The Federal Aviation Administration (FAA) announced this week that it has proposed a $325,000 fine against Southwest (LUV -7.17%) as a result of the airline allegedly operating an aircraft that violated federal regulations through improper modifications.

According to the FAA, in August 2011, maintenance crews at AirTran Airways (which Southwest acquired in May of 2011) didn't correctly install a switch used by flight crews to test if the windshield heating system on a Boeing 717 was operating correctly. Before the problem was recognized and corrected, the aircraft made more than 1,100 flights.

As a result of the improper installation, the testing system reversed the information given to maintenance crews surrounding whether or not the windshield heating system was working properly on two of the windshields, according to the FAA. Although the right windshield operated correctly, the left and center warning indicators were reversed. According to the FAA, "proper installation of the switch would have allowed personnel to isolate the windshield anti-ice system that was causing a warning that the windshield heater was failing."

Southwest said in a statement on the proposed fine that the problem was immediately fixed after its discovery, and that it did not result in "a Safety of flight issue as the primary notification system remained effective to alert the Crew of a potential window heater malfunction." In addition, the modification was an additional feature made available, the airline said, and it was added after the delivery of the aircraft as an enhancement.

"We were aware of the proposed penalty and have been actively working with the FAA on a resolution," noted the company in its statement. "Safety is the top priority at Southwest Airlines."

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