Overview
On December 12, 2015, at 18:43 UTC, an Airbus A320 (call sign FIN4TB) and an Embraer 190 (call sign FIN877) passed each other at a lateral distance of 4.8 nautical miles, below the required minimum separation of 7 NM. The incident occurred near the AGODU waypoint within the Warsaw Flight Information Region (FIR EPWW). The A320 was en route from EDDT (Berlin Tegel) to EFHK (Helsinki Vantaa) climbing to flight level (FL) 390, while the E190 was en route from EFHK to LFPG (Paris Charles de Gaulle) at FL 380. Both aircraft were under air traffic control by the Executive Controller (EC) of sector NFIR.
Sequence of Events
The Executive Controller detected the conflict when the aircraft were 23.5 NM apart, with the A320 crossing FL 375 in climb. The controller instructed FIN4TB to turn left 15 degrees and accelerate climb to reach FL 390. The pilot acknowledged, but during the turn, the climb rate decreased from 740 ft/min to 63 ft/min (as recorded by Mode S) due to the maneuver. FIN877 was instructed to turn left 20 degrees, then an additional 10 degrees, and was provided traffic information. The pilot of FIN4TB reported visual contact with the other aircraft. The minimum distance measured was 4.8 NM. After separation was restored, the controller cleared both aircraft for own navigation: FIN877 to BODLA and FIN4TB to KUNER. FIN4TB continued climbing to FL 390 with an average rate of about 500 ft/min.
Workload and Traffic Conditions
At the time of the incident, between 18:00 and 19:00 UTC, 43 aircraft transited sector NFIR, exceeding its declared base capacity of 40 aircraft per hour. Occupancy data indicated temporary overloads around 18:30–18:40. The controller team had received sufficient rest prior to the shift. The Planning Controller (PC) was coordinating with ACC Bremen during the critical moment and could not detect the erroneous clearance issued by the EC. The Medium Term Conflict Detection (MTCD) system activated an alert at 18:35:03, but it was not visible on the main display because both controllers had disabled it. The Short Term Conflict Alert (STCA) prediction activated at 18:43:08, and a violation alert at 18:43:33.
Climb Performance of FIN4TB
Analysis of climb data from the P21 system showed that the A320’s average climb rate from FL 100 to FL 360 was 1573 ft/min. After passing FL 370, performance significantly degraded, with average climb rates below 556 ft/min before reaching FL 380. At FL 379, following the controller’s instruction to expedite climb, the climb rate dropped to 63 ft/min (IV parameter) or 94 ft/min (BV parameter) due to the turn.
Conclusion
The source does not provide a stated probable cause.