What happened
On August 19, 2015, an Aeroflot Airbus A321, registration VQ-BOI, operating flight AFL2597, departed Venice Tessera Airport. Due to heavy thunderstorms in the area, the flight crew requested to maintain the runway heading rather than following the assigned standard instrument departure (SID). This deviation caused the aircraft to enter the Treviso Control Zone (CTR) without prior coordination between the Venice and Treviso Approach control centers.
Simultually, a pair of AMX military aircraft, operating under the callsign Guizzo 05, were performing a low pass at Treviso Sant’Angelo and were climbing to 4,000 feet. Because the two air traffic control centers were experiencing delays in telephone coordination, the controllers were unaware that the paths of the commercial airliner and the military jets were converging. The aircraft eventually intersected approximately 11 nautical miles east of Treviso airport at an altitude of 4,000 feet. The conflict was only resolved when the Airbus A321's onboard collision avoidance system issued a TCAS RA (Resolution Advisory), instructing the pilot to climb.
The investigation
The ANSV investigation focused on the coordination between Venice APP (managed by ENAV SpA) and Treviso APP (managed by the Italian Air Force). The investigation examined the technical and procedural limitations of the communication links between the two centers, which relied on point-to-point telephone lines that required manual response to establish contact. The inquiry also reviewed the radar data and the sequence of instructions provided by the controllers during the critical minutes of the encounter.
Findings
- The primary cause was a critical lack of direct and immediate communication between the Venice and Treviso Approach centers, which prevented timely separation management when unpredictable traffic interference occurred.
- Coordination was hindered by the reliance on telephone-based communication that was not instantaneous.
- A lack of assertiveness in the decision-making processes of both air traffic control teams contributed to the event.
- The military AMX aircraft were not equipped with ACAS, meaning they relied entirely on ATC instructions and the commercial aircraft's TCAS to avoid the collision.
- Severe weather conditions (thunderstorms) necessitated the flight path deviation that initiated the conflict.