First, there was an explosion as the plane's left engine failed. Then shrapnel from the engine shattered a window, causing oxygen masks to be released and forcing the flight, originally bound for Dallas, to make an emergency landing in Philadelphia.
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The woman sitting closest to the blown-out window was nearly sucked out. She died and seven others were injured.
Meantime, the NTSB is taking apart the engine, examining maintenance records, and focusing on a missing fan blade.
"This fan blade was broken right at the hub and our preliminary exam of this was that there is evidence of metal fatigue where the blade separated," said the NTSB's Robert Summwalt.
ABC7 News spoke with ABC Aviation Expert, John Nance. "One of the things they need to look into is who is doing the maintenance and the overhaul in particular on these engines."
VIDEO: Passenger recounts terrifying moment inside plane after emergency landing
The plane was inspected on Sunday. Meantime, passengers at Oakland International Airport, where Southwest is the largest carrier, have mixed reactions to the incident.
"We just flew on a Southwest plane so it was kind of creepy to get on a plane and not know if something similar was going to happen with the plane we were on," said passenger Lisa Friedman.
"I think the chances of the same thing happening on another Southwest flight on the same day are infinitely small," said passenger Jim Corr.
The NTSB's investigation could last 30 days.
Click here for a look at recent stories and videos about emergency landings here in the Bay Area and across the country.