WASHINGTON, April 7 (Reuters) - The U.S. Federal

Aviation Administration on Sunday said it would investigate

after an engine cowling on a Southwest Airlines Boeing

737-800 fell off during takeoff in Denver and struck the wing

flap.

Southwest Flight 3695 returned safely to Denver

International airport around 8:15 a.m. local time on Sunday and

was towed to the gate. The Boeing ( BA ) aircraft with 135

passengers and six crew members aboard had been headed to

William P. Hobby Airport in Houston.

No one was injured.

Southwest ( LUV ) said it was flying passengers on another plane to

Houston approximately three hours behind schedule. Southwest ( LUV )

said maintenance teams are reviewing the aircraft.

The plane entered service in June 2015, according to FAA

records. Boeing ( BA ) referred questions to Southwest ( LUV ) for information

about the airline's airplane and fleet operations.

The airline declined to say when the plane's engine had last

had maintenance.

ABS News aired a video posted on social media platform X of

the ripped engine cover flapping in the wind with a torn

Southwest ( LUV ) logo.

Boeing ( BA ) has come under intense criticism since a door plug

panel tore off a new Alaska Airlines 737 MAX 9 jet at

16,000 feet on Jan. 5.

In the aftermath of that incident, the FAA grounded the MAX

9 for several weeks, barred Boeing ( BA ) from increasing the MAX

production rate and ordered it to develop a comprehensive plan

to address "systemic quality-control issues" within 90 days.

Boeing ( BA ) production has fallen below the maximum 38 MAX planes

per month the FAA is allowing. The Justice Department has opened

a criminal investigation into the MAX 9 incident.

The 737-800 is an earlier generation of the best-selling 737

from the current MAX.

The FAA is investigating several other recent Southwest

Boeing engine issues.

A Southwest ( LUV ) 737 flight on Thursday aborted takeoff and

taxied back to the gate at Lubbock airport in Texas after the

crew reported engine issues. The FAA is also investigating a

March 25 Southwest ( LUV ) 737 flight that returned to the Austin

airport in Texas after the crew reported a possible engine

issue.

A March 22 Southwest ( LUV ) 737-800 flight returned to Fort

Lauderdale airport after the crew reported an engine issue. It

is also being reviewed by the FAA.