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.

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

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.

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