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 National Transportation Safety Board found a fuel leak and several improperly installed parts inside the engine of an American Airlines plane that caught fire after the plane landed in Denver in March.

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.