The U.S. Federal Aviation Administration today proposed a $325,000 fine against Southwest Airlines for the alleged improper installation of a switch that tests an aircraft’s windshield heating system.

The contested switch was installed on an AirTrain Airways Boeing 717 jet in August 2011 and was present on 1,140 flights before the problem was corrected, the FAA says.

The switch is designed to indicate if the windshield heater on the left, right, or center windshield failed when a warning sounded. In this case, the left and center signals were reversed, the FAA says.

Southwest now has 30 days to respond to the FAA’s proposal.