A prelimary examination of the blown jet engine of the Southwest Airlines plane that set off a terrifying chain of events and left a businesswoman hanging half outside a shattered window showed evidence of "metal fatigue".
According to the National Transportation Safety Board, one of the engine's fan blades had separated from the point where it joined the rotating hub before bursting through containment measures, sending debris spearing into the body of the aircraft.
Passengers scrambled to save the woman from getting sucked out the window that had been smashed by debris. She later died, and seven others were injured.
The pilots of the twin-engine Boeing 737 bound from New York to Dallas with 149 people aboard put he aircraft into a dive in order to provide breathable air for passengers before making an emergency landing in Philadelphia.
Oxygen masks dropped from the ceiling and passengers said their prayers and braced for impact.
"I just remember holding my husband's hand, and we just prayed and prayed and prayed," said passenger Amanda Bourman, of New York.
The dead woman was identified as Jennifer Riordan, a Wells Fargo bank executive and mother of two from Albuquerque, New Mexico. The seven other victims suffered minor injuries.
A piece of the engine was later found nearly 100km away on the ground in Pennsylvania.
In a late night news conference, NTSB chairman Robert Sumwalt said the number 13 fan blades was separated and missing from the engine. The blade broke off from the point where it would come into the hub and there was evidence of metal fatigue, Sumwalt said.
High resolution photographs of the break-point have already been sent to laboratories for analysis.
The engine will be examined further to understand what caused the failure. The investigation is expected to take 12 to 15 months.
Photos of the plane on the tarmac showed a missing window and a chunk gone from the left engine, including part of its cover.
"There's a ring around the engine that is meant to contain the engine pieces when this happens," said John Goglia, a former NTSB member. "In this case it didn't. That's going to be a big focal point for the NTSB - why didn't (the ring) do its job?"
As a precaution, Southwest said Tuesday night that it would inspect similar engines in its fleet over the next 30 days.
The jet's CFM56-7B engines were made by CFM International, jointly owned by General Electric and Safran Aircraft Engines of France. CFM said in a statement that the CFM56-7B has had "an outstanding safety and reliability record" since its debut in 1997.
Last year, the engine maker and the Federal Aviation Administration instructed airlines to make ultrasonic inspections of the fan blades of engines like those on the Southwest jet. The FAA said the move was prompted by a report of a fan blade failing and hurling debris. A Southwest spokeswoman said the engine that failed Tuesday was not covered by that directive, but the airline announced it would speed up ultrasonic inspections of fan blades of its CFM56-series engines anyway.
In 2016, a Southwest Boeing 737-700 blew an engine as it flew from New Orleans to Orlando, Florida, and shrapnel tore a 5-by-16-inch hole just above the wing. The plane landed safely. The NTSB said a fan blade had broken off, apparently because of metal fatigue.
PASSENGERS SPEAK OF HORROR ORDEAL
American man Matt Tranchin, who spoke to 3AW Radio Melbourne a short time ago, said after the engine exploded there was "sheer panic" on board.
"As soon as the explosion happened the oxygen mask dropped and imagine that.
"There was a tremendous amount of blood.
"To make matters worse, there really wasn't any instruction. There was a lot of just panic and confusion. I will say the pilot did an incredible job through it all. We landed and it was as soft as you would think a landing like that could even be. We were incredibly thrilled that we had the pilot that we had, but it was sheer panic throughout the entire experience."
Mr Tranchin said the noise from the broken window was 'extremely loud', as he texted his wife from the plane to say his goodbyes.
"I couldn't feel the suction, but it became extremely loud and I think seeing the ashes whip around you was a reminder of just how precarious the situation was," he said.
"The next 20-25 minutes telling my wife and my parents I loved them and what I wanted them to pass on to my unborn son.
"You never want to scare your loved ones unnecessarily but you also don't want to pass up the opportunity to say goodbye. So I took that opportunity."
Todd Baeur, father of one of the passengers, said: "One passenger, a woman, who was partially drawn out of the plane … was pulled back in by other passengers."
Bourman told AP that she saw emergency medical workers using a defibrillator to help a woman who was taken off the plane after it landed.
Going back to the beginning, she was asleep near the back when she heard a loud noise and oxygen masks dropped.
"Everybody was crying and upset," she said. "You had a few passengers that were very strong, and they kept yelling to people, you know, 'It's OK! We're going to do this!'
"I just remember holding my husband's hand, and we just prayed and prayed and prayed. And the thoughts that were going through my head of course were about my daughters, just wanting to see them again and give them a big hug so they wouldn't grow up without parents."
The New York resident said she was seated near the back of the plane and was asleep when she heard a loud noise.
She said the plane was fairly quiet because everyone was wearing an oxygen mask, while some passengers were in tears and others shouted words of encouragement.
FOX 29 reported that 12 passengers required medical treatment.
News helicopter footage showed damage to the left engine of the plane and the tarmac was covered with foam from fire crews.
Passenger Marty Martinez did 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 "there was blood everywhere" on-board.
"First there was an explosion almost immediately, the oxygen masks came down and within a matter of 10 seconds, the engine then hit a window and busted it wide open," he said.
'BRAVE PILOT' KEPT CALM FOR LANDING
Passengers have praised the "amazing, incredible" pilot Tammie Jo Shults, 56, who bravely flew the doomed plane to safety.
In a message to air traffic control, reports claim she calmly called for assistance.
"We have a part of the plane missing. So we're going to need to slow down a bit ... They said there is a hole and someone went out."
Shults, a New Mexico native and mother-of-two, was one of the first female fighter pilots for the US navy.
She was also the first woman to fly the F/A-18 strike fighter.
She joined Southwest Airlines in 1993. Shults' name has not been officially released by Southwest Airlines, but passengers who were on the flight have revealed via social media that she was the pilot.
