By John Crawley

WASHINGTON (Reuters) - Airlines would be requiredto give pilots longer rest periods and scale back duty timeunder a government proposal on Friday aimed at combatingfatigue in the cockpit.

The Federal Aviation Administration (FAA) changes, iffinalized, could force airlines to hire more pilots, changeflight schedules, and revamp negotiated union work rules.

Major carriers are very sensitive to any mandate that wouldraise costs just as their finances are improving following arecession-driven downturn.

Unionized pilots at several carriers have been pushing formore flexible work schedules and more hiring.

Big carriers like Delta Air Lines, UAL Inc'sUnited Airlines and Continental Airlines eachemploy thousands of pilots. The impact of any change woulddepend on a carrier's internal policies on fatigue.

The FAA regulation also would apply to operations at U.S.regional carriers, such as Delta's Comair affiliate andPinnacle Airlines Inc's Colgan Air.

Airlines have warned that if the regulations, which werewidely expected, are too onerous, carriers could wind upreducing capacity to keep costs in line.

The industry's leading trade group, the Air TransportAssociation, said in a statement that it was evaluating the FAAproposal and would support new fatigue standards if they werescientifically based and "crafted to truly improve safety."

MINIMUM REST PERIODS

Under pressure from families of the victims of a Colgancrash last year in New York that killed 49 people and raisedquestions about crew scheduling, Congress required new effortson pilot fatigue and training this summer.

The FAA proposed a nine-hour minimum rest period prior toflying, geared toward ensuring adequate sleep. That would be aone-hour increase over current rules.

To prevent fatigue over weekly and monthly schedules, theFAA proposed new limits on the amount of time a pilot can be onduty. For instance, pilots must receive at least 30 consecutivehours free from duty weekly, a 25 percent increase over currentrules.

The FAA, which accelerated work on the fatigue measureearlier this year under its administrator and former pilot,Randy Babbitt, first proposed updating pilot rest rules in themid-1990s. But regulators never finished the work due toshifting agency priorities, political wrangling and unresolvedtechnical questions on how to proceed.

The Colgan crash, in which a Bombardier DHC-8-400 plungedinto a snow-covered neighborhood as it neared Buffalo, NewYork, on Feb. 12, 2009, exposed serious questions about pilottraining.

The National Transportation Safety Board noted as part ofits investigation that pilots for smaller carriers can commutelengthy distances to work, experience hectic and long days, anduse crew lounges to catch up on their sleep during breaks.

These smaller airlines perform a substantial amount ofshort-haul flying for their big affiliates.

The FAA proposal says it is unreasonable to assume that apilot is resting while commuting, and that airlines would berequired to arrange adequate rest periods outside of commutinghours.

The new rule would give airlines some flexibility onscheduling, considering that airline operations vary, includingaircraft type, routes, and staffing.

The proposal is subject to a 60-day public comment period. (Reporting by John Crawley; Editing by Lisa Von Ahn)