What happened
On a day with visual meteorological conditions, a Voyageur Airlines de Havilland DHC-7 (VAL712) was cruising at 17,000 feet en route from Masset, British Columbia, to Vancouver. Simultaneously, a Cessna 421, registered C-GKOS, departed Port Hardy for Red Deer, Alberta, climbing to 17,000 feet. As both aircraft approached the KELSY intersection—a reporting point on V3/347—their flight paths converged.
During the handoff of C-GKOS from the Nootka radar controller to the Comox terminal controller, the Comox controller noticed the close proximity of VAL712. The Nootka controller subsequently recognized the conflict and ordered C-GKOS to descend to 15,000 feet. However, by the time the instruction was processed, the aircraft had already passed one another. The two planes reached a minimum separation of only 0.8 nautical mile at 17,000 feet. The potential collision was ultimately averted because the crew of VAL712 observed the other aircraft and received a TCAS alert.
The investigation
The investigation focused on the air traffic control sequence and the breakdown in situational awareness. Investigators found that the Nootka radar controller had cleared C-GKOS to 17,000 feet without accurately assessing the converging tracks of the two flights. Although the collision geometry was visible on the radar display for approximately 12 minutes, the controller did not use available radar tools to monitor the intersection or annotate flight progress strips to indicate a potential conflict.
Furthermore, the controller's attempts to resolve the conflict were hindered by communication errors. The controller twice used the incorrect call sign when issuing instructions to C-GKOS, which delayed the pilot's response. Because the descent instruction was not issued with imperative language, the pilot of C-GKOS did not immediately recognize the urgency, and the altitude change occurred after the aircraft had already crossed paths.