What happened
On 14 October 2016, a DHC-8-400 operated by Porter Airlines, registered C-GKQA, was performing a scheduled flight from Toronto/Billy Bishop Toronto City Airport to Sudbury, Ontario. As the aircraft approached Sudbury from the south, the crew was cleared for a visual approach to Runway 04.
Simultaneously, another DHC-8-400 operated by Jazz Aviation, registered C-GXJZ, was departing from Sudbury on Runway 22. Radar monitoring revealed that while both aircraft were at an altitude of approximately 4000 feet and roughly 8 nautical miles southwest of the airport, they reached a separation distance of only 0.4 nautical miles.