Beginning in 2006, the Dallas-based airline conducted "extreme makeover" alterations to eliminate potential cracking of the aluminum skin on 44 jetliners, the FAA said. An FAA investigation found that both the airline and its contractor, Aviation Technical Services, Inc, of Everett, Washington, failed to follow procedures for replacing the fuselage as well as other work on the planes. Southwest then returned the jets to service in 2009, the FAA said, despite being warned that the aircraft were not in compliance.
The FAA later approved the repairs after the airline provided documentation that the repairs met safety standards. "Safety is our top priority, and that means holding airlines responsible for the repairs their contractors undertake," said U.S. Transportation Secretary Anthony Foxx in a statement.
Southwest has 30 days to respond. "Having fully resolved the repair issues some time ago, none of the items raised in the FAA letter affect aircraft currently being operated by Southwest Airlines," a Southwest spokeswoman told NBC News. "Safety is paramount and we always strive for full compliance with established and approved processes and procedures."