The Federal Aviation Administration has postponed until spring the long-awaited update of its decades-old regulations on managing pilot fatigue, despite pressure from Congress to act sooner.

Ultimately, the proposal will incorporate the latest sleep and fatigue science—including how late-day departures affect pilot performance—and will be broader than originally planned, an FAA spokeswoman said.

In December, an FAA official told a U.S. Senate subcommittee on aviation safety that the agency would not meet its year-end 2009 target but would unveil the proposal in January. This month, however, the spokeswoman confirmed the new target date of late March or April for the revamped pilot fatigue regulations.

Fatigue regulations govern passenger airlines and charter operations, though not identically. They do not apply to general aviation, including corporate fleets. The regulations have been in place with little change since the 1940s, according to the FAA.

In recent years, the National Transportation Safety Board has cited pilot fatigue as a possible factor in several incidents, including the February 2009 fatal crash of a Colgan Air Inc. passenger jet near Buffalo, N.Y. Other incidents involved pilots flying past destinations, dozing and taxiing planes off runways after landing.

But the NTSB since 1989 has urged the FAA to update its fatigue regulations. The FAA floated a couple of proposals since 1995, but it withdrew both last year because of insufficient industry and labor support.

Largely because of the Colgan crash, Congress looked into the issue last year and pressed the FAA to update the regulations.

Meanwhile, aviation insurance underwriters also are paying greater attention to their policyholders' fatigue management protocols, brokers say.

While some airlines' own fatigue management protocols exceed FAA regulations, economic conditions force most airlines to work pilots nearly as hard as the rules permit, said John Prater, president of the Washington-based Air Line Pilots Assn. International and a commercial airline pilot.

The FAA spokeswoman agreed.

The agency's latest delay in revamping the regulations was necessary because of the complexity of integrating the latest scientific findings with the rulemaking consensus reached on many points by various aviation industry representatives, the spokeswoman said. Representatives of management and labor collaborated with the FAA as part of a special rulemaking committee last summer.

While she would not provide details about the forthcoming regulations, the spokeswoman said, “The big thing we're trying to fix is rest time.”

Pilots must have at least eight hours of rest during any 24-hour period involving flight time. Rest begins when a pilot parks a plane at a gate and it can end as soon as eight hours later with the pilot backing another plane away from its gate.

ALPA wants a 10-hour rest period.

The FAA also plans to “fix” a regulation allowing pilots to be “on duty” 16 of every 24 hours. That provision is “unclear” and, because of union contracts, “on duty” means something different to each operator, the spokeswoman said.

The industry mistakenly assumes the proposal will not address pilots' personal commuting time—when pilots travel from their homes to their base airports during off-duty hours at the outset of multiple-day shifts, the spokeswoman said.

Commuting time “will be taken into account,” she said. The proposal might not specifically mention “commuting,” but it is an important element of fatigue management that will be addressed, the spokeswoman said.

Several industry observers, however, said regulating any activity during pilots' private time would be challenging.

Ultimately, a pilot has the responsibility to be rested and refuse to fly when fatigued, said airline consultant and former airline pilot James F. Barnette, an executive partner with transportation energy and environment consulting firm Nexxt Steps L.L.C. in Princeton, N.J.

Once the FAA unveils its proposal, interests that participated in the rulemaking committee might suggest modifications.

For example, the Washington-based Regional Airline Assn. has retained Washington State University's Sleep and Performance Research Center in Spokane to conduct fatigue management research on pilots operating short-haul flights. Preliminary results should be available when the FAA invites comments on its proposal later this year, said RAA President Roger Cohen.

Mr. Cohen said fatigue research is abundant, but little of the research focuses on pilots.

For that reason, he questioned the widely held assumption that multiple takeoffs and landings that a pilot executes during a shift for a short-haul flight is more fatiguing than a single takeoff and landing by a pilot flying a long route. Short-haul flights might be comparable to adrenaline-pumping city driving while a longer route might be similar to a boring daylong drive along a flat Midwestern highway, he said.

William R. Voss, president and CEO of the Alexandria, Va.-based Flight Safety Foundation, agreed that “there's a gap in the science on the number of ups and downs” that fatigue pilots.