Airbus and Boeing Co. are cranking up jetliner deliveries just as new turmoil hits financial markets and economic upheaval continues to threaten airlines and plane makers alike.

Yet there’s cautious optimism among the people who put planes in the air. Not pilots or engineers. The real power sources behind jets are the money managers who fund aircraft purchases and lease the planes to airlines. Many of them are gathering this week in Barcelona for the annual European meeting of the International Society of Transport Aircraft Trading.

Airplane financiers see opportunity because air traffic remains robust in many parts of the world, and high fuel prices are prompting carriers to replace old gas-guzzling planes with newer fuel-efficient models. Such demand is likely to continue. In recent months, such carriers as AMR Corp.’s American Airlines, Delta Air Lines Inc. andAir France-KLM SA have committed to order hundreds of planes, mostly to modernize their fleets.

“Demand for new aircraft over the next several years is exceeding supply,” says John Plueger, president of Air Lease Corp.

While demand remains strong, it’s another question whether airlines can muster the cash to pay for planes when they roll out of the factories. Taking ownership of a new jetliner usually entails paying Boeing or the Airbus unit of European Aeronautics Defence & Space Co. tens of millions of dollars. That generally requires some kind of financing, which has tightened significantly in recent weeks, airlines and airplane lessors say.

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