Chicago's 233 S. Wacker Drive had a rough day Nov. 12, when it comes to titles.
That's the day the building, better known as Willis Tower and the former Sears Tower, officially lost its title as America's tallest building -- to be surpassed by 1 World Trade Center when it opens next year in New York.
On the same day, United Airlines, which makes its headquarters in Willis Tower and is the building's largest tenant, learned it will lose its claim as the world's biggest airline. That came when antitrust regulators dropped a lawsuit objecting to the merger of US Airways with American Airlines, which will end up bigger than United.
Indeed, even on its home turf of O'Hare International Airport, the new American could challenge to be a larger airline than United for domestic flights, and it already is by some measures.
The effect on United in Chicago is just an example of the fallout from a dramatic reshaping of the airline landscape in recent years -- in America and around the world. In the U.S., the metamorphosis has left just three major airlines -- American, United and Delta Air Lines -- along with one formidable low-cost carrier, Southwest Airlines.
It's the fulfillment of a decades-old prophecy that the U.S. airline business could support only three major airlines. And it likely marks the end to a wave of major-carrier consolidation that has helped put U.S. airlines on more sound financial footing.
Could the U.S. airline industry finally have reached a healthy equilibrium that is better for the airlines and for its customers?
Some airline experts think so.
"If we can get to an industry that is financially stable, that is operating more of its flights on time, that treats its people better through greater job security, then ultimately the passenger benefits," said Henry Harteveldt, a travel industry analyst at Hudson Crossing.
Now that the Department of Justice has exacted some concessions from the airlines and dropped its antitrust lawsuit last month, the $17 billion merger between AMR, parent of American Airlines, and US Airways Group can go through, and it is expected to close Monday. American, which has been in bankruptcy for two years, cleared the final hurdle Nov. 27 by receiving the OK in bankruptcy court.
Passengers will begin to notice merging of the carriers Jan. 7, when the airlines plan to begin acting like a single airline, offering reciprocal frequent-flier benefits, for example, executives have said.
The combination ends a spate of recent airline consolidation, spurred by a weak economy and billions in industry losses, starting with Delta and Northwest agreeing to combine in 2008. That was followed by United/Continental and Southwest/AirTran.
Now, the three majors and Southwest will control about 85 percent of the U.S. market.
It's a result that was totally expected.
The "Rule of Three" management concept posits that three is the magic number for competitors in a mature market, according to a recent report, "Aviation Outlook," by management consultant ICF International of Fairfax, Va.
" 'Room for three only' has been the universal prediction since the 1980s as flying became affordable and airplanes could take you nonstop almost anywhere. By 2014, in the United States at least, it will finally happen," the report says.
The idea is that three is not too many competitors to perpetually fight and not too few to get greedy.
Europe also has three majors -- Air France-KLM, British Airways and Lufthansa -- as do Latin America, China and the South Pacific. There are three worldwide airline alliances, the report notes.
But the Rule of Three concept isn't clean when applied to the U.S. airline market. That's because of Southwest, which is the largest domestic airline in the U.S. as measured by number of passengers carried.
But Southwest is considered a low-cost carrier, not a direct apples-to-apples competitor with the three majors in terms of having an extensive route network, especially to international destinations. It doesn't offer luxurious first-class amenities, and it doesn't fly to quite as many smaller destinations as major network carriers do via their regional carrier partners.
"Three -- or call it four -- giant airlines are completely supportable and don't sit on top of each other for every nonstop," said Subodh Karnik, a vice president at ICF and former CEO of the now-defunct ATA Airlines, which once had a dominant base at Chicago's Midway Airport.