What happened
On June 22, 2015, a commercial Bombardier DHC-8-Q400 operating a flight from Rzeszów to Warsaw was descending to FL140 when the crew received a TCAS "TA" (Traffic Advisory) alert. Simultaneously, an Italian Air Force M346 was climbing through FL150 after departing from Dęblin. The climb of the M346 toward FL370 caused a loss of separation with the descending commercial aircraft.
Air Traffic Control (ATC) at the GAT ACC Sector "R" issued instructions to both aircraft to halt their vertical movements and execute turns to avoid a collision. The minimum vertical separation between the two aircraft reached approximately 40 and horizontal separation was approximately 5 NM. Following these maneuvers, both crews resumed their flight plans according to their original flight plans.
The investigation
The investigation examined the coordination sequence between various air traffic service units, including Dęblin Tower, FIS Warszawa, and ACC GAT. Investigators reviewed the communication logs and radar data, noting that the M346 crew had requested a climb at a maximum vertical rate of over 8,000 ft/min. The investigation also looked into the handoff procedures between military and civilian air traffic control authorities and the effectiveness of the P_21 system's filters, which prevent adjacent controllers from seeing certain traffic without active coordination.
Findings
- The primary cause of the incident was the issuance of an inconsistent air traffic control clearance by the ACC authority regarding the M346.
- The M346 crew requested a very high rate of climb (exceeding 8,000 ft/min), which limited the effectiveness of the ACAS/TCAS system.
- The Dęblin Tower clearance for the M346 included a cruising level of FL370 without any altitude restrictions, which allowed the aircraft to enter controlled airspace without proper coordination.
- The FIS Warszawa controller failed to stop the M346's climb despite observing it crossing FL100 and failing to ensure proper coordination before transferring the aircraft to the ACC GAT frequency.
- The FIS Warszawa controller experienced difficulty managing radar tracks and high traffic volume during the event.
- The coordination process for flight clearances involved multiple different agencies (military and civilian), and the specific procedures for this handover were not clearly described in the operational instructions of the involved units.