Atlas Airlines intends to "vigorously defend itself" against a proposed $275,000 civil penalty by the US Federal Aviation Administration (FAA) which alleges that the US freighter lessor operated a B747 after performing what the agency describes as “improper maintenance” on the aircraft nearly five years ago.

In a statement, the US aviation regulator said: "The FAA alleges that Atlas maintenance workers improperly repaired the plane’s landing gear after it would not retract on departure from Sydney, Australia. Atlas repaired the gear using the wrong part, and maintenance workers had to install the component upside down to get it to fit, the FAA alleges.

"Atlas operated the aircraft on 24 cargo flights over a 10-day period after improperly repairing the landing gear, the FAA alleges. The aircraft was not in an airworthy condition during those flights, the agency alleges."

A spokesperson for Atlas said: "We have reviewed the FAA's allegations in this case, which stem from an event that occurred and was addressed nearly five years ago. Atlas intends to vigorously defend itself.

"To that end, Atlas has requested an informal conference with the FAA and we look forward to resolving this matter with it. Our record clearly demonstrates we are committed to the highest levels of aircraft maintenance and safety. We take our responsibility to operate aircraft very seriously."

Atlas has had a busy first quarter to the year. In February, it confirmed that it had enjoyed “solid peak-season volumes and yields” in the fourth quarter of 2015, although it reported a net income loss of $37.5m due to a litigation settlement. And, in January, Atlas announced that it had entered into a “definitive agreement” to acquire Southern Air Holdings for a fee of $110m.