An engine on a Southwest Airlines flight with 149 people aboard exploded and broke apart in mid-air on Tuesday, killing one passenger and nearly sucking another out of a shattered window, according to airline and federal authorities and witness and media accounts.

The plane, a Boeing 737-700 which was bound to Dallas from New York, made an emergency landing in Philadelphia.

The death of 43-year-old Jennifer Riordan on Flight 1380 was the first in a US commercial aviation accident since 2009, according to National Transportation Safety Board (NTSB) statistics.

NTSB Chairman Robert Sumwalt told an evening news conference at the Philadelphia airport that a preliminary investigation found an engine fan blade missing, having apparently broken off, and that there was metal fatigue at the point where it normally attached.

Sumwalt said part of the engine's covering, called a cowling, was found in Bernville, Pennsylvania, about 70 miles from the Philadelphia airport.

"It is very unusual so we are taking this event extremely seriously," Sumwalt said. "This should not happen and we want to find out why it happened so that preventative measures can be put in place." He said the investigation could take 12 to 15 months to complete.

Flight 1380 took off from New York's LaGuardia Airport at around 10:27 am and was diverted to Philadelphia just under an hour later, according to flight tracking website FlightAware.com.

Southwest Chief Executive Officer Gary Kelly said the flight landed at Philadelphia International at around 11:20 am

The engine on the plane's left side threw off shrapnel when it blew apart, shattering a window and causing rapid cabin depressurization that nearly pulled a female passenger through the hole, according to witness accounts and local news media reports.

"We have a part of the aircraft missing, so we're going to need to slow down a bit," the plane's captain, Tammy Jo Shults, told air traffic controllers in audio from the cockpit released on NBC News.

Asked by a controller if the jet was on fire, Shults said it was not, but added, "They said there is a hole and someone went out."

"A woman was partially, was drawn out of the plane and pulled back in by other passengers," Todd Bauer, whose daughter was on the flight, told the NBC affiliate in Philadelphia.

Riordan was a Wells Fargo banking executive and well-known community volunteer from Albuquerque, New Mexico, according to a Wells Fargo official, who spoke on condition of anonymity as she was unsure whether all of Riordan's family had been notified of her death.

Riordan was on the way back from a New York business trip, where she had sent a tweet on Monday showing the view from her hotel in Midtown Manhattan with the caption: "Great business stay." Her Facebook page shows she was married with two children.

The plane, which was bound for Dallas Love Field, had been inspected as recently as Sunday, according to Southwest's Kelly, who confirmed that Tuesday's fatality was the first of its kind in the carrier's 51-year history.

At 11:18 am, passenger Marty Martinez posted on Facebook a live video of himself on the plane, wearing a breathing mask, as the plane descended. More than an hour later, at 12:27 pm, Martinez posted pictures of a blown-out window and the badly damaged engine.

ULTRASONIC INSPECTIONS

Southwest Airlines said it was accelerating its existing engine inspection program and conducting ultrasonic inspections of fan blades of the CFM56 engines on all of its the 737 jets.

In 2017 the Federal Aviation Administration issued a proposed airworthiness directive on the engine after an uncontained engine failure on a Southwest flight in August 2016. “What we want to do is see if anything in that airworthiness directive that came out from an event two years ago involving another Southwest airplane landed in Pensacola, we want to see if this part might have been subjected to that airworthiness directive,” Sumwalt said.

"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," Southwest said in a statement.

There were 144 passengers and five crew members aboard the flight.

One passenger was taken to a hospital in critical condition and seven people were treated for minor injuries at the scene, Philadelphia Fire Department spokeswoman Kathy Matheson said. Matheson could not confirm how the passenger in critical condition sustained her injuries.

Flight 1380 was diverted to Philadelphia for an emergency landing after crew members reported damage to an engine, the fuselage and at least one window, the Federal Aviation Administration said.

"YELLING AND SCREAMING"

"Everybody was going crazy, and yelling and screaming," passenger Martinez told CNN.

Martinez said objects flew out of the hole where the window had exploded, and "passengers right next to her were holding onto (the woman being pulled out). And, meanwhile, there was blood all over this man's hands. He was tending to her."

Television images showed that most of the outer casing around the left engine of the Boeing Co 737-700 ripped away and a window near the engine on the plane's left side was missing.

"All of a sudden, we heard this loud bang, rattling, it felt like one of the engines went out. The oxygen masks dropped," passenger Kristopher Johnson told CNN. "It just shredded the left-side engine completely. ... It was scary."

Southwest shares fell more than 3 percent after the NTSB reported the fatality, before closing down 1.1 percent at $54.27 on the New York Stock Exchange.

Boeing in a statement extended its condolences to the family of the woman killed, and said it is "providing assistance at the request and under the direction" of the NTSB.

The Boeing 737 is the world’s most-sold aircraft and its engines - supplied by a joint-venture co-owned by General Electric and France’s Safran called CFM International – are the most widely used in the aircraft industry and are reported to be among the most reliable.

Any design issues with the long-established CFM56 engine could have repercussions for fleets worldwide. But given that thousands of the engines are already in use globally, industry experts say the focus of the investigation is more likely to fall on one-off production or maintenance issues, though it is too early to say what caused the explosion.