A probe has been started after an engine cover fell off a Southwest Airlines Boeing 737 on a US domestic flight.
The US Federal Aviation Administration confirmed an investigation into the incident involving a Boeing 737-800 yesterday (Sunday).
The flight returned safety to Denver after the crew reported the engine cowling fell off during take off and struck the wing flap, the FAA said.
The aircraft was heading to Houston with 135 passengers and six crew on board.
On landing, the aircraft was towed to the gate.
Southwest Airlines said its maintenance teams would review the Boeing 737-800, which was manufactured in 2015.
“We apologise for the inconvenience of their delay, but place our highest priority on ultimate safety for our customers and employees,” a statement said.
The aircraft is an earlier generation of 737 from the latest Max models.
Boeing currently faces scrutiny from regulators after a panel blew out from an Alaska Air B737 Max 9 flight from Portland in Oregon in January.
The manufacturer last week disclosed that it had paid an initial $160 million to the airline to cover lost first quarter profits as a result of the incident.