Southwest Airlines Co. said it would challenge a $10.2 million fine levied for flying aircraft that had not been inspected for structural problems, according to United Press International.

The company defended its safety and maintenance procedures Thursday after the Federal Aviation Administration announced the fine against the Dallas-based carrier.

According to the federal agency, SWA flew 42 planes that had missed FAA inspections. The FAA said it was levying the fines over that issue and because six of the SWA planes had some fatigue cracking.

Southwest said in a statement Thursday that there was never safety problem and the oversight was rectified.

"The FAA penalty is related to one of many routine and redundant inspections on our aircraft fleet involving an extremely small area in one of the many overlapping inspections. These inspections were designed to detect early signs of skin cracking," said Southwest's statement.

"Southwest Airlines discovered the missed inspection area, disclosed it to the FAA, and promptly reinspected all potentially affected aircraft in March 2007. The FAA approved our actions and considered the matter closed as of April 2007," the statement said.

The airline also said it worked with Boeing Co., which built its fleet of 737 aircraft. None of the airplanes in question was involved in accidents or other incidents.