The discount carrier, which flew more passengers in the United States than any other airline, flew at least 117 planes in violation of mandatory safety checks, CNN reported, citing documents submitted by FAA inspectors to congressional investigators.

In some cases, the documents say, the planes flew for 30 months after government inspection deadlines lapsed. The report said the planes were "not airworthy."

U.S. Rep. James Oberstar, D-Minn., calling it "one of the worst safety violations" he has ever seen, was expected to seek a hearing on the matter.

Southwest had no comment, CNN said.