WASHINGTON (CBS) — The National Transportation Safety Board met in Washington on Tuesday to determine the probable cause of a deadly engine failure on a Southwest Airlines flight. That plane made an emergency landing in Philadelphia.

The engine blew apart on April 17, 2018 and shattered a window.

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Jennifer Riordan, 43, was blown partly out of that window and died of her injuries. Eight other passengers were injured.

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LEFT: CREDIT: Marty Martinez

The NTSB says its preliminary findings point to a broken fan blade in the engine, which caused it to break apart.

The NTSB says the crack was present six years before the accident but went undetected by visual inspections.

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The accident led to more intensive inspections of fan blades on that type of engine. At least 15 other cracked blades were discovered.