NEW YORK (CNN) -- The CEO of Southwest Airlines said Friday he has ordered an investigation into charges the discount carrier flew airplanes that weren't properly inspected for safety.



Southwest Airlines CEO Gary Kelly tells CNN the airline is surprised at FAA charges.



Gary Kelly said Southwest was caught off guard when the Federal Aviation Administration notified it on Thursday that it may be hit with a record $10.2 million federal fine for alleged violations involving fuselage crack inspections. Kelly called the fine "unfair" and "unprecedented."



The FAA on Thursday accused Southwest of operating the 47 airplanes last year without conducting mandatory checks for fuselage cracking. The airline has 30 days to respond.



Kelly told CNN safety was never an issue.



"In this particular situation, we identified a gap in our documentation. We voluntarily reported that to the FAA. We worked out with the FAA how to fix that problem, and we fixed it," he said on CNN's "American Morning."



Asked why, then, the discount carrier was called on the carpet, Kelly replied, "We were surprised yesterday to get that notification by the FAA as well. The Wall Street Journal yesterday reported as late as last month the FAA said that it had no safety issues with Southwest Airlines."



"I've ordered an investigation as to exactly what happened in this event," Kelly said. "It occurred in March of 2007. These aircraft are inspected inch by inch. In this particular incident, over 99 percent of the inspections were completed, according to documentation."  Watch what's raising concerns about Southwest »



He said that after fuselage cracks were discovered in about half a dozen of the airline's 737s, 47 planes were reinspected over a 10-day period.



Boeing Inc., the plane's manufacturer, which was contacted when the problems arose, said that at no time were the cracks unsafe, Kelly said. "Cracks do occur. That's why we do inspections."



He said Boeing issued a release Thursday saying Southwest "acted responsibly, and at no time were the aircraft operated in an unsafe manner."



The FAA issued a statement saying that Southwest improperly inspected the planes for cracks, then allowed them to fly an additional 1,451 flights, knowing they weren't airworthy.



Kelly was asked about FAA allegations that an inspector knew about the problems, but continued to allow the planes to be flown. He didn't answer the question directly, saying the airline has an ongoing relationship with the federal agency and there is a complicated system of inspections.



"Our interpretation of the guidance that we got from the FAA at the time was that we were in compliance with all laws and regulations," Kelly said.



"I think the FAA has a different view of that today, and that's something that we're investigating as well. But the important point is that at no time were we operating in an unsafe manner, and I think our history proves it."



Calling the situation detailed in the FAA documents "one of the worst safety violations" he has ever seen, Rep. James Oberstar, D-Minnesota, is expected to convene a hearing to ask why the airline may have allegedly put its passengers in danger. He heads the House Transportation and Infrastructure Committee.  Watch passengers react to the charges »



The FAA documents allege that Southwest flew at least 117 of its planes in violation of mandatory safety checks. The 117 number includes the 47 planes alleged to have flown without fuselage checks and 70 additional planes allegedly flown without mandatory rudder inspections.



In some cases, the documents say, the planes flew for 30 months past government inspection deadlines. It should have grounded them until the inspections could be completed.



The planes were "not airworthy" according to congressional air safety investigators.



Southwest Airlines, which carried more passengers in the United States than any other airline last year, said in a written statement Thursday that it looks forward to making details of the case public -- saying those details will support the airline's actions.



The documents were prepared by two FAA safety inspectors who have
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