A Southwest Airlines flight safely returned to Denver International Airport on Sunday after the engine cover of a Boeing 737-800 fell off during takeoff and struck the wing flap, the Federal Aviation Administration said.

Flight 3695 was headed to Houston but returned to the Denver airport around 8:15 a.m. after the crew reported the engine cowling, or cover, fell off.

The plane, which had 135 passengers and five crew members, was towed back to the gate. The F.A.A. said it would investigate.

In a statement, Southwest Airlines said its maintenance teams were reviewing the aircraft. Southwest said the passengers boarded another plane and arrived at William P. Hobby Airport in Houston 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.

A video taken from a window near the plane’s wing posted on social media showed a blue cowling peeling off the engine and twisting in the wind as the plane moved down a runway before a large portion of it eventually fell off.

“Let’s go ahead and declare an emergency for Southwest 3695 and we’d like an immediate return,” a crew member said, according to radio transmissions with an air traffic controller. “We’ve got a piece of the engine cowling hanging off.”

The incident happened during a time of increased scrutiny about other commercial air travel episodes, starting with the harrowing Jan. 5 emergency on Alaska Airlines Flight 1282 in which a panel known as a door plug blew off a new Boeing 737 Max 9, delivered to the airline just months earlier.

No one died but it triggered investigations into Boeing’s Max 9 and raised questions about quality control problems in its plane production.

Then came a string of eight episodes last month involving United Airlines aircraft in a two-week span.

Maintenance issues, loose tires and missing panels were among the issues afflicting six Boeing and two Airbus jets. A safety expert said such cases were typical and were being “falsely conflated with Boeing’s troubles.”