Air Traffic Incident Involving Airbus A320 and A321 in Warsaw FIR

Incident Overview and Aircraft Details On April 17, 2015, an incident occurred in the Warsaw Flight Information Region (FIR EPWW) involving two aircraft: an Airbus A320 and an Airbus A321. The event was classified as an incident by the State Commission for Investigation of Aviation Accidents (PAŃSTWOWA KOMISJA BADANIA WYPADKÓW LOTNICZYCH), with the investigation supervised by Bogdan Fydrych and concluded on October 2, 2015. No fatalities or injuries were reported, and no aircraft registrations were provided in the source document. ## Operational Sequence and Separation Loss The incident took place during radar vectoring in the GAT ACC T sector. The Airbus A320 was flying straight to the MAPIK navigation point at flight level 370 (FL 370) when its crew received an instruction to turn right by 10 degrees. Simultaneously, the Airbus A321 was climbing to FL 290 after departing from LKPR. Upon joining the frequency, the A321 crew also received a 10-degree right turn instruction and clearance to climb to FL 330. Initial radar measurements showed a stable separation of approximately 7.4 NM between the two aircraft. After several minutes, with separation remaining above 7.3 NM, the A320 crew reported readiness to descend when asked about their distance to the top of descent (TOD). The A320 was then cleared to descend to FL 190 while maintaining its current heading. Both aircraft maintained relatively stable speeds during this period. Approximately 10 seconds before the closest point of approach, the measured distance dropped to 7.1 NM, prompting the controller to issue an additional 10-degree turn instruction to the A320. At the moment of closest approach, the separation measured 6.93 NM, which fell below the 7 NM minimum separation standard. Following the event, the A321 resumed its own navigation, while the A320 continued on its current heading for a period at the request of APP EPKK. ## Investigation Findings and Contributing Factors The investigation revealed that the air traffic controller (KRL) was on their second day of work, with the incident occurring just before a shift change after 1 hour and 20 minutes of duty. The controller had taken a 1.5-hour break prior to the incident. The number of open sectors was appropriate, but traffic intensity was at the upper limit of acceptable values. When the conflict was identified, the controller issued 10-degree turn instructions to both crews, which initially established a lateral separation of 7.36 NM. Subsequently, the A320 was instructed to descend to FL 190 while the A321 was cleared to climb to FL 330. The A321 maintained a constant ground speed of 513 knots, while the A320 began to accelerate slightly during its descent. This 10-knot difference in ground speed caused the separation to decrease from 7.36 NM to 6.92 NM. The investigation noted that heavy air traffic in the sector and the incident's timing near the end of the controller's duty period may have affected monitoring of this change. The controller working at the KRL EC ACC GAT position held an Area Control Service (ACS) license obtained in 2014. On the day of the incident, the controller possessed valid ACS qualifications and current medical certification. The controller's training on dangerous situations had been conducted as part of their basic course. ## Probable Cause and Preventive Actions The investigation attributed the incident to errors in air traffic management (ATM) operations. No safety recommendations were formulated by the commission. Preventive actions taken by the investigating entity included: 1. Transmitting the final report and collected materials to the Area Control OJT Training Team for presentation during training sessions and to improve controller work quality. 2. Forwarding the final report to the LSM ACC GAT to familiarize the involved controller with the report's findings, aiming to reduce the likelihood of similar incidents in the future. 3. Providing the final report and materials to the ATS Personnel Training Center for inclusion in the database of investigated incident materials used by instructors during basic and refresher training for air traffic controllers.