>> number one engine failure boeing 737, 149 souls on board. >> reporter: once on ground, investigators found a fan blade inside the left engine had broken apart in flight, tearing off a piece of the engine cowling, or casing, that shattered jennifer riordan's passenger window she left behind two children and her husband michael. >> she was genuine and pure to her core. >> reporter: it was the second fan blade to break off a southwest 737 in less than a year. investigators determined a metal fatigue crack had gone undetected for years southwest immediately inspected all of its similar fan blades and found 16 additional cracks today the ntsb called on boeing and engine maker cfm to make design changes and protect planes from similar failures >> we are to take something very tragic and try to learn from have to got others don' through this. >> reporter: boeing says it's working on a that would fully address the safety recommendation from the ntsb