Story highlights FAA proposes $354,500 fine for US Airways

Officials say airline flew jet 916 times without required tests

US Airways spokeswoman says flights were "in compliance"

Federal officials have proposed penalizing US Airways $354,500 because, they say, the airline flew a jet 916 times after failing to perform required tests and an inspection on an engine repair.

In a letter to the airline dated August 3 but disclosed Wednesday, the FAA said the airline performed maintenance on a Boeing 757-2S7 on August 3, 2010. After discovering a leaking fuel pump in the right engine, the airline replaced the pump but failed to perform two mandatory tests and a required inspection.

As a result, US Airways returned the aircraft to service in a condition the FAA deems unairworthy, the letter says.

A US Airways spokeswoman said, "We are in the process of responding to the FAA and believe the flights were flown in compliance with applicable rules."

By law, the airlines has 30 days to respond to the FAA.

The airliner was an ETOPS, or extended operations, plane: one certified to fly long distances on routes that previously were off-limits to single-engine or twin-engine aircraft.