Airlines are finding new ways to operate and maintain planes, but government safety inspectors aren't keeping up with potential new risks those changes create, says a report released Wednesday.

The Federal Aviation Administration (search) "still has a substantial amount of work ahead to improve its oversight systems, especially given the magnitude of changes air carriers are making and the pace at which the changes are occurring," said the report by the Transportation Department's (search) inspector general.

The FAA disagreed with the report's conclusion that the agency hasn't noticed or accounted for changes in the airline industry.

Its oversight system is working well, said FAA spokeswoman Alison Duquette (search). "We're in the safest period in airline history for the past three years," she said.

The report looked at five major airlines that have lost record amounts of money but noted that the FAA only stepped up its surveillance at the three that are in or near bankruptcy. The agency has a policy of increasing inspections of financially troubled airlines.

The report also noted that airlines are turning planes around faster at gates — and sometimes don't follow required operating procedures — but FAA inspectors didn't consider that practice as a potential risk.