A Houston-bound Boeing 737-800 plane operated by Southwest Airlines returned safely to Denver International Airport on Sunday after an engine cover fell off and struck the wing flap, according to the Federal Aviation Administration.

The agency said it will investigate.

In recorded air traffic control audio, one of the pilots said that “several passengers and flight attendants heard something loud hit the wing.”

In a statement to CNN, Southwest said passengers would take another plane to Houston and would be approximately three hours behind schedule.

“We apologize for the inconvenience of their delay but place our highest priority on ultimate Safety for our Customers and Employees,” the statement said. Southwest said no injuries were reported.

Southwest said its maintenance teams would review the aircraft, which departed at 7:49 a.m. local time and returned at 8:15 a.m. The flight reached an altitude of about 10,000 feet.

The plane was deemed airworthy in May 2015, per FAA records.

Boeing declined to comment and referred CNN to Southwest for information about plane and fleet operations.

This is the latest in a string of mechanical issues to plague Boeing aircraft across a range of airlines over the past several months even as the company has faced years of scrutiny regarding the safety of its planes.

This story has been updated with additional information.

Eva Rothenberg, Sarah Dewberry and Chris Boyette contributed to this report

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