FAA has proposed a $4 million civil penalty against United Parcel Service (UPS) for allegedly failing to follow FAA-approved procedures for making structural repairs to two DC-8 freighter aircraft and two MD-11Fs.

The agency said the company’s Louisville, Ky.-based UPS Airlines unit operated the four aircraft on more than 400 flights between October 2008 and June 2009 “when they were not in compliance” with federal aviation regulations. UPS called the proposed penalty “unwarranted.”

FAA said in a statement, “These violations stem from UPS’s failure to fully comply with the terms of a consent agreement in which the carrier agreed to inspect all aircraft in its fleet and compare actual repairs with maintenance records. This would have ensured the four aircraft were in compliance with the regulations.”

In an emailed statement to ATW, UPS Airlines spokesman Mike Mangeot said, “UPS has a long history of operating a safe, compliant airline. The proposed FAA penalty related to the documentation of nine repairs on four aircraft is unwarranted and unreasonable. There was never a safety issue. We believe we were compliant with FAA rules and will vigorously defend our position.”

UPS has 30 days to respond to the agency.