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.

Delta Air Lines has faced a series of unsettling incidents over the past week, including smoke or haze in the cabin on two flights and a separate crash that injured more than 20 people.

A Delta flight that had just taken off from Boston Logan International Airport had to quickly return after a "smoky odor" was detected in the cabin shortly after takeoff, the airline said.