A Southwest Boeing 737 Max 8 20190312
An engine cowling on a Southwest Airlines, opens new tab Boeing 737-800 fell off on Sunday during takeoff in Denver and struck the wing flap, prompting the Federal Aviation Administration to open an investigatio Image Credit: AFP

Washington: An engine cover on a Southwest Airlines Boeing 737-800 fell off on Sunday during takeoff in Denver and struck the wing flap, prompting the Federal Aviation Administration (FAA) to open an investigation.

No one was injured and Southwest Flight 3695 returned safely to Denver International Airport around 8:15 a.m. local time (1415 GMT) on Sunday and was towed to the gate after losing the engine cowling.

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The Boeing aircraft bound for Houston Hobby airport with 135 passengers and six crew members aboard climbed to about 10,300 feet (3,140 m) before returning 25 minutes after takeoff.

Passengers arrived in Houston on another Southwest plane about four hours behind schedule. Southwest said maintenance teams are reviewing the aircraft.

The plane entered service in June 2015, according to FAA records. Boeing referred questions to Southwest.

The 737-800 is in the prior generation of the best-selling 737 known as the 737 NG, which in turn was replaced by the 737 MAX.

Southwest declined to say when the plane's engine had last had maintenance.

ABC News aired a video posted on social media platform X of the ripped engine cover flapping in the wind with a torn Southwest logo.

Here's what we know about the incident so far.

What is an engine cowling cover?

An engine cowling is a protective covering that houses an airplane engine made of metal or composite material. The cowling is part of the nacelle, which is separate from the fuselage and houses the engine and other equipment such as fuel tanks or electrical systems.

An engine cowling reduces drag, increases speed and smoothes airflow, allowing for better engine cooling and protects engine controls. Cowlings are required to be resistant to extreme temperatures and heavy vibrations.

What did southwest say?

The company said Southwest Flight 3695 returned to Denver International Airport and landed safely after experiencing a mechanical issue. "We apologize for the inconvenience of their delay, but place our highest priority on ultimate Safety for our Customers and Employees. Our Maintenance teams are reviewing the aircraft," Southwest said in a statement.

Why did the engine cowling cover fall off?

We do not know the reason this particular cover fell off.

The Seattle Times reported in 2022, opens new tab that dozens of similar accidents have happened in the past three decades on 737s and Airbus A320s but none resulted in injuries. The paper said almost every cowling incident had been traced to maintenance errors tied to a fan cowl door latching failure missed during preflight checks.

Airbus has said it developed, opens new tab several additional devices to prevent incidents including improving fan cowl latches and adding sensors.

What else has fallen off a plane recently?

In January, the door plug from a new Alaska Airlines Boeing 737 MAX 9 fell off in mid-air. The National Transportation Safety Board said four key bolts appear not to have been installed when it left the Boeing factory.

Last month, the FAA said it was investigating how a United Airlines (UAL.O), opens new tab Boeing 737-800 lost an external panel before landing safely in Oregon Friday. The FAA said a post-landing airline inspection of the 25-year-old airplane revealed a missing panel.

Those incidents appear unrelated to the cowling cover problem.

Is it safe to fly?

The last fatal US passenger airline crash occurred in February 2009 - more than 15 years ago. Transportation Secretary Pete Buttigieg said last week that air travel is the "safest form of travel in America."

What happens next?

The FAA is investigating several other recent engine issues on Southwest's fleet of Boeing planes. The FAA will conduct interviews and review maintenance records to determine what went wrong. The FAA can take enforcement actions or issue fines for airlines failing to follow safety rules.