A Delta Air Lines flight to Columbia, South Carolina, was forced to return to Hartsfield-Jackson Atlanta International Airport on Monday morning after a “haze” was observed inside the plane, according to officials.

Delta Flight 014 from Atlanta to Frankfurt turned back shortly after takeoff Friday night because of a mechanical issue with one of the plane’s engines, the airline said in a statement. “The aircraft landed safely and was met by firetrucks, which sprayed down the aircraft’s brakes due to the heavier than normal landing weight,” Delta said.