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.

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.

A fuel leak and several improperly installed parts were found inside the engine of an American Airlines plane that caught fire after the plane landed in Denver in March, according