Air Canada is defending a disruptive shutdown last week at Toronto's Pearson Airport due to a deep-freeze that swept much of the continent.

Chief financial officer Michael Rousseau told an analyst conference Thursday that the airline stopped flights into Canada's busiest airport because the ground was like a skating rink caused by flash freezing as temperatures quickly dropped well below zero following a rain storm.

It also supported a rare "ground stop" that was subsequently issued by Pearson's operator, the Greater Toronto Airport Authority.

With flights backed up, Rousseau said Air Canada decided to stop flying into Toronto to avoid leaving passengers stranded on the tarmac for four or five hours.

A review of that decision is underway, but Rousseau said the big question is why there was so much ice on the tarmac that a typical 20-minute airplane towing took 90 minutes.

WestJet Airlines (TSX:WJA) also said it supports the GTAA's "unprecedented" decision that has drawn scrutiny by the federal government.

The decision to halt all North American flights for more than eight hours after temperatures plummeted to -40C with the wind chill stranded thousands of passengers.

WestJet CFO Vito Culmone told the AltaCorp Capital conference that safety is the top priority and the Calgary-based airline vowed to work with other airlines and the airport operator on improvements.

On Wednesday, WestJet issued a news release saying it supports the review by an ad hoc committee of the GTAA board of directors.

Both carriers flew in additional planes to ease the backlog caused by the delays, which WestJet says affected some 22,000 of its passengers travelling to or from the airport.

Air Canada added roughly 5,000 more seats in the following days, while WestJet chartered a Boeing 747 jumbo jet and another plane to transport nearly 500 WestJet customers and 1,000 bags to Calgary.

The airport chairman apologized Wednesday for the disruptions.

Vijay Kanwar says the ground stop was instituted for the safety of employees, passengers and the public and was carefully considered and reviewed with the GTAA's partners.