Southwest Airlines said it is ready for a fight with federal regulators over a possible $10 million fine.

The Federal Aviation Administration said it is planning to seek the penalty against the airline for failing to inspect older planes for cracks.

Southwest is one of the main carriers at New Hampshire's Manchester-Boston Regional Airport.

The FAA said Southwest did not inspect older planes for cracks and then flew them before inspections were done.

The FAA said Southwest operated nearly 60,000 flights in 2006 and 2007 using 46 planes that had missed inspections for possible fatigue-related cracking.

And the government said the airline flew another 1,451 flights with the same planes last March, after discovering that it had failed to conduct the required inspections.

Southwest said six of the planes had small cracks that required repairs.