Dozens of passengers were forced to stand on the wing of an American Airlines plane at Denver International Airport as they evacuated the aircraft after one of its engines caught fire Thursday evening,

Two investigators from the National Transportation Safety Board were already at work Friday to look into the fire that appeared after American Airlines flight 1006 arrived in Denver the evening before.

The Federal Aviation Administration confirms a flight from Boston to Denver had to turn around and return to Logan Airport due to mechanical issues mid-flight.

A JetBlue plane was forced to return to Boston’s Logan International Airport midflight on Tuesday due to a possible issue with the aircraft. Flight 2393 to Denver turned back for Logan after there were “indications of a potential hydraulics issue,” an airline spokesperson told Boston 25 News.

The plane returned to Boston after “indications of a potential hydraulics issue,” JetBlue said in a statement.