By ANDY PASZTOR

Representatives of the airline industry and pilots unions agreed to an overhaul of rules aimed at combating cockpit fatigue, according to people familiar with the situation, a move that could bring sweeping changes to the way airlines run their operations.

The group urged Federal Aviation Administration chief Randy Babbitt on Wednesday to jettison decades-old regulations that set uniform limits on how many hours pilots can fly and replace them with more flexible rules based on scientific studies about what causes fatigue. The recommendations call for drafting rules that would limit each pilot's flight hours based on the time of day, the number of takeoffs, or segments, during a trip, and the internal body clocks of pilots.

The proposal envisions a sliding scale of between seven and 11 scheduled flight hours for pilots per day, compared with the current maximum of eight hours, these people said. Rules on total hours spent on duty, which aren't regulated as strictly as flight time, also would be adjusted.

If the FAA moves to implement such far-reaching changes -- which could come at the earliest by the end of next year -- it would substantially alter the workdays of many pilots. It would also likely increase personnel costs for many regional carriers, which fly shorter routes. Many commuter pilots -- who work grueling schedules that include multiple takeoffs and landings a day -- likely would have less time behind the controls than they do now.

But major carriers could save, for example, because they could schedule the same cockpit crew for a morning trip from the West Coast to the East Coast and then a return flight the same day, according to people familiar with the proposal. Rules now require a new crew on the second flight.

Mr. Babbitt has championed efforts for change in the wake of recent airliner incidents and accidents, including February's crash of a Colgan Air turboprop near Buffalo, N.Y., that killed 50 people. That accident highlighted widespread fatigue faced by commuter crews stemming from reduced rest periods and workdays lasting up to 16 hours.

Although the U.K. and other countries pioneered scientifically based pilot scheduling years ago, the U.S. has largely stuck with a one-size-fits-all rule because regulators, airlines and pilots couldn't agree on changes. But in recent years, lawmakers, federal air-accident investigators and outside safety experts have intensified their calls for a sweeping rewrite of fatigue regulations.

In spite of broad agreement on much of the package, some portions remain controversial, and the FAA ultimately will have to sort out disagreements. Some of the thorniest disputes involve cargo airlines, which contend they would be economically devastated by portions of the proposal. Some charter carriers that routinely fly at odd hours complain they would also be handicapped. These groups are pushing for a separate set of rules, according to people familiar with the talks.

Spokeswomen for the FAA and the Air Line Pilots Association declined to comment, as did a spokesman for the Air Transport Association, which represents mainline carriers. Without discussing specifics, Roger Cohen, head of the country's largest regional airline association, said his group has "total and complete commitment" to the process, and a number of regional airline chiefs participated actively in the deliberations.

Commuter pilots are bound to feel more tired than long-haul crews, according to Mr. Babbitt. "There's weight given to [the number of] takeoffs and landings," Mr. Babbitt said in an interview earlier this year, but scheduling issues "are so intertwined" that "we're obliged to address them all at once."

The same day, the FAA chief told a pilot safety conference in Washington that existing regulations "don't reflect the difference" between commuter and long-haul operations. "Not only does one size not fit all" carriers, he said, "it's absolutely unsafe to think that it can."

Even before discussion of revamped rules, large and smaller airlines stepped up efforts to develop their own fatigue-mitigation techniques and train pilots how to recognize the danger signs of sleeplessness.

Regional carriers have assumed a larger role in domestic aviation by offering their big-airline partners less costly flight crews and high productivity. New fatigue rules could erode some of those advantages because they would be required to use more pilots to cover the same flight hours. As it is, the major airlines, themselves financially strapped, are attempting to cut the rates they pay their regional partners and reduce the number of regional planes under their contracts. So tougher fatigue-mitigation regulations could end up hurting the bottom lines of regional carriers.

One highly-charged area the group of fatigue experts stayed away from involves personal commuting by airline pilots to get to work. FAA and pilot union officials have said individual aviators ought to be held accountable for reporting rested and in condition to start flying. The FAA-chartered group of experts didn't end up making any formal recommendations on this topic, according to people close to the discussions

As federal officials struggle to draft new scheduling principles -- a process a former FAA administrator once called "the third rail of aviation safety regulation" --- European regulators also are working on comprehensive revisions to fatigue-prevention measures. At the same time, international aviation safety groups are prodding other countries and carriers to update workday limits based on the latest scientific data.

—Susan Carey contributed to this article.

Write to Andy Pasztor at [email protected]