Congestion at Canada's busiest airport appeared to ease Sunday afternoon as the skies cleared and service resumed on a runway that was closed earlier in the day.
Flight cancellations at Toronto's Pearson International Airport seemed to dwindle by late afternoon, though the airport's website showed delays stretching well into the evening.
The runway had been closed after a fire in a maintenance area on the airfield damaged electrical systems required to operate runway lights.
In the morning's low visibility, the runway couldn't be used without sufficient lighting.
The closure of one of the airport's five runways, combined with the heavy fog, caused widespread flight delays and cancellations as the airport's capacity for arrivals and departures was reduced.
The runway was back in service just before 11 a.m. after the fog lifted.
Scott Armstrong, a spokesman for the Greater Toronto Airport Authority, said electricians were working to fix the damaged lighting system with the airport aiming to have the runway lights working by late afternoon.
He warned, however, that the ripple effect of this morning's delays and cancellations will continue for some time.
"There will be delays throughout the day, there will be cancellations throughout the day and people just need to be aware the things will be slower," he said.
"What you see is delays in flights, but also you see the airlines make adjustments in their schedules. So they may decide to cancel one flight and consolidate. So instead of two flights going out to Montreal for example, they'll put all the passengers on one flight and send out one full plane."
Mr. Armstrong urged all travellers to double-check their flight status before heading to the airport.
The disruptions in Toronto came as thousands of March Break travellers were heading home.
Air Canada, which cancelled a number of flights out of Toronto, said it had to scrap or delay several flights as a result of the "significant reduction" in runway operations Sunday morning.
"Although restrictions have been relaxed, earlier this morning the GTAA was allowing only 12 aircraft movements at the airport versus 50 or more normally," said spokesman Peter Fitzpatrick. "As a result we had to cancel and delay a number of flights this morning."
It's been a trying weekend for some Canadian air travellers.
Several Air Canada flights were also cancelled or delayed in Montreal on Saturday, prompting the airline to say it was facing a number of "operational challenges."
CTV News had reported those cancellations were due to some pilots calling in sick because of stress or fatigue. The network attributed the information to unnamed sources.
Mr. Fitzpatrick did not directly confirm or deny the reports, it was not clear whether sick-calls may have also contributed to the delay problem in Toronto Sunday.
Air Canada is in the middle of a bitter labour dispute with its pilots that prompted the federal government to step in earlier this month.
In the face of a threatened lockout by pilots and a strike by ground crew, the federal government referred the matter to the Canada Industrial Relations Board and also passed back-to-work legislation last week that referred the disputes to arbitration.