What happened
On an unnamed date, two large aircraft flying on parallel tracks entered Canadian airspace over Baffin Island, Nunavut, separated by 60 nautical miles. The first aircraft, a Boeing 747-200 operating as British Airways Flight BAW49, was traveling from London, United Kingdom, to Seattle, USA, at flight level 330. The second aircraft, an Airbus A340-300 operating as Air Canada Flight ACA845, was flying from Frankfurt, Germany, to Calgary, Alberta, at flight level 350.
To maintain vertical separation from northbound traffic, the controller intended to climb BAW49 to flight level 3ually 350. However, to prevent a lateral conflict with ACA845 at that altitude, the route for ACA845 had to be amended first. While the amended routing was issued, the two aircraft eventually came within approximately 7 nautical miles of each other at the same flight level, violating the required 20-nautical-mile lateral separation standard.
The investigation
The investigation focused on the procedural control environment within the Edmonton Area Control Centre (ACC) north high specialty. In this region, aircraft are separated using non-radar, procedural standards based on assigned routes and altitudes. The investigation examined the Northern Airspace Display System (NSiT), a tool used by controllers to track aircraft positions and project routes.
Several technical and operational challenges were identified. The communication process relies on remote radio specialists in North Bay, Ontario, which introduces delays. Furthermore, the NSiT software lacks a route conformance check, meaning it does not automatically alert controllers if an aircraft deviates from its filed path. The investigation also looked into the voice switching communication system, noting that the inability to control volume levels independently for different communication inputs could lead to certain transmissions being masked by louder ones.
Findings
- The Nunavut controller failed to include the 60N110W waypoint when issuing the amended clearance to the Arctic radio specialist.
- The controller's attention was likely diverted by high workloads, a loud VHF radio transmission during the readback, and the physical interruption of a new flight progress strip being printed.
- The Franklin data controller did not notice that the aircraft's position report omitted the required waypoint, missing an opportunity to correct the route.
- The second Franklin controller also failed to identify the routing discrepancy, partly because the NSiT system does not differentiate between mandatory and computer-generated waypoints on flight strips.
- The lack of a route conformance check in the NSiT system increased the risk of the separation loss.
- Communication delays and the necessity of adjusting master volume levels to hear external interphone calls increased controller workload and distraction.