(FORTUNE Magazine) – That sound you hear coming from airline lobbyists is not a sigh of relief, even though Congress has decided to provide some aid and comfort to the beleaguered business. It is a death rattle. The aviation industry, as we have known it for decades, cannot survive. The choice is not even to change or die: Both things are going to happen. Within the next few years, at least one of the six major carriers--American, Continental, Delta, Northwest, United, or US Airways--will disappear. The rest must change radically. Congress cannot do it for them.

So should the Bush administration just let nature take its course? In a March report the Air Transport Association made the case for help. Aviation, the ATA argued, had been hit by a "perfect economic storm" for which it could not be blamed: terrorism, war, higher fuel prices, higher security costs, deflation, a weak economy. Put it all together, and the industry is on course to lose $10.7 billion. The case is compelling--up to a point. Yes, aviation taxes are too high. Yes, security costs should be distributed more widely. But even if Congress were to relieve those burdens, the industry would be in trouble.

The fact is, it takes perfect conditions for the airlines to make money. The last time the stars were aligned was 1997--2000--the bubble years, when the industry made more money than at any time since the dawn of flight. More typical were the first eight months of 2001. The economy was growing (albeit not very fast), and fuel prices and security fears were low; even so, the airlines were on course to lose $3.5 billion, a figure that rose to $7.7 billion after Sept. 11. In 2002, when extra security cost $4 billion, the industry lost more than twice that much.

That is more than bad luck. Simply put, the majors can't afford to do business in the style to which they are accustomed. United and US Airways had expenses of more than 11 cents per seat mile before they went into bankruptcy, vs. 7.4 cents for Southwest and 6.3 cents for JetBlue. United and American spent almost half their revenues on labor in 2002--at a time when more and more Americans prefer the cheap, cheerful ways of low-cost carriers, thus reducing demand for the high-priced service (often without a smile) of the majors.

United and US Airways have used bankruptcy to negotiate dramatically better terms with their unions, lenders, and aircraft lessors. American is using the threat of bankruptcy to do the same. That will increase the pressure on Delta, Continental, and Northwest, which are in better shape (Delta, in particular) but would have to adapt to the competition. Let the restructuring begin. --Cait Murphy