Now they are in chaos, with airlines grounding more than 500 planes and thousands of flights so far because they may not meet safety requirements. Travelers have seen this before but only rarely, when all planes were grounded after the Sept. 11 attacks and when the government grounded all DC-10s after an engine fell off one of them in 1979, killing 273 people.
But there is a big difference this time: there has been no crash.
What happened?
One answer is that some whistle-blower inspectors for the Federal Aviation Administration disclosed that they had been discouraged from cracking down on Southwest Airlines for maintenance problems, and they found a sympathetic audience with some Washington lawmakers.
That prodded the F.A.A. to order a national audit to check whether airlines were in compliance — and to propose a record penalty of $10.2 million against Southwest.
Then F.A.A. inspectors discovered the mistakes that prompted American to cancel more than 3,000 flights last week. Delta, United, Alaska and others also canceled hundreds of flights.
But more broadly, the turmoil is better understood as a reaction — or overreaction, in the eyes of some in the industry — to a long-term shift, over two presidencies, in the way the F.A.A. oversees the airlines.
In the 1990s, the agency was more of a cop on the beat, handing out penalties to those who broke the rules.
“You used to fear an F.A.A. inspector showing up,” said Joseph Tiberi, a spokesman with the International Association of Machinists and Aerospace Workers. “They checked everything from the nuts and bolts in your tool kit to the paperwork in the cockpit.”
But then a different, more collaborative approach emerged that critics say went too far. After the 2001 terrorist attacks, which crippled the industry, the agency began “a creep away from their rigorous oversight of maintenance,” said Representative James L. Oberstar, Democrat of Minnesota and the chairman of the House committee that has pushed the issue.
That arrangement was “coddling the airlines,” he added, which eased the burden on the F.A.A., with its inspectors spending more time on paperwork than on airplanes.
The change began after the T.W.A. 800 and ValuJet disasters in the mid-1990s, when regulators and the industry convened a “safety summit.” Then the Clinton administration formed a national commission in 1997 on aviation safety and security, led by Vice President Al Gore and known as the Gore Commission. It set a goal of cutting the rate of fatal accidents 80 percent over 10 years.
One idea was for the F.A.A. to start working more closely with the industry. If airlines shared their mistakes or problems without fear of retribution, the reasoning went, the system would benefit from these shared lessons.
And it seems to have. Over the next decade, the accident rate fell 65 percent, and this new approach is widely seen as having played a role in the drop.
Then the F.A.A., under the Bush administration, took on a role after the Sept. 11 attacks to help the industry recover — “through technology, through greater efficiencies, through sensible and non-burdensome regulatory schemes,” Marion C. Blakey, the F.A.A. administrator in 2002, said at the time. She declined to be interviewed for this article.
This more collaborative approach was reflected in a “customer service initiative” announced by the F.A.A. in April 2003.
The customers in this case were not passengers; they were the airlines the F.A.A. regulates. The core principles of the new initiative, which inspectors could print up on pocket-size cards, included creating for the airlines “an environment without fear of retribution if you challenge our decisions” and “clear guidance on how you can elevate your concerns to the next higher level of authority.”
The F.A.A.’s watchdog role, to many Democrats in Congress who now oversee airline regulators, grew toothless. “We had drifted a little bit too much toward the over-closeness and coziness between regulator and regulated,” said H. Clayton Foushee Jr., a former F.A.A. official who led a recent inquiry by Mr. Oberstar’s committee.
Some inspectors in the field were also concerned by the drift. In early 2003, Charalambe Boutris, an inspector in the F.A.A.’s Dallas office, began reviewing Southwest’s engine maintenance records.
The task would seem the equivalent of the Maytag repairman’s job, since Southwest has a stellar safety record. But Mr. Boutris discovered the airline’s record-keeping was inconsistent and varied from aircraft to aircraft, according to the United States Office of Special Counsel, which reviewed his accusations.
After raising the issue with a supervisor, Mr. Boutris was told he could send Southwest a letter expressing concern, but not a more serious “letter of investigation,” which is what regulations called for under such circumstances.