Old-line carriers such as Delta, American, United, Continental and Northwest were pushed to the brink of extinction in the first half of this decade by recession, Sept. 11 and smaller, more nimble competitors.

Now, after years of restructuring - sometimes in bankruptcy court - they are armed with reduced costs, overhauled routes and fleets that allow them to attract a greater share of high-paying business travelers.

The results also show why a reinvigorated Delta is a tempting takeover target for US Airways, which launched a hostile bid last week for the carrier that operates a hub in Salt Lake City and employs 3,900 Utahns.

All the major legacy airlines turned third-quarter profits, while discounters AirTran and JetBlue were in the red and Southwest and Frontier posted sharply lower profits - a stark reversal of fortune for both groups. Whether the turnabout was a fluke remains to be seen, but some experts think the legacy carriers are back to stay, even though labor challenges loom.

"The network carriers have got their costs down, but that's only part of the story," said Michael Boyd, a Colorado-based airline consultant. "They've also got the Shreveport-to-Shanghai advantage. That's the ability to take people, especially businesspeople, to large and small commercial centers all over the world.

"It's allowing them to grow their revenue at a far faster rate than low-cost carriers. Wall Street and the academics have been so focused on airline costs, they haven't been paying attention to the revenue side of the ledger."

AirTran, Frontier, JetBlue and Southwest have long derived benefits from their simple fleets with few aircraft types - a strategy that cuts maintenance and training costs. But Boyd says they share a disadvantage, too. Their one-size-fits-all fleets are too big for some small markets, and too small for distant, international ones.

Only legacy carriers can efficiently make the connections between such large and small, near and distant locations.

"Hub-and-spoke systems may not seem efficient to travelers going through them," said Ray Neidl, airline analyst at Calyon Securities. "But they offer a lot more flights to a lot more small and midsized cities, and frequent flights are critical to the business travelers who pay premium fares."

Neidl said legacy airlines will never beat smaller, younger, point-to-point carriers on costs. But he said legacy carriers have become so lean that their costs are "within striking distance," and they offer first-class upgrades and other amenities that low-cost competitors can't match.

Increasing revenue can be difficult for carriers that define themselves by low prices, Neidl said, especially during periods of rising oil prices, when larger carriers usually join each other in raising fares.

American, Continental, Delta, Northwest and United have raised ticket prices 22 times in the past two years, regained market share and returned to narrow profits after five disastrous years of multibillion-dollar losses. Now they are recalling some workers after tens of thousands of layoffs. Delta plans to bring back 1,000 furloughed flight attendants next year.

The legacy carriers' near-death experience has forced them to radically reduce their cost structures, with Delta, Northwest and United canceling or paring back employee pensions and benefits, and lowering debt in bankruptcy court. Neidl expects the industry to earn $5.6 billion next year, its first profitable year since the terrorist attacks of 2001.

Boyd said he has stopped using the term "legacy" to describe the network carriers because in fact they are among the most dynamic companies in their industry. He also says the term "low cost" is becoming a misnomer, particularly at Southwest, where pay rates are among the industry's highest.

FLTops.com, an Atlanta firm that tracks airline industry trends, shows the pay gap between legacy and low-cost airlines has narrowed and, in a few cases, completely turned around.

A 12-year Boeing 737 captain at Delta makes $149 an hour. That's about $4 an hour less than an AirTran pilot with the same experience flying the same kind of plane.

Low-cost carriers used to be able to cherry-pick new routes and compete exclusively against legacy airlines. Now, after years of expansions, low-cost carriers are increasingly bumping up against each other.

Southwest began flying to Denver International Airport this year, even though the facility is a United hub also served by low-cost Frontier. Hubs with dominant carriers and high traffic levels are exactly the kinds of places Southwest has studiously avoided throughout its history.

Other low-cost carriers such as AirTran and JetBlue have scaled back growth plans and delayed new aircraft deliveries.

AirTran officials say resurgent legacy carriers are taking advantage of U.S. bankruptcy laws they call unfair and immoral. They say the legacy airlines' strong third quarter was an aberration.

"They may have some short-term success cutting costs in Chapter 11," said Stan Gadek, AirTran's chief financial officer. "But their costs will never be lower than the day they exit bankruptcy."

Jim Parker, airline analyst at Raymond James, is predicting newly profitable legacy airlines soon will face unending demands from resurgent labor unions. Workers made deep concessions to keep legacy airlines flying, and Parker says they are sure to insist on major wage and benefit gains, as happened last week when USAirways' pilots picketed at several airports to protest the slow pace of contract talks.