The plane was en route to Dallas from New York’s LaGuardia Airport but diverted to Philadelphia International Airport during the incident at around 11am local time this morning.
Mr Sumwalt confirmed this is the first passenger fatality on a US airline since 2009.
Philadelphia Fire Commissioner Adam Thiel said seven others aboard the aircraft were treated for minor injuries.
Television images showed most of the outer casing around the left engine of the Boeing Co 737-700 had ripped away and a window near the engine on the plane’s left side was missing.
In a phone interview with CNN, passenger Marty Martinez said a window exploded mid-flight, causing a woman serious injuries.
Mr Martinez said: “The injured woman’s arms and body were sucked toward the opening in the plane.
“Objects flew out the hole where the window had been, and passengers right next to her were holding onto her.
“And meanwhile, there was blood all over this man’s hands. He was tending to her.
“We could feel the air from the outside coming in, and then we had smoke kind of coming in the window.
“Meanwhile, you have passengers that were in that aisle, trying to attend to the woman that was bleeding from the window explosion.
“That was just chaos all around.”
Mr Martinez streamed a brief Facebook Live video with the caption “Something is wrong with our plane! It appears we are going down! Emergency landing!! Southwest flight from NYC to Dallas!!”
He said he was sitting two rows behind the window that was broken mid-flight.
“Her [the woman’s] arms and her body were sucked, like sucked in that direction, from my vantage point,” he said.
“So you see people, from the back of the seat, holding onto her, you know, trying to keep her contained.”
He said other passengers were trying to patch the hole in the plane.
“People in the other rows are – just trying to plug the hole, which sounds ridiculous, because you know people are using jackets and things, and it’s just being sucked right out,” he told CNN.
The Fire Commissioner of Philadelphia, when asked by reporters if SW Airlines 1380 was in a “free fall” as described by some passengers on social media, referred the question to the NSTB but added during an emergency landing descent “happens in a fairly rapid manner”.
Flight information provided by FlightRadar24 showed the plane went from approximately 30,000 feet to 13,000 feet in five minutes.
The entire descent took approximately 15 minutes.
Depressurisation is believed to have caused the woman to be sucked through the broken window.
“One passenger, a woman, was partially drawn out towards the outside of the plane and was pulled back in by other passengers,” Todd Baur, the father of one passenger said.
FOOTAGE OF SOUTHWEST PLANE ON THE TARMAC AFTER MAKING EMERGENCY LANDING
Southwest Airlines said: “We are deeply saddened to confirm that there is one fatality resulting from this accident.
“The entire Southwest Airlines Family is devastated and extends its deepest, heartfelt sympathy to the customers, employees, family members and loved ones affected by this tragic event.
“We have activated our emergency response team and are deploying every resource to support those affected by this tragedy.”
America’s National Transportation Safety Board has launched an investigation.
The aircraft’s maker, Boeing, said on Twitter it was aware of the incident and was “gathering more information”.
The plane’s engines are made by CFM International, a French-US venture co-owned by Safran and General Electric, which was not immediately available for comment.
https://get.convrse.media/?url=https%3A%2F%2Fwww.mirror.co.uk%2Fnews%2Fus-news%2Fsouthwest-airlines-plane-engine-dead-12381458%3Futm_source%3Dmirror_newsletter%26utm_medium%3Demail%26utm_content%3DEM_MirrorNews_BreakingNews_Button1%26utm_campaign%3Ddaily_newsletter&cre=bottom&cip=42Today’s fatality marks the first fatal accident involving a commercial US passenger airline flight in nine years.
The last deadly accident on a US passenger plane was in February 2009, when Colgan Air 3407 crashed in wintery conditions while on approach in Buffalo, killing 49 aboard and one person on the ground