By Alwyn Scott
NEW YORK, July 10 (Reuters) - Boeing Co made its most bullish 20-year forecast for jetliner demand since 2011, saying on Thursday the world will need 36,770 new planes worth $5.2 trillion by 2033.
The company's annual projection is up 4.2 percent from its 2013 forecast, and it predicted beating rival Airbus Group NV in the lucrative market for twin-aisle planes as the planes are built and delivered over the next two decades.
"If Airbus doesn't do something with their product strategy, they're headed to 30-35 percent market share" in deliveries of next-generation twin-aisle aircraft, Randy Tinseth, Boeing's vice president of marketing, told reporters in a briefing.
Boeing's 787 and 777X jets already make up 65 percent of all current orders, with the Airbus A350 accounting for the rest, and that gap will widen unless Airbus develops another jet as a competitor, he said.
Planes are delivered years after orders are placed, so the final numbers may change as airlines change their plans.
Airbus has disputed Boeing's numbers, saying it is already winning most orders in twin-aisle aircraft when looking at recent years.
Airbus is considering embarking on development of such a jet, and may launch the project at the Farnborough Airshow next week. The jet, dubbed the A330neo, would be a revamped version of Airbus' twin-aisle A330 jetliner with new efficient engines made by Rolls-Royce Holdings PLC.
Boeing's annual forecast, released in conjunction with the airshow, said single-aisle airplanes such as the 737 and A320 will garner the most orders, reflecting booming demand for air travel in Asia and the growth of low-cost carriers there.
Last year Boeing predicted a 20-year need for 35,280 planes valued at $4.8 trillion.
About 40 percent of single-aisle planes built in the next two decades will go to low-cost carriers, and a large share of will be in China, Tinseth said. He predicted China would overtake the United States as the world's largest domestic air travel market in the next 20 years.
Twin-aisle planes also will attract strong demand. But Boeing notched back its forecast for jumbo jets such as the Boeing 747 and Airbus A380. It expects airlines to need about 620 of those over the next 20 years, down from the 760 it forecast last year.
"That's the market that has really struggled to take hold," Tinseth said.
Boeing expects airlines to buy 25,680 new single-aisle planes over 20 years, and that the global fleet will double to 42,180. About 58 percent of those planes will represent growth at airlines. The rest will replace retired aircraft.
Boeing cut its forecast for air-cargo growth this year to 4.7 percent from 5 percent in 2013, but said the trend is stable and will continue to support production of the 747-8 freighter and freight versions of its popular 777 jet.
(Reporting by Alwyn Scott; Additional reporting by Tim Hepher in London; Editing by Richard Chang)