What happened
On a flight path between Winnipeg and Calgary, an Air Canada Boeing 737, operating as ACA3697, was cleared by an air traffic controller to descend to flight level 290 near the Empress VOR. This descent was intended to prepare the aircraft for a handoff to the Calgary terminal sector. Simultaneously, a Canadian Regional Airlines Fokker F28, registered as CDR8510, was climbing through the same area toward Regina.
To maintain separation from a different westbound aircraft, the controller directed ACA3697 onto a heading nearly opposite to that of CDR8510. This maneuver brought the two aircraft within approximately 6 nautical miles of each other. The potential collision was only avoided when the traffic alert and collision-avoidance system (TCAS) issued a resolution advisory to the crew of CDR8510, instructing them to descend. The aircraft ultimately passed each other with roughly 1,300 feet of vertical separation and 1,000 feet of horizontal separation, narrowly avoiding a breach of the required 5-nautical-mile horizontal minimum.
The investigation
The investigation focused on the Alsask sector of the Calgary en route specialty within the Edmonton Area Control Centre. Investigators examined the controller's actions regarding altitude assignments and the management of multiple aircraft in the sector. The probe also looked into the technical capabilities of the radar systems in use at the time and the lack of automated conflict alerts for controllers.
Findings
- The air traffic controller lost situational awareness because their attention was preoccupied with resolving a separation issue between two other westbound aircraft.
- The controller assigned an altitude to ACA3697 that was inappropriate for the direction of flight, significantly increasing the risk of a conflict with eastbound traffic.
- Flight progress strips were not updated to indicate the inappropriate altitude or the potential for conflict.
- The controller failed to detect the converging paths of the two aircraft on the radar display.
- At the time of the incident, the radar systems in the Edmonton ACC lacked automatic conflict-alerting defenses.
- There were no standardized procedures requiring controllers to visually indicate potential conflicts on the radar display.