News release

In its investigation report (A18Q0069) released today, the Transportation Safety Board of Canada (TSB) found that short staffing and a deviation from standard procedures by air traffic controllers led to a May 2018 loss of separation between an Air Transat Airbus A310 and a Cessna 421 light twin-engine aircraft near the Montreal/Pierre Elliott Trudeau International Airport.

On 16 May 2018, both aircraft were inbound to land at the Montreal/Pierre Elliott Trudeau International Airport. The Airbus was coming from the west and was to fly north of the airport and land on Runway 24R, while the Cessna was inbound from the northeast and was to land on Runway 24L. A loss of separation between the two aircraft occurred when both aircraft were approximately 18 nautical miles northeast of the airport. At the closest point, the two aircraft came within 500 feet vertically and 1.7 nautical miles laterally of each other. Normally the aircraft should be separated by at least 1000 feet vertically or 3 nautical miles laterally.

Although seven controllers and a shift supervisor would have normally been scheduled to work that evening, absences and illness reduced that number to three controllers and a supervisor. As a result, six sectors of airspace normally divided among the controllers needed to be combined and controlled by just three—which in turn increased each of their areas of responsibility, as well as their workload and its complexity.

The TSB's investigation also found that, with the Cessna approaching from a sector to the northeast, control responsibility for it was not transferred to the next sector according to standard procedure. As a result, a controller-in-training responsible for the receiving sector, was not initially aware of the presence or intentions of the Cessna until it entered his airspace, and as a result did not have an opportunity to develop a plan to deal with the converging traffic. Also during this time, the instructor, who was both the shift supervisor and responsible for the trainee, was distracted by other tasks and wasn't able to accurately monitor the developing situation.

Shortly thereafter, the controller-in-training noticed the Cessna on the display and the required separation was re-established. Both aircraft then landed without incident.
The Board is not aware of any safety action taken following this investigation.

See the investigation page for more information.