The Globe and Mail reports in its Tuesday edition that staffing shortages at Canada's air-traffic control agency caused hundreds of weekend flights to be cancelled at the country's two biggest airports. The Globe's Eric Atkins writes that Toronto Pearson had a total of 446 departing flights delayed and 73 cancelled on Saturday and Sunday, while Vancouver International had 204 delays and 15 cancellations. Both airports pointed the finger at Nav Canada, the country's air-traffic controller, as the peak travel season begins. Nav Canada spokesperson Maryam Amini said "unplanned absences" of air-traffic controllers caused the delays, and the agency is working to bolster its work force. The delays cascaded throughout the network, although it is not known how many stemmed from Vancouver or Toronto. Montreal Trudeau International had several flights delayed, owing to bad weather on the East Coast -- not Nav Canada constraints. At Calgary International, 23 per cent of departing flights were delayed on Saturday. "Nav Canada has instituted a ground delay program at YYZ today," Pearson said in a tweet on Saturday. Vancouver blamed "constraints within the Nav Canada air navigation system" for the delays and cancellations.