Last month Captain Tammi Jo Schults became an American hero when she successfully landed her Southwest Airlines Boeing 737 after a window shattered. One passenger was killed in the horrific accident.

The National Transportation Safety Board immediately launched an investigation as Southwest grounded all of it’s 737’s for inspection.

On Thursday, the NTSB released an update in their report on the cause of the shattered window. 

A jagged chunk of an engine part called the inboard fan cowl hit a window, shattering it and causing a partial loss of pressure in the cabin that pushed 43-year-old Jennifer Riordan halfway out the window. She died later.

The National Transportation Safety Board provided new details Thursday on the fatal accident aboard Southwest Flight 1380 on April 17.

In its update, the NTSB also said that investigators have found pieces of the broken engine fan blade suspected of triggering the accident when it snapped off due to metal fatigue, or microscopic cracking. The NTSB said the other blades in the engine on the Boeing 737 were nicked during the accident but showed no signs of cracking.

Investigators looked at Southwest maintenance records, which indicated that the fan blades in the failed engine had made more than 32,000 flights and more than 10,000 since being overhauled in November 2012. At that time they were inspected by sight and with fluorescent dye used to find surface defects.

Since the accident, the Federal Aviation Administration has announced stepped-up inspections of fan blades in Boeing 737 engines, which are made by CFM International, a joint venture of General Electric Co. and France’s Safran SA. CFM first recommended more inspections using ultrasound and electrical currents after an engine broke apart on another Southwest plane in 2016. No one was injured in that incident.

 

Southwest has since examined more than 25,000 engine fan blades in their fleet, saying they have so far only found one that displayed metal fatigue.