Airline regulators in the US have begun an investigation after an engine cowling on a Boeing 737-800 fell off during take-off and struck a wing flap.

The Southwest Airlines flight returned safely to Denver International airport at about 08:15 local time (15:15 GMT) after originally departing to Houston.

The aircraft had 135 passengers and six crew members on board and rose to about 10,300 feet (3,140m) before landing.

The incident comes amid manufacturing and safety concerns at Boeing.

Southwest Airlines said its maintenance teams would review the Boeing 737-800 after its cowling, which covers the plane's engine, fell off. The airline confirmed it was responsible for maintenance of such parts.

"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 plane was manufactured in 2015 according to regulator Federal Aviation Administration (FAA) records, and the 737-800 is an earlier generation of the 737 from the latest Max model.

Both aircraft are powered by CFM56 engines – a joint venture between General Electric Aerospace and Safran Aircraft Engines.

The FAA said the Boeing aircraft was towed to the gate after landing.

Boeing declined to comment when approached by BBC News, referring questions to Southwest for information about the airline's plane and fleet operations.

Southwest said it would fly passengers on another plane to Houston about three hours behind schedule.

Boeing has been under scrutiny following a dramatic mid-air blowout in January, in which passengers on the flight from Portland, Oregon, to California narrowly escaped serious injury.

On Friday, it was announced Boeing paid $160m (£126m) to Alaska Air to make up for losses the airline suffered following the emergency.

Regulators temporarily grounded nearly 200 Boeing 737 Max 9 jets after a door plug fell from the Alaska aircraft shortly after take-off.

Boeing has been trying to repair its reputation for years after crashes in 2018 and 2019 involving a different version of the 737 Max plane killed 346 people.

Its popular 737 Max planes were subsequently grounded globally for more than 18 months.

(BBC)

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