WASHINGTON — The Federal Aviation Administration on Monday proposed a $12 million civil fine against Southwest Airlines for failing to comply with safety regulations related to repairs on Boeing 737s — the second-largest airline fine it has ever proposed.
The FAA said that beginning in 2006 Southwest made ‘‘extreme makeover’’ alterations to eliminate potential cracking of the aluminum skin on 44 jetliners, and that the contractor, Aviation Technical Services Inc., failed to follow proper procedures. All work was done under Southwest’s supervision, the FAA said.
Southwest returned the planes to service in 2009 even after the FAA ‘‘put the airline on notice that these aircraft were not in compliance’’ with safety regulations.
One finding was that Aviation Technical applied sealant beneath new skin panels but did not install fasteners in all of the rivet holes fast enough for the sealant to be effective, which could lead to gaps that cause corrosion. The FAA also said Southwest failed to properly install a ground wire on water drain masts on two 737s in response to a safety order aimed at preventing lightning strikes.
Southwest has 30 days to respond to the proposed fine. Usually FAA officials negotiate in cases of large fines.
‘‘None of the items raised in the FAA letter affect aircraft currently being operated,” Southwest said.