What to know about the plane that crashed while landing at Toronto’s airport

A passenger jet made a hard landing before it lost a wing, burst into flames and flipped onto its roof at Toronto’s airport, the fourth major aviation accident in North America in the past three weeks.

Although 21 people were injured, all 80 people on board the Delta Air Lines flight from Minneapolis survived the crash Monday.

Here are some things to know about the crash:

What caused the airplane to flip?

Investigators and airport officials have been careful to avoid talking about what went wrong when the plane touched down.

Communications between the tower at Toronto’s Pearson International Airport and the pilot were normal on approach and airport officials said Monday was a clear day with normal operations before the crash.

Were strong winds a factor in the crash?

Toronto Pearson Fire Chief Todd Aitken said the runway was dry and there was no cross-wind conditions.

Audio recordings indicate that the control tower warned the pilots of a possible air flow “bump” on the approach. Winds were gusting up to 40 mph (65 kph) during the day at the airport, according to the Meteorological Service of Canada.

But airplanes and pilots should be equipped to handle those kind of winds while landing, said John Cox, CEO of aviation safety consulting firm Safety Operating Systems in Florida.

Were the passengers badly injured?

Of the 21 people who were transported for treatment, all but two have been released from hospitals, the airport’s chief executive said Tuesday.

The two who remain in the hospital do not have life-threatening injuries, said Deborah Flint, CEO of Greater Toronto Airports Authority.

Some of those injured were exposed to leaking fuel, according to airport fire officials.

What happened inside the plane?

One passenger told told CBC News that he found himself upside down and still strapped in his seat after a forceful landing.

Peter Carlson said he crashed onto the ceiling when he took off his seat belt and smelled gas. He and another man helped a mother and her young son out of the plane before getting out.

Most of the passengers were able to begin evacuating on their own, fire officials who responded to the crash said.

Who is investigating?

The U.S. Federal Aviation Administration said the Transportation Safety Board of Canada will lead the investigation. The National Transportation Safety Board in the U.S. was sending a team to assist.

Is it safe to fly?

The fourth major aviation accident in North America in less than a month has many people concerned about the safety of flying. Fatal crashes remain rare and the track record of U.S. airlines is remarkably safe.

But there have been deadly crashes recently around the world and U.S. officials have been raising concerns about an overtaxed and understaffed air traffic control system for years

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Associated Press writers John Wawrow and Michael Casey contributed to this report.