Baku, April 14, AZERTAC

A new version of Boeing Co's (BA.N) 737 jetliner took off for the first time on Thursday, marking another step in Boeing's revamp of its best-selling product line that could see up to five new models introduced by 2020, according to Reuters.

Boeing's 737 MAX 9, a fuel-efficient, long-range successor to the 737-900, made its initial flight, a test mission, about 50 years after the 737 first took to the skies on April 9, 1967, and follows the first flight of Boeing's largest Dreamliner model, the 787-10, last month, from its factory in South Carolina.

The new models are coming to market just as demand for aircraft has slowed. Boeing has committed to making four new 737 versions and is considering a bigger version than the MAX 9, known as the 737 MAX 10X.

It could begin delivering that version in 2020 if airlines start ordering it this year, with China emerging as a promising market, said Michael Teal, 737 MAX chief project engineer and deputy program manager.

With the MAX 9 in the air, Boeing is turning more attention to the larger version. It began pre-marketing the plane this year but has yet to formally launch development of the jetliner, which would compete against the popular Airbus (AIR.PA) A321neo.

Teal said the design of the 737 MAX 10X would be firmed up by the end of this year and customers could receive the aircraft in 2020, depending on orders.

"We'll determine (the delivery date) when we launch that program when the customers show the interest and they buy the airplane," he said on a conference call with reporters.