Boeing has confirmed it will build a third assembly line for its 737 MAX jet family alongside one of the two existing lines in Renton, Washington.
The jetmaker also said it had refined the plane's design, adding better visuals for pilots and a slightly smoother fuselage line.
"The 737 MAX factory integration plan is now final," said Michael Teal, chief project engineer on the 737 MAX program, in a media teleconference on Thursday.
Space for the new third line will be created mostly by moving and compressing the feeder lines and parts-storage areas now covering the floor alongside one of the current lines, said MAX program manager and Vice President Beverly Wyse.
Within the next five years, the company will hire hundreds of new production workers to staff its burgeoning Renton assembly lines and will also add hundreds of engineering jobs for the MAX.
The 737 currently is built at a rate of 35 per month. That rate is going up to 38 per month in the second quarter of next year, and to 42 per month a year later.
Those increases will be accommodated on the two existing lines, which by 2014 will each be rolling out slightly more than one jet per day.
Wyse said the third line will allow Boeing to smoothly introduce the initial jets of the new MAX model, which will inevitably be built more slowly.
Later, she said, it could be used to increase the rate beyond 42 per month.
"We don't have specific plans on the next rate increase," Wyse said, "but we're pretty sure it's coming".
The first four jets built on that third assembly line, starting in 2015, will be 737 MAX 8 flight test lanes, with lots of flight test instrumentation installed on the assembly line.
Later, Boeing will build four more test flight jets for the two subsequent MAX 7 and MAX 9 models.
On Thursday, the jetmaker declared it had achieved "firm concept" on the MAX design, defining all the significant changes needed to deliver the 13 per cent improvement in fuel economy promised to airlines.
The latest features add to the previously announced MAX design, which includes new fuel-efficient LEAP-1B engines from CFM International, raked "dual feather" winglets and a redesigned tail cone.
Wyse said the program is on track to deliver the first MAX jets to airlines in late 2017.