What happened
On 24 April 2009, a Canadian Forces Canadair CL600, registration CC144618, was climbing through flight level 370 while en route from Vancouver to Ottawa. Simultaneously, a United Arab Emirates Boeing 777-200LR, registration A6-EWA, was cruising at the same altitude on a flight from Dubai to Los Angeles.
While operating near Penticton, British Columbia, an automated radar conflict alert notified the controller that the two aircraft would violate the required five nautical mile separation within one minute. The controller instructed the CC144618 to descend to flight level 360 and requested turns for both aircraft. While the A6-EWA crew responded to a TCAS resolution advisory by climbing, the aircraft eventually closed to within 500 feet of vertical separation, failing to maintain the mandatory 1000-foot vertical buffer.
The investigation
The investigation examined the actions of the Vancouver Area Control Centre controller and the effectiveness of the conflict alert system. It was established that the controller had identified the potential conflict early in the shift. The controller intended to reroute the A6-EWA to a westerly track and subsequently climb it to flight level 380. However, the controller did not complete the routing change or issue the climb instruction, and the controller's attention subsequently shifted to other traffic.
Investigators also reviewed the use of flight progress strips and communication protocols. The controller did not use the required red "W" notation on the flight progress strips, which serves as a critical reminder that a conflict remains unresolved. Furthermore, the investigation looked into the timing of the aircraft's maneuvers and the adequacy of the 60-second warning provided by the conflict alert system.
Findings
- The controller identified the conflict early but failed to use a required aide-memoire to ensure the resolution was completed.
- The controller did not utilize imperative phraseology, which likely delayed the flight crews' response to the instructions.
- The specific turn instructions issued to both aircraft were ineffective at maintaining the required lateral separation, resulting in one aircraft flying directly over the other.
- The 60-second window provided by the conflict alert system may be insufficient to resolve conflicts when decision-making delays or slow crew responses occur.