There was a well-known airline saying that quipped: "Whether you go to heaven or hell, you'll have to change planes in Atlanta." Since 1998, ATL (now Hartsfield-Jackson International Airport) has carried more passengers than any airport in the world. In 2012 that's likely to change.

Several airports around the world have taken their turns being among the busiest on the planet --- London-Heathrow, Chicago, Hong Kong, Los Angeles. But with the rise in air traffic in Asia, one perennial passenger leader is about to be toppled. Atlanta (ATL) now offers barely 400,000 more seats than Beijing Capital International Airport (PEK). With ATL's 5 percent decline in passenger traffic for December 2011 and PEK's 4.5 percent seat capacity growth in the same period, the handwriting could be on the wall, or in the clouds.

The Asia-Pacific region has overtaken North America as the world's largest aviation market and airports in the growth areas are poised to overtake some of the best-known airports for passenger traffic. PEK surpassed London-Heathrow in 2010 to claim the spot as the second busiest airport in the world and now Tokyo's Haneda Airport (HND) which resumed international flights in 2010 has offered more seats than LHR so far this December.

Among cities with multiple airports, London still tops the list of world's busiest airport hub regions but even that title may have to be relinquished to Beijing or even Dubai in the coming years. In September, the Chinese government announced plans for a behemoth of an airport to be built in the Daxing district southwest of the capital. The airport will occupy a total of 54 square kilometers with nine runways and will give Beijing's collection of airports the capacity to handle nearly a quarter of a billion passengers a year – more than 2 or 3 times the current capacity at Heathrow.

2010 Rankings for world airport systems (cities with multiple airports):



Source: Airports Council International

Rankings of individual airports in terms of passenger traffic (through August 2011):



Source: Airports Council International