In 2011, Airbus and Boeing took orders for 2,529 aircraft, their highest combined total since a record 2,881 orders in 2007, just before the global economy went into meltdown. On July 3, Boeing released its 20-year commercial aircraft market forecast for 2012 through 2031. It predicted an increase to 34,000 new aircraft, costing $4.5 trillion and doubling the global fleet, based on a combination of emerging market growth and the need for more fuel-efficient planes. That compared with its forecast a year ago of 33,500 new aircraft in the two decades through 2030. Both Airbus and Boeing come to the Farnborough International Airshow, outside London, this week with bulging order books for their single-aisle airliners. Yet the signals for the aviation industry and its aircraft suppliers are at best mixed, at least in the near term. In the United States, recovery from the 2008-9 financial crisis and recession has proceeded slowly, in fits and starts, and the economic outlook remains uncertain.