What happened
On April 1, 2015, an air traffic management incident occurred within the Warsaw Flight Information Region (FIR EPWW) involving two aircraft: an Airbus A319 and an Airbus A320. Both aircraft were operating at flight level 380. The A319 was traveling on the BOKSU - TUSIN route, while the A320 was following the YABER - TUSIN route.
To maintain the required 7 NM horizontal separation due to converging flight paths, the air traffic controller reduced the speed of the Airbus A319 to M077 and cleared the Airbus A320 to fly direct to the MIKOV waypoint at a speed of M079. During the maneuver near the EVINA waypoint, the crew of the Airbus A319 began to accelerate. The controller subsequently issued heading instructions to the Airbus A319, directing it to turn left to a heading of 200°, and later left again to 180°. As a result of these maneuvers, the Airbus A319 passed behind the Airbus A320 at a distance of approximately 6.8 NM, failing to maintain the required 7 NM separation.
The investigation
The investigation examined the actions of the air traffic controller and the coordination between sectors. It was established that the controller was on their second shift following two days of rest and held all necessary valid licenses and medical certifications. The investigation found that while initial measurements of the aircraft's ground speeds did not immediately suggest a separation breach, the controller failed to coordinate a flight path change for the Airbus A319 with ACC Prague, which could have increased lateral separation. Furthermore, the controller did not verify the specific wind conditions at flight level 380 before issuing vectoring instructions. Strong, variable winds were present in the sector at the time of the incident, which slowed the Airdo A320 and accelerated the Airbus A319.
Findings
- The primary cause of the incident was errors in air traffic management (ATM) operations.
- A lack of coordination with ACC Prague regarding the Airbus A319 flight path prevented the increase of lateral separation.
- The controller failed to account for the impact of local wind conditions on the aircraft's ground speeds when issuing vectoring commands.
- The controller did not provide necessary traffic information to the crews.
- While an alternative of descending the Airbus A320 to FL370 was possible, the controller had previously approved the aircraft's entry into FL380 and chose to manage the conflict through speed regulation instead.