, a Bombardier DHC-8-400 was operating at flight level 240 within the Warsaw Flight Information Region (EPWW). During the flight, the crew received information regarding another aircraft descending from a higher altitude. Approximately five seconds after this notification, the aircraft's Traffic Collision Avoidance System (TCAS) issued a Resolution Advisory (RA).
In response to the alert, the flight crew executed a descent maneuver of 700 feet. Following the completion of the maneuver, the flight continued its scheduled route without further incident.
The investigation
The Polish State Commission on Aircraft Accident Investigation (PKBWL) conducted an investigation into the encounter to determine the circumstances surrounding the TCAS activation.