Nightly News   |  April 03, 2011

How common is metal fatigue?

Lester Holt asks talks to former NTSB investigator Greg Feith about the Southwest Air emergency landing on Friday.

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This content comes from Closed Captioning that was broadcast along with this program.

>>> join us. it had a maintenance check in march last year, a bit over a year ago come these new cracks have developed over a 12-month period or were they in a place that perhaps no one was work?

>> a combination of both, lester, because where these cracks have form ready in what they call the lap joint and they are subsurface, they are microscopic, if you will. they can't be seen by a visual inspection . even though he there are a number of required inspections in that particular area. so the only way you are going to find these cracks is through ndt or nondestructive testing methods like eddy current or some of the other methods, x-ray, and that kind can of thing.

>> let me ask you this, this 300 model of the 737 is out of production. they make a whole new generation of the airplane, the 7, 8, 900s. are these at risk of having the same kind of 00 issue?

>> not really because they are a newer generation of airplane and the lessons learned from these previous versions have gone into the structural design changes for the later generation airplanes. so you're going to see it just confined to 737- 300 series .

>> important inform information folks flying. thank you, greg fife, we appreciate it.