RENTON, Wash. -- Boeing's newest 737 is getting close to heading out the door of the factory here that continues to build the world's most popular airliner.

The 737 MAX 9 promises more range than the Next Generation (NG) 737-900 it will replace.

The MAX 9, set to head out by the end of February, says Keith Leverkuhn, vice president and general manager of the 737 MAX program. Leverkuhn also says the company continues to study going one better -- a MAX 10 -- which some regard as a partial replacement for a 757. Boeing stopped producing the 757 in Renton in 2005. The MAX 10 would be 66 inches longer than the MAX 9.

The MAX 9 will enter flight test for about nine months, involving two planes. But the first of Boeing's 737 MAX airplanes is almost ready for delivery after extensive flight testing following its 2015 rollout. Certification of the MAX 8 should be ready by the end of March, says Leverkuhn.

The wide-body market is in somewhat of a slowdown, including Boeing's 777 which is being upgraded to the 777X in Everett. At the same time, the so-called single-aisle market, that also includes the Airbus 320 series, continues to rack up orders. That is promising for long-term employment for Boeing workers in Renton and the company's presence in and around Seattle.

In a tour of the new wing factory, Boeing showed off automated tools that make the spars for the 737. The tools are made by Mukilteo's Electro Impact. The spar provides much of the strength for a wing, kind of like an I-beam in the front and the back, to which the skin and other parts are attached. The company's upgraded wing factory can make wings faster and use less space than the older technologies.

Boeing has some 3,600 737 MAXs on order, it also expects to keep producing NG models into 2020. In 2017, 10-15% of the planes delivered to airlines will be MAX models alone.

All of this goes to how fast the company is making the planes. Boeing is currently making 42 of the airplanes per month. That rate expected to fully reach 47 airplanes per month by the end of the year. The plan is to go to 52, then 57 airplanes per month.