United Airlines released a statement Monday after Flight 108, bound for Munich, Germany, had to turn back. The Boeing 787 with 219 passengers and 11 crew members had to retreat to Dulles International Airport after the left engine failed.

Mayday warnings happen regularly, say aviation experts—and both pilots and air traffic controllers are trained to know what to do.

On July 25, United Airlines Flight 108 made an emergency return to its departure site, Washington Dulles International Airport, after experiencing a suspected engine failure.