Although America West and US Airways combined four years ago, the "new" airline still feels scattered turbulence stemming from the merger.

The latest evidence came Wednesday, when the Federal Aviation Administration announced a proposed $5.4 million fine for US Airways for a series of maintenance violations over a nine-month period that ended in January.

It is one of the largest proposed penalties of its kind against a major airline. But the proposed fine is much less than the record $10.2 million proposed against Southwest Airlines last year for maintenance lapses.

The FAA's allegations center on missed inspections, some dictated by the FAA, others by the airline's maintenance program.

There are no allegations that the airline was ignoring needed repairs for its fleet of more than 600 planes or putting passengers in danger with its missteps.

The agency says US Airways flew nearly 1,700 flights on eight planes that were not in compliance. The time period was May 2008 through January.

In one case, the FAA said, the carrier flew 855 flights on an Airbus A320 that was not in compliance with the airline's engine-repair maintenance requirements. Fifty-one of those flights were flown after the FAA notified the airline in December that it was not in compliance.

US Airways Chief Operating Officer Robert Isom said that the lapses were largely due to inspections overlooked during the combination of the two airlines' computerized maintenance-records systems. That did not occur, he said, until 2008, a year after it received a joint operating certificate from the FAA.

"As maintenance programs were revised and rewritten and those were put into computer tracking systems, there was some fallout," he said.

The airline also ran into major flight problems when it combined its computer-reservation systems, and it is still trying to integrate its flight crews.

Isom said that the airline reported some of the maintenance issues to the FAA and that the agency brought others to its attention.

As a result of the series of maintenance deficiencies discovered, the FAA late last year decided to do a comprehensive review of US Airways' maintenance programs, policies and personnel, Isom said.

"The FAA sat down with us and said, 'Hey, you really need to address these, and you need to address them quickly and comprehensively,' " Isom said.

He said the airline was not forced to ground planes en masse to address the problems.

The review was completed in August.

"This is something that we've known about for a while . . . and, really, closed out most everything to the FAA's satisfaction a couple months ago," he said.

Bill Waldock, professor of safety science at Embry-Riddle Aeronautical University in Prescott, said the FAA's findings against US Airways appear to be mostly paperwork errors, rather than poor-maintenance procedures.

"I'm not minimizing it or saying it isn't important, but it doesn't rise to the level where it is an obvious (flight) hazard that's been ignored," he said.

He said anytime you merge two airline-safety programs with countless details about each plane in the fleet, "you're going to find things fall through the cracks." Waldock said the FAA's decision to do a comprehensive review of US Airways' maintenance programs shows the "system is working."

Waldock found the agency's allegations and a $3.8 million proposed fine against United Airlines, also announced Wednesday, more significant.

The FAA says United flew one Boeing 737 on more than 200 flights when it was not in an "airworthy condition."

The agency said the Chicago-based airline did not follow its own maintenance procedures in December 2007 when towels instead of protective caps were used to cover openings in the "oil sump" area of the engine. The plane had to return to Denver after shutting down an engine because of low oil-pressure indications, the FAA said. "I think the FAA was a little bit more concerned about something like that," Waldock said.

Isom said US Airways expected a fine for the violations but would not say whether it expected the proposed amount to be as high as $5.4 million.

The airline has not disputed any of the findings and has cooperated fully with the FAA, he said. US Airways has 30 days to respond to the agency.

In determining proposed fines, the FAA has a formula that includes the number and type of violations and how many flights were involved during the period when the airline was not in compliance. In some cases, such as US Airways', the proposed fine covers multiple issues; in others, such as the United case, the fine covers a single matter. That makes it difficult to compare the size of fines.

Airlines often negotiate a lower settlement. Southwest, which was accused of maintenance lapses on the fuselage, settled earlier this year for $7.5 million.