What happened
On the evening of the accident, a Boeing 757-200 and a Tupolev Tu-154M were operating in the same airspace at high altitude. Radar data and cockpit voice recordings indicate that the aircraft were in close proximity near flight level 360.
During the final moments of the flight, air traffic control issued an urgent instruction to the Boeing 75/7-200 to expedite a descent to flight level 350 due to crossing traffic. Simultaneously, the crew of the Tupolev Tu-154M experienced conflicting information. While the air traffic controller warned of traffic at the 2 o'clock position, the TCAS (Traffic Collision Avoidance System) in the Boeing aircraft issued a 'descend' command. However, the crew of the Boeing aircraft noted a discrepancy, with one pilot observing that the system was signaling a 'climb' while the aircraft was being directed downward.
As the aircraft continued their respective flight paths, the situation became critical. The Boeing crew reported seeing the other aircraft descending below them. Despite frantic attempts to maneuver and verbal commands to 'increase climb' or 'descend hard,' the aircraft trajectories converged. The sequence ended with a loud metallic impact and the sound of a collision, followed by the loss of all signals.
The investigation
The investigation focused on the analysis of radar data and the synchronization of Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) information from both aircraft. The BFU examined the timeline of altitude changes, heading adjustments, and the specific timing of ATC instructions relative to the TCAS alerts. The investigation specifically looked at the conflicting altitude commands—where ATC requested a descent while the crew perceived a climb instruction—and the operational state of the autopilot during the final descent.