In its latest world commercial helicopter market report, research firm Frost & Sullivan expects the ­segment to expand from 24,625 helicopters in 2009 to 36,946 in 2015. According to Frost & Sullivan aerospace analyst Nathan Smith, about 50 percent of the 12,321 ­helicopters will be light piston and turbine singles, while light and intermediate twins will each account for about 22 percent and heavy multi-engine helicopters will make up the ­remainder. Worldwide civil helicopter fleet growth declined from double digits in 2007 to 7 percent in 2008 and 5.7 percent last year. Lower demand and production levels are expected to persist into 2011 or 2012 before returning to double digits, the firm said. It estimates that over the next five years up to 22 percent of total world new rotorcraft sales will be to customers in Asia Pacific, Africa and the Middle East.