Many of the older planes are also gas guzzlers, making them even more expensive to operate as fuel prices hit record highs.
"As planes get older, they just have more and more intense inspections," said David G. Neeleman, the founder of JetBlue Airways, a carrier he started with new planes to keep operating costs low. "All those landings take a toll."
The problem that led American Airlines to ground its fleet of 300 MD-80s this week and cancel more than 3,000 flights was a mundane service issue: how to wrap and attach wiring bundles inside wheel wells. Had American done the work correctly the first time, the turmoil would have been avoided.
But it points to a bigger problem. That fleet, with jets averaging 18 years in age, is subject to hundreds of Federal Aviation Administration airworthiness directives, so maintaining the planes is expensive and a logistical and paperwork nightmare.
Some newer planes, by comparison, are covered by just a handful of directives, making it much simpler and cheaper to keep them in compliance.
The FAA crackdown, along with calls for an overhaul of the agency, threatens to increase maintenance expenses just as the industry is entering yet another financial downturn.
On Friday, Frontier Airlines of Denver became the latest carrier to file for bankruptcy protection, the victim of fuel prices and jittery financial markets.
Fuel costs and an inability to raise fares much have sent most of the industry back into the red after a brief two-year period of profits. For the nine months ended December 31, for instance, Frontier managed to raise its average fare just 21 cents over the prior period, to $102.97.
Now losses for the industry are expected in 2008, and there could be more bankruptcies.
Frontier, with 6,000 employees and 62 Airbus jets, plans to keep flying its normal schedule. But it has struggled to stay aloft in recent weeks, agreeing to sell off four planes to raise cash. Its cash position had dwindled to $170 million last December.
Its filing follows bankruptcy filings by Skybus Airlines, ATA Airlines, and Aloha Airgroup in recent weeks.
American, meanwhile, said late Friday that it had 231 of its 300 MD-80s back in service. It expects to cancel about 200 flights Saturday and run a normal schedule on Sunday, with all the MD-80s in service.
To cut costs and reduce payrolls, airlines have increasingly sent maintenance work out to contractors in recent years. Roughly two-thirds of maintenance was outsourced as of 2006, according to testimony last year by the Transportation Department's inspector general, Calvin L. Scovel III. That was up from a decade earlier, when about a third of the maintenance work was outsourced.
The FAA, however, has not moved as swiftly to shift its inspectors to monitor these hundreds of contractors, causing concern that the agency is not scrutinizing some of the highest-risk work on planes.
Much of the work is sent overseas. But at the time of Scovel's remarks before a House subcommittee, just 103 of the FAA's 3,865 inspectors were devoted to international field offices.
"The issue is not where maintenance is performed but that maintenance requires effective oversight," Scovel said.
Domestic carriers have bought few new planes in recent years, and their fleets have aged, hitting an average of 12.2 years at the end of 2006, versus 10.6 years at the end of 2002.
Only two domestic carriers, Northwest Airlines and Continental Airlines, have orders in for the fuel-efficient Boeing 787, while dozens of overseas carriers have ordered the plane. And even if domestic carriers made big orders today, they would have to wait because Boeing and Airbus are booked solid for years.
The disclosure in recent weeks of breakdowns in compliance with government safety directives at Southwest Airlines and American is helping to create an odd coalition of groups calling for stricter regulation of airliner maintenance.
Consumer aviation advocates, some airline labor unions, and a group representing corporate travel departments are among those calling for stricter control over repairs.
Kevin Mitchell runs the Business Travel Coalition, representing travel departments of major corporations, not traditionally a group given to calling for increased federal regulation.
But he has managed to get scores of major companies--McDonald's, Accenture, and R. J. Reynolds among them--to sign a letter to Rep. James L. Oberstar, Democrat of Minnesota and chairman of the House Transportation and Infrastructure Committee, asking for a stronger FAA.
"When exposed to an increasingly unforgiving marketplace, some airlines will subordinate passenger safety to other commercial priorities, just to survive," the group's letter said. "That's why there is a federal regulator."
The group is particularly distressed about the increase of outsourced work to overseas contractors, and the FAA's failure to shift resources rapidly to monitor the work.
"There's nothing wrong with outsourcing," Mitchell said. "It's a useful business practice." But the inspectors need to follow the work and scrutinize it as carefully as work done at airlines, he added.
Mitchell on Friday called for the removal of the FAA's acting administrator, Robert A. Sturgell. "The traveling public has had its trust broken," Mitchell said.