Investigators say when they looked at the plane's engine, some parts were loose and appeared to be installed incorrectly, with one "allowing fuel to leak from the fitting."

The preliminary findings don’t identify the cause of the fire because the NTSB won’t reach that conclusion until after it completes its investigation sometime next year.

On March 13, an American Airlines flight was diverted from its destination after the flight crew reported engine vibrations, and its engine caught fire once it landed. The National Transportation Safety Board said in a report this week the engine leaked fuel because of loose and improperly installed parts.