An inquiry into how an Air France jet burst into flames after skidding off a runway in Toronto could take months or years, air investigators have warned.
Flight data and voice recorders have been recovered from the wreckage of the Airbus A340, which crashed in bad weather on Tuesday.
Air investigators hope the so-called black boxes will hold vital clues.
All of the 309 passengers and crew escaped, in what Canada's transport minister has called a "miracle".
Some 43 people were injured in the accident.
Investigators have been clambering over the blackened shell of the plane, which is believed to have broken up into three large chunks.
The two flight records retrieved from the cockpit have now been sent for analysis.
There are several theories about what happened as the plane from Paris landed amid thunder and lightning at 1603 local time (2003 GMT).
After touching down on the runway, it lurched across the wet tarmac before skidding towards the airport perimeter.
The plane overshot the runway by about 200m (660ft) and came to rest with its tail pointing in the air in a shallow ravine next to Canada's busiest motorway, Highway 401.
Moments after the last survivor clambered away from the jet, the fuselage was engulfed in smoke and flames.
One theory is that water accumulated on the runway, causing the aeroplane to lose traction.
Another idea is that a strong head wind forced the aircraft off course around the time of the landing.
The chief Canadian investigator promised to look at every possibility, and warned that these kind of accidents are seldom the result of a single cause.
But Real Levasseur questioned the suggestion that lightning was responsible for Tuesday's accident.
"We've had many cases of aircraft that have been hit by lightning and it's normally not a problem," he said.
The chairman of Air France has also arrived to survey the wreckage.
Jean Cyril Spinetta praised the flight crew and defended the working order of the plane, which entered service in 1999.
"When it left Paris it was in perfect working order," he said.
It is the first major crash for an Airbus A340-300 since the model's debut flight in October 1991.
The plane was last inspected on 5 July.
It had flown 28,418 flight hours across a total of 3,711 flights.