WASHINGTON  The Federal Aviation Administration on Thursday issued a $10.2 million fine — the largest in its history — against Southwest Airlines. The FAA said it will seek the fine from Southwest for flying 46 jets during nine months in 2006 and 2007 without performing required inspections for cracks in the fuselage. Cracks eventually were found on six of the planes. The Boeing 737 jets made 59,791 flights before the airline realized in March 2007 that the inspections had not been completed. The airline deliberately made 1,451 more flights after discovering the lapse, the FAA said. The agency transferred an FAA supervisor who had been overseeing Southwest to another job and has "taken appropriate action" against an unnamed employee, spokeswoman Laura Brown said. The inspections were ordered after undetected cracks in an Aloha Airlines 737 allowed a portion of the skin to peel away in flight in 1988, killing a flight attendant. Southwest, the low-fare carrier that now has more domestic flights than any other airline, said it had disclosed the missed inspections to the FAA in March 2007. "We believed at that point that the matter was closed," spokeswoman Linda Rutherford said. Southwest said in a statement that safety was never compromised. The fine comes as the FAA faces a whistle-blower investigation into whether the agency has become too cozy with the airlines it oversees. The allegations stem from an FAA program that encourages airlines to disclose safety problems without fear of being punished. Linda Goodrich, vice president of the Professional Airways Systems Specialists, the union that represents FAA inspectors, said many union members have come forward to complain that the agency abuses the program. "The agency has allowed (airlines) to use this system to get around enforcement actions," Goodrich said. Airlines have been allowed to "disclose" safety problems and escape fines even though inspectors initially discovered the problems, Goodrich said. FAA documents prohibit that practice. The FAA's Brown said she did not know enough about Goodrich's allegations to comment. Whistle-blowers working with the House Transportation Committee had produced "detailed documentation" about the problem at Southwest, said a letter from the Inspector General for the Department of Transportation. Committee Chairman Jim Oberstar, D-Minn., asked the agency to investigate the claims, said the Feb. 11 letter. The committee had planned to hold a hearing on the issue next week, but the hearing was canceled because Oberstar requires hip replacement surgery. The previous high FAA fine was levied last year against TAG Aviation. That fine, $10 million, was for operating charter flights in violation of federal law. Airlines often pay less than the amount the FAA initially seeks. Conversation guidelines: USA TODAY welcomes your thoughts, stories and information related to this article. Please stay on topic and be respectful of others. Keep the conversation appropriate for interested readers across the map.