What happened
An Air Canada Boeing 737 was operating a scheduled flight from Vancouver, British Columbia, to Whitehorse, Yukon, cruising at flight level 310. Simultaneously, an Omni Air Express DC-10 was flying southeast from Anchorage, Alaska, toward North Carolina. While the DC-10 was under the control of the Edmonton Area Control Centre (ACC) and had been cleared to climb, the B73 and the DC-10 experienced a loss of separation in non-radar airspace near the DUXAR intersection.
The conflict was identified when both aircraft received automated traffic alerts and collision-avoidance system warnings. To avoid a collision, the DC-10 descended to flight level 290, while the B737 climbed to flight level 335 before eventually returning to its original altitude once the danger had passed. There were no fatalities or injuries during the encounter.
The investigation
The investigation focused on the breakdown of multiple air traffic control defenses. It was established that the Sandspit data controller failed to follow standard marking conventions on flight progress strips, placing an estimate in a location that made the flight information indistinguishable from others. Furthermore, when passing information to the automated system (ATOS), the controller omitted the specific fix name, which prevented the system from correctly identifying that the aircraft was approaching the boundary of the Edmonton ACC.
Additionally, the investigation found that the Sandspit radar controller did not notice the B737 target disappear from the radar display due to a focus on other traffic. The handover process between the data controller and the radar controller during sector consolidation also lacked a detailed review of flight statuses, allowing the coordination errors to go undetected.
Findings
- The Sandspit data controller failed to pass the B737 estimate to the Edmonton ACC, meaning the aircraft was not activated on the Edmonton controller's display.
- The Edmonton controller was unaware of the conflicting traffic because the B737 was not properly identified in their sector.
- The failure to include the fix name when passing estimates to ATOS prevented the automated system from flagging the aircraft for transfer to the next agency.
- The radar controller did not transfer the B737 to the Edmonton frequency before the aircraft left radar coverage.
- There was a lack of specific guidance for ATOS personnel regarding how to handle rejected flight plan messages.
- The radar display lacked a compelling warning to alert controllers when a target disappeared from the screen.
Safety action
Following the incident, Nav Canada implemented new, well-defined procedures for ATOS personnel regarding the exchange of flight data and instructions for handling rejected messages. In response to a TSB safety advisory, Nav Canada also upgraded radar data-processing systems to include enhanced alerts, such as color highlighting and flashing, to notify controllers when a radar target is lost.