Two emergency slides on the Air France jet that crashed this week in Toronto malfunctioned, investigators said as they tried to determine why the plane skidded off the end of a runway at Canada's busiest airport.

The Airbus A340 failed to stop after touching down during a severe thunderstorm on Tuesday, plunging into a ravine and burning to a charred and twisted hulk. All 309 people on board survived.

Investigators are studying data from the two black boxes -- flight data and cockpit voice recorders -- recovered from the dismembered plane, and are nearly finished combing through the wreckage.

They said four of the plane's doors and emergency exits were used during the evacuation, and that experts had been brought in -- including from Goodrich, which made the slides -- to determine why two of them failed to work properly and why one door was hard to open.

"They are on-site presently with the team and they are looking at why these slides and (the door) did not work as advertised," said Real Levasseur of Canada's Transportation Safety Board.

Levasseur, who is leading a team of more than 50 from Canada and elsewhere, has said it appeared the plane touched down farther down the runway than is normal for a jet of its size.

On Saturday, he said an expert from the US Federal Aviation Administration was examining tire marks left on the runway.

Levasseur also said he had been going over eyewitness accounts of the crash. He urged people who had taken pictures of the accident to come forward.

"Sometimes you have eight reports who say the same thing and one who says something different, and the one who is different is right," he said.

He reiterated that so far there was no evidence of a mechanical failure. Investigators were waiting to interview the pilot, who was injured in the crash.

The Airbus A340-300 is one of the biggest commercial jets in service. It is 208 feet (63 metres) long, seats nearly 300, has four engines and weighs a maximum of 200 tonnes while landing.

The crash has also focused attention on Toronto's Pearson International Airport, the biggest and busiest in Canada.

The Air Line Pilots Association, which represents 64,000 airline pilots at 41 airlines in Canada and the United States, has complained about the ravine and said unobstructed "safety areas" were needed beyond the end of runways to give planes more room to stop.

"It is the latest in a series of airline accidents that highlight the dangers of inadequate runway safety areas," the association said.

Two people died in 1978 when an Air Canada plane ended up in the same ravine, which is some 100 feet (30 metres) deep.