An engine on the plane blew apart Tuesday, showering the aircraft with debris and shattering a window. Part of a fan blade had separated from the engine, and inspectors found evidence of a crack in the fan blade, which they said was consistent with metal fatigue.
Metal fatigue is a weakening of metal from repeated use and involves microscopic cracks.
The board said it will more closely examine the fan blades and look for engine parts that fell away after the blast as part of efforts to determine the cause. A piece of shrapnel from the blast broke one of the plane's windows, depressurizing the cabin and causing a woman to be partially sucked out of the plane. She also walked through the aisle and talked with passengers to ensure they were OK after the aircraft touched down. Seven other passengers were injured.
Landing the plane, she said: "Thank you, we are going to stop right here by the fire trucks".
Passenger Bobby Martinez shared a photo of the incident on Facebook, showing the oxygen masks hanging from the plane's ceiling and several people wearing them. "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".
Peggy Phillips spoke to WFAA-TV upon her arrival in Dallas Tuesday night. They will only work for a short time, during the time that the pilot gets the plane to a lower altitude where the masks are no longer needed. Then she heard commotion a few rows behind her.
Philadelphia Fire Commissioner Adam Thiel said earlier that one of the 149 passengers and crew members on board was taken to the hospital in critical condition. FAA issued a certificate of registration in 2000 to the Southwest 737 that experienced the latest inflight engine failure.
"All I could think of in that moment was, I need to communicate with my loved ones", passenger Marty Martinez told ABC's "Good Morning America" on Wednesday.
"Engine failures like this should not occur", Robert Sumwalt, chairman of the NTSB, said Wednesday.
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The 56-year-old was in the cockpit of the Southwest Airlines jet when the engine blew up during the journey from NY to Dallas.
One passenger on that harrowing flights said she had "nerves of steel". Shults calmly radioed air traffic controllers in Philadelphia to discuss her approach. She would reach out to you and you were immediately a friend and glad to know her - very, very grounded and positive.
"I've always said, you give me a good person, I can make a good firefighter out of him".
The CFM56 is arguably one of the safest and most popular jet engines in the world, with more than 30,000 units produced since 1980, and it's used on both civilian and military aircraft. Almost 6,700 aircraft around the world are powered by the engines, which have been in use since 1997.
Southwest flies more than 700 737's with an average age of just under 11 years, but it is not uncommon for airliners to fly for 20 years or more. The plane landed safely.
"There needs to be proper inspection mechanisms in place to check for this before there's a catastrophic event", said Sumwalt.
As a result of the 2016 incident, engine manufacturer CFM International, a GE Aviation/Safran Aircraft Engines joint venture, had issued guidance as recently as June 2017 providing instructions for ultrasonic inspection of certain high-time fan blades in the engine type, which powers 737NGs.
As the recent engine failure on Southwest Airlines flight 1380 has shown, it's still possible for something to go wrong.