WATCH: Boeing 737-800 plane engine cover falls off during takeoff in US

The Southwestern Airlines aircraft rose to 10,300 feet and was forced to return to the Denver International Airport, where it made a safe landing

The engine cover of a Boeing 737-800 plane, headed to Houston with 135 passengers and six crew members on board, fell off during takeoff and struck its wing.

The aircraft, part of the Southwestern Airlines fleet, rose to 10,300 feet and was forced to return to the Denver International Airport. The aircraft landed safely, and was towed to the gate. No one was injured in the incident. The passengers arrived in Houston on another Southwest plane, four hours behind schedule. Southwest Airlines said that maintenance teams are reviewing the aircraft involved in the incident.

The Federal Aviation Administration (FAA) has started an investigation into this incident. The FAA found that the plane had entered service in June 2015. However, the airline refused to share details on when the plane's engine was last serviced.

A video of the incident on social media shows the ripped engine cover flapping in the wind as the crew lands the aircraft.
 

A passenger said, "People in the exit row across from me started yelling at the flight attendants and showing them the damage. We turned around and made a full-speed landing. The pilots did a great job on the landing."

According to radio transmissions with an air traffic controller, the crew declared an emergency as soon as they noticed the flapping cover. "Let's go ahead and declare an emergency for Southwest 3695 and we'd like an immediate return. We've got a piece of the engine cowling hanging off," a crew member said.

The incident comes amid safety concerns at Boeing, which started with an emergency on an Alaska Airlines flight on January 5 this year, in which a panel blew off a new Boeing 737 Max 9, delivered to the airline just months earlier. Following the incident, the FAA grounded the Max 9 for several weeks and barred Boeing from increasing the Max production. The authorities asked Boeing to develop a comprehensive plan to address "systemic quality-control issues" within 90 days.

Last month, a United Airlines Boeing jet was evacuated in Houston after veering off the runway, and 50 people were injured on a New Zealand-bound Boeing jet that plummeted into a nosedive.

On March 25, a Southwest 737 flight returned to the Austin airport after the crew reported a possible engine default. In a separate incident, the Southwest 737-800 flight returned to Fort Lauderdale airport in Florida on March 22 after the crew reported an engine issue. The FAA is currently investigating these incidents as well.