On Instagram, @abourman wrote the post above. "Our engine that blew out at 38000 ft. A window blew out, a man saved us all as he jumped to cover the window. … The pilot, Tammy (sic) Jo was so amazing! She landed us safely in Philly."
Diana McBride Self wrote on Facebook: "Tammie Jo Shults, the pilot, came back to speak to each of us personally. This is a true American hero. A huge thank you for her knowledge, guidance and bravery in a traumatic situation. God bless her and all the crew."
CHILLING MAYDAY EMERGENCY CALL
In audio of the air traffic control radio call, which was obtained by NBC Philadelphia, co-pilot Shults can be heard calmly describing the scary situation.
"We have a part of the aircraft missing, so we're going to need to slow down a bit," she can be heard saying.
Ms Shults then asks for medical personnel to meet the plane on the ground to assist with injured passengers.
When asked whether or not the plane was on fire, her response was: "No, it's not on fire but part of it's missing," she says. "They said there is a hole and … and, uh, someone went out."
MOTHER IDENTIFIED AS DEAD PASSENGER
Jennifer Riordan, 43, was the only passenger to have died on the doomed plane, according to her former employer.
In a recording of conversations between the cockpit and air traffic controllers, an unidentified crew member reported that there was a hole in the plane and "someone went out," passenger Alfred Tumlinson, of Corpus Christi, Texas, said.
A man in a cowboy hat rushed forward a few rows to grab the woman and pull her back in.
"She was out of the plane. He couldn't do it by himself, so another gentleman came over and helped to get her back in the plane, and they got her," he said.
Another passenger, Eric Zilbert, an administrator with the California Education Department, said: "From her waist above, she was outside of the plane."
Passengers struggled to somehow plug the hole while giving the badly injured woman CPR.
The mother-of-two, who had been married to her husband Michael for 20 years, reportedly died from her injuries, which are unknown at this stage, according to KOAT Action 7 News.
NM Broadcasters, a New Mexico television and radio broadcasting company, claimed to be Mrs Riordan's former employer in a tweet about her death.
"Our hearts are heavy with the news of the death of Jennifer Riordan today," the tweet read.
Mrs Riordan was most recently the vice president of community relations at a financial services company called Wells Fargo in Albuquerque, while her husband was previously the COO of the City of Albuquerque.
It is understood the long-term couple have two young children, a son and a daughter.
Riordan's Twitter account shows she tweeted on Monday about her stay at a hotel in New York during a 'business' trip.
She described herself in her bio as: "@wellsfargo proud Team Member. Wife, mom of two, baseball fan, wine and coffee lover, passionate about my community."
INVESTIGATION NOW UNDERWAY
The Philadelphia airport tweeted that flight 1380 'landed safely at PHL and passengers are being brought into the terminal.' Flight 1380, a Boeing 737-700, was carrying 144 passengers and five crew members.
Investigators from the National Transportation Safety Board (NTSB) recently arrived in Philadelphia to inspect the plane..
Meanwhile, in a statement, Southwest said it was also investigating the incident.
"We are in the process of gathering more information," the statement said. "Safety is always our top priority at Southwest Airlines and we are working diligently to support our customers and crews at this time."
The plane was powered by CFM56 engines, which are made by CFM International, a joint venture between General Electric and France's Safran.
CFM are the sole supplier of engines for 737-700 planes.
Southwest CEO Gary Kelly addressed the incident in a live conference streamed on ABC 6 shortly afterwards.
"To my knowledge it's the first time we have lost a window," he said.
"It's the first fatality for the airline.
"The engine dates back to 1997 — only a handful of incidents like this that have happened.
"I want to thank and commend our flight crew for their swift action.
"They handled the situation magnificently, the aircraft was at altitude and this was a very serious event and obviously we are very grateful there were no other injuries other than the one fatality.
"Our crew performed magnificently."
The aircraft was delivered in July 2000, and was last inspected on April 15, three days ago. There was no information that there was any problem with the plane or engines as a result of that inspection.
"All our 737s have that engine, we previously had the 737-300 it had a different engine but all of those aircraft have been retired," Mr Kelly said.
The NTSB conducted an investigation of a similar Southwest incident in 2016 involving the same type of engine.
In that incident, a fan blade snapped off a Southwest 737-700 engine mid-flight, sending debris slamming into the plane and damaging the fuselage, wing and tail.
NTSB investigators later found evidence of a crack consistent with metal fatigue on the titanium-alloy blade. However, no one on that flight was hurt.
SHOWER OF SPARKS
Southwest is notable among airlines because the only airplanes it flies are various models of the Boeing 737. The airline started out as Air Southwest in 1967, adopting its current name four years later.
While the airline has established a record of safety, there have been several incidents.
Almost five years ago, a Southwest flight from Nashville, Tennessee, crash-landed at LaGuardia Airport, scraping down the runway in a shower of sparks before ending up just off the runway.
In 2011, a plane bound for Sacramento diverted to Yuma International Airport in Arizona after a portion of the airplane's skin peeled back, causing a gaping hole in the cabin area.
That 2011 incident came two years after a flight headed from Nashville to Baltimore-Washington International Airport had to land in Charleston, West Virginia, after a hole opened near its tail.
A 6-year-old boy who was sitting in a car died in 2005 when a Southwest plane landing in the snow at Chicago's Midway International Airport skidded off the runway and into a street.
Five years before that, a passenger named Jonathan Burton broke down the cockpit door on a flight from Las Vegas to Salt Lake City. Other passengers restrained Burton, who died later from the resulting injuries.
That same year, 2000, a plane landing at the Hollywood Burbank Airport overran the runway, injuring 43 on board. The captain of the flight later was fired.
Additional reporting: Washington Post