What happened
At approximately 1800 Mountain Standard Time, a loss of separation occurred between an Air Canada Jazz CL600-2B19 (registration JZA227) and a Northwestern Air Lease BAE 3112 (registration PLR510) near the Yellowknife Airport. The incident took place during instrument meteorological conditions (IMC) at dusk.
The sequence began when the Yellowknife sector controller cleared JZA227 for a straight-in instrument landing system approach to runway 33. Shortly after, the Yellowknife tower advised the sector controller that PLR510 was requesting a departure from runway 15, suggesting a turn to 100° Magnetic after takeoff to facilitate the movement. The sector controller approved this departure plan.
However, a delay in the departure of PLR510 disrupted the planned separation. While the sector controller believed the aircraft was about to roll, it remained stationary at the runway threshold for over a minute. As PLR510 eventually took off and began its turn, the aircraft tracks converged. The two aircraft passed within 0.8 nm laterally and 500 feet vertically, failing to maintain the required 5 nm or 1000-foot separation.
In an attempt to resolve the conflict, the sector controller instructed both aircraft to level off at different altitudes. Due to the delay in communicating these instructions through the tower, the aircraft had already passed through the requested levels. To avoid further conflict, the pilot of JZA227 transitioned to a visual approach for runway 15.
The investigation
The investigation examined the coordination between the Yellowknife sector controller and the Yellowknife tower controllers, including the roles of the on-the-job instructor and the trainee. The TSB reviewed the adherence to the Inter-Unit Arrangement and the Air Traffic Control Manual of Operations (ATC MANOPS).
Investigators analyzed the accuracy of the information provided by the tower regarding the takeoff readiness of PLR510. They also looked into the communication loop, specifically how the relay of altitude restrictions from the sector controller to the aircraft via the tower controller contributed to the timing of the event. Furthermore, the investigation scrutinized the unauthorized transfer of control for JZA227 during its visual maneuver under IMC conditions.
Findings
- The Yellowknife sector controller failed to modify the arrival plan sufficiently to account for the departing PLR510, and did not implement safety buffers such as a cancelled time clearance.
- Inaccurate information regarding the takeoff timing of PLR510 led the sector controller to maintain a plan that was no longer viable.
- The tower controller communicated that PLR510 was rolling when it was actually still at the threshold, compromising the sector controller's situational awareness.
- The delay in relaying altitude instructions through the tower prevented the establishment of vertical separation.
- The tower controller requested and the sector controller approved the transfer of control for JZA227 during a visual approach in IMC, which was contrary to established procedures.