What happened
On December 12, 2015, a loss of separation occurred within the Warsaw Flight Information Region (FIR) involving an Airbus A320 (registration FIN4TB) and an Embraer 190 (registration FIN877). The aircraft were operating on intersecting routes near the AGODU waypoint. The Airbus A320 was climbing to FL 390, while the Embraer 190 was cruising at FL 380.
During the vectoring process, the air traffic controller (EC) issued instructions to the Airbus A320 to turn left and increase its rate of climb to reach the assigned altitude. However, as the aircraft crossed FL 379, its rate of climb dropped significantly from 740 ft/min to as low as 63 ft/min due to the execution of the turn and performance changes at high altitude. Simultaneously, the Embraer 190 was instructed to perform turns to maintain separation. Despite these maneuvers, the two aircraft passed each other at a distance of only 4.8 NM, violating the required 7 NM separation minimum.
The investigation
The investigation, conducted by the Polish Air Navigation Services Agency (PAŻP), examined the workload, traffic density, and system functionality at the time of the incident. The investigation established that the sector was experiencing extreme traffic complexity, with 43 aircraft passing through the NFIR sector during the hour in question—a 25% increase over the declared sector capacity.
Investigators analyzed the performance of the P21 system, specifically the Medium Term Conflict Detection (MTCD) and Short Term Conflict Alert (STCA) functions. It was found that the MTCD function had been deactivated by both the executive and planning controllers due to frequent false alerts. Furthermore, the investigation reviewed the decision-making process of the Senior Controller, who had previously been advised of an impending traffic surge but was convinced by the controllers that sector splitting was unnecessary.
Findings
- The primary cause of the incident was errors in air traffic management (ATM) performance.
- A lack of assertiveness from the Senior Controller contributed to the decision to maintain single-sector operations despite high traffic volume.
- The sector was operating well beyond its capacity, with 42% of the aircraft in the sector performing altitude changes, significantly increasing complexity.
- The MTCD warning system was not active, preventing early detection of the conflict.
- The STCA warning activated too late to allow for an effective resolution, as the parameter was set to trigger only 60 seconds before the potential conflict reached the 7 NM threshold.
- The Airbus A320 experienced a drastic reduction in climb rate due to the combination of the turn and atmospheric conditions near the tropopause.
- A culture of "normalization of deviance" was identified, where controllers routinely operated in excess of sector capacities without reporting the increased risk.