Updated: 3:40 p.m. ET, Oct. 29, 2016

(Bloomberg) -- An AmericanAirlines jetliner caught fire while preparing for takeofffrom Chicago’s O’Hare airport, sending columns ofthick black smoke into the air as passengers fled on escapeslides.

Twenty people were taken to hospitals for treatment of minorinjuries ranging from bruises to hurt ankles, Juan Hernandez,district chief of emergency medical services for the Chicago FireDepartment, said at a news conference Friday. American set thenumber of injured at seven travelers and one flightattendant.

The Boeing Co. 767 had an engine malfunction just before thefire, said Leslie Scott, a spokeswoman for American. TheU.S.Federal Aviation Administration initially said the fireoccurred after a tire burst and later issued a statement saying itoccurred “after experiencing a problem during takeoff.”

“There was a huge explosion on the right-hand side of theairplane,” Hector Cardenas, a passenger on the plane, told the ABCtelevision affiliate in Chicago. “Everyone was sort ofpanicking.”

Charred wing

Chicago Fire Department officials declined to commenton the cause of the blaze, which might not be determined forawhile, said Timothy Sampey, assistant deputy fire commissioner forairport operations.

The plane was carrying about 43,000 pounds of fuel and there was“a substantial fuel leak,” he said at the news conference. “Therewas a heavy volume of fire on the engine and all the way to thewing tip.”

“This could have been absolutely devastating if it happenedlater,” Sampey said.

Incident investigation

The pilots aborted the takeoff, said the FAA, which willinvestigate. Flight 383, headed for Miami, carried 161 passengersand nine crew members. The NationalTransportation Safety Board also is sending three investigatorsto the scene, the agency said on Twitter.

One potential cause of jet engine explosions is a foreign objectthat gets sucked in, said BillWaldock, a professor of aviation safety at Embry-RiddleAeronautical University, comparing the powerplant to a vacuumcleaner. Issues inside the engine have also led to explosions, saidWaldock, who was speaking generally and didn’t have specificdetails about the Chicago incident.

Explosions can send shrapnel across the plane and rupture fueltanks and fuel lines, he said. In the case of a Boeing 767 orBoeing 777, much of the fuel actually is stored in the wing inwhat’s called an integral fuel tank, or “wet wing,” Waldocksaid.

FedEx plane burst into flames in Fort Lauderdale

Separately, a FedEx Corp. planeburst into flames at about 6 p.m. in Fort Lauderdale, Florida,after its landing gear collapsed following touchdown, the FAA saidin an e-mailed statement. Both pilots escaped from the plane,according to the agency.

A photograph posted on Twitter by someone waiting for a flightat Fort Lauderdale/Hollywood International showed a ballof flames rising to twice the height of the DC-10 wide-body’stail.

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