Many airlines are facing tough conditions as consumers and businesses in austerity-hit regions cut back on travel, while high fuel prices are taking their toll on profit.

"I don't think there's any question that the forecast reflects the economic struggles we see today in some of the mature markets," Randy Tinseth, vice president marketing at Boeing Commercial Airplanes, told a media briefing in London.

The forecast did not take into account a possible collapse of the euro or the exit of any euro member, Tinseth said.

"We're looking at a world economy, where, especially over the next few years, we slog through the situation here in Europe and then once you get into the 2014 time frame and beyond, you see more normal economic growth."

Boeing (BA.N) said on Tuesday the market for new planes would become more geographically balanced over the next two decades, with the Asia-Pacific region leading the way in deliveries, as markets like China and India continued to grow.

The company had last year forecast demand for 33,500 new passenger aircraft and freighters worth $4 trillion by 2030.

"Robust growth in China, India and other emerging markets is a major factor in the increased deliveries over the next 20 years," Boeing said.

The company said airline traffic was forecast to grow at a 5 percent annual rate over the next 20 years, with cargo traffic seen growing at a rate of 5.2 percent.

It saw the world fleet doubling over the next two decades.

"Low-cost carriers, with their ability to stimulate traffic with low fares, are growing faster than the market as a whole," the company said.

REPLACEMENT AIRCRAFT

Boeing said there was strong demand to replace older, less fuel-efficient aircraft, with replacements accounting for 41 percent of new deliveries in the forecast, which runs to 2031.

There would be strong demand for replacement aircraft from Europe, the United States and Russia, Tinseth said.

The Chicago-based company said it saw a market for 23,240 single-aisle aircraft over the next two decades - a category that includes its 737 and rival Airbus's (EAD.PA) A320 - worth $2.03 trillion.

It predicted demand for 7,950 twin-aisle aircraft - such as its 787 Dreamliner - worth $2.08 trillion and 790 large aircraft - the Airbus A380 or Boeing 747 - worth $280 billion over 20 years.

Two fifths of the demand for widebody long-range aircraft would come from Asian airlines, Boeing said.

It cut its forecast for the freighter market, blaming a cargo market that remains sluggish. It said it expected the world freighter fleet to nearly double from 1,740 aircraft today to 3,200 by 2031. Last year it had forecast the fleet would reach 3,500 by 2030.

That market segment was flat last year and would perform below the long-term trend once again this year, hit by economic problems, high fuel prices and the fact that lower cost alternatives like shipping exist," Tinseth said.

"That market's going to come back when the economy comes back," he added. (Editing by Dan Lalor and Hans-Juergen Peters)

• A Permanent Economic Emergency