Days after an older Boeing 737 engine caught on fire, there's still few answers about what led to the sparks. But aviation experts are keyed in to reports of "engine vibrations."

Ingrid Hibbitts was supposed to be headed to Argentina for a wedding on Thursday evening when her American Airlines flight turned into something “like a nightmare,” catching fire after engine problems forced an emergency landing at Denver International Airport.

Video showed people standing on a wing of the aircraft, which was evacuated using the slides. Twelve people were taken to hospitals with minor injuries, officials said.