What happened
On a morning in May, two Porter Airlines Inc. Bombardier DHC8-402 aircraft experienced a near-miss southeast of the Toronto/Billy Bishop Toronto City Airport. The first aircraft, C-FLQY, was operating an instrument flight rules (IFR) flight and had been cleared for a visual approach to Runway 0SB. Simultaneously, a second Bombardier DHC8-402, registration C-GLQX, was departing the same runway on an IFR flight with a request for a visual flight rules (VFR) departure.
At approximately 0839 Eastern Daylight Time, the two aircraft crossed paths approximately 300 feet apart vertically. The incident occurred when the aircraft were roughly 6 nautical miles southeast of the airport. Both flight crews were forced to respond to resolution advisories from their respective traffic collision-avoidance systems (TCAS).
The investigation
The investigation focused on the air traffic services provided by Nav Canada at the Toronto Area Control Centre (ACC). At the time of the event, the satellite controller was managing combined sectors, which increased the complexity of the workload. The investigation established that the controller was also providing instruction to a trainee, further dividing their attention.
Investigators examined the clearances issued to both aircraft. While the departing aircraft, C-GLQX, had requested a VFR departure to expedite traffic, the arriving aircraft, C-FLQY, had been granted an unrestricted visual approach. The investigation found that the controller failed to maintain an accurate mental model of the conflicting flight paths. Furthermore, the controller's recent history of chronic sleep deprivation—averaging only six hours of sleep per night for five months—was identified as a significant factor affecting cognitive processing and working memory.