The Federal Aviation Administration issued the fine Thursday after the airline continued to fly more than three dozen jets beyond the date inspections were due. When they were finally inspected, six planes had cracks, one with a crack in the fuselage measuring 4 inches across, The Dallas Morning News reported.
"That decision (to delay inspections) could have jeopardized people's lives," an industry analyst said.
However, Southwest pointed out that it voluntarily pointed out the problem to FAA officials in March 2007.
Critics also suggested that the FAA's partnership program in which airlines cover some safety issues themselves, is flawed.
"We are depending way too much on the airlines and there are not enough checks and balances in place," said Linda Goodrich, regional vice president for an FAA inspectors' union.
Some questioned why the FAA didn't simply ground the jets when the issue was first reported, the newspaper said. But, the FAA said the official who permitted flights to continue was removed from the job, said FAA spokeswoman Laura Brown.