Sturgell has acknowledged that the FAA should have grounded the jets last year, when Southwest itself reported that it had inadvertently missed inspections of the fuselages on its all-Boeing fleet. He has said that "at least one FAA inspector looked the other way."

Rep. James Oberstar, D-Minn., chairman of a House committee looking into the actions of both the airline and the FAA, said this week's groundings and fresh inspections raised serious questions about the FAA's follow-up to the missed examinations last year.

Beyond Wednesday's canceled flights — airline officials said they expected to operate a normal schedule on Thursday — it was unclear what impact the unfolding events might have on Southwest's ticket sales and reputation.

Ted Marzilli, an executive at consumer-surveying firm BrandIndex, said Southwest's ratings have held up, despite nearly a week's worth of bad publicity. But Wednesday's news of airplanes being grounded and flights canceled could change things for the worse, he said.

The $10.2 million penalty is the largest the FAA has ever imposed on a carrier. Most of the amount was related to charges that Southwest for several days last year continued to put passengers on planes that it knew had not been properly inspected.

Southwest has said it will appeal. CEO Kelly, who earlier announced an internal investigation into the missed inspections, said Wednesday that Southwest has a clean record over its 37-year history.

"We have been a safe company. I believe we are a safe company," he said. "I am committed to making sure we become safer still."

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Contributing: Brice Wallace, Deseret Morning News.