On 03 January 2019, a flight operated by Westjet Encore left the Calgary International Airport, Alberta enroute to Nanaimo Airport, British Columbia. At the same time, a privately registered Piaggio was travelling from Spokane International Airport, Washington, USA, to Kamloops Airport, British Columbia. Both aircraft were being provided air traffic control services from an air traffic controller at the Vancouver Area Control Centre (ACC) and were flying at Flight Level 220 (approximately 22 000 feet above sea level) prior to the occurrence.
The flight data processers (FDP) in the Vancouver ACC had undergone a software update prior to the occurrence, but previous information in the FDPs had not been purged, leading to a disparity error between the flight plan data and the radar identified flight path of the Piaggio. The controller was not familiar with such disparity errors and in his attempts to resolve the discrepancy for the Piaggio, did not identify the potential conflict between the Westjet Encore and Piaggio flight plans.
Additionally, the disparity error meant the Medium Term Conflict Detection software designed to predict traffic conflicts, and which the controller had come to rely on, was unavailable to predict the loss of separation. Traffic volume in the airspace had increased, leading to a high workload for the controller. The controller did not see or hear the visual and audible warnings as the two aircraft approached one another.
The traffic alert and collision avoidance system (TCAS) on board the Westjet Encore flight alerted the crew to decrease altitude. The pilot of the Piaggio maintained altitude and saw the Westjet Encore aircraft descending. The separation between the aircraft was reduced to 1000 feet vertically and 0.9 nautical miles laterally. Both flights continued to their destination without further incident.
The investigation also identified risks regarding controller familiarity with equipment errors, and the adequacy of controller workload monitoring by team supervisors.
Following the occurrence, NAV CANADA implemented a number of safety actions including making improvements to the checklist for completing software updates and purging flight data from FDPs. A new directive was issued to controllers regarding the minimum volume setting for audible alerts. Additional directives were issued regarding airspace sectorization to ensure that traffic levels remain manageable and appropriate supervisory oversight.
See the investigation page