An engine cover on a Southwest Airlines Boeing 737-800 fell off on Sunday during takeoff in Denver and struck the wing flap, prompting the U.S. FAA to open an investigation.

No one was injured and Southwest Flight 3695 returned safely to Denver International Airport around 8:15 a.m. local time on Sunday and was towed to the gate after losing the engine cowling.

The Boeing aircraft bound for Houston Hobby airport with 135 passengers and six crew members aboard rose to an elevation of about 10,300 feet (3,140 m) before returning 25 minutes after takeoff.