"We remain completely confident in the airworthiness of our fleet," she said.

The new FAA requirements stem from a 2009 incident in which a Southwest flight from Nashville to Baltimore had to make an emergency landing in Charleston, W.Va., after a hole more than a foot long appeared in the roof near the tail. Boeing issued a special service bulletin to airlines operating the planes in 2010.

In 2011, a different Southwest jet was forced to land in Yuma, Ariz., but authorities believe that incident involved cracking in a different type of joint where panels of aluminum skin overlap.

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