Earlier this week, the Seattle Times had a great story on Boeing’s 737 MAX.

Marking a milestone at its Renton factory, Boeing on Friday began assembling the wings of its first 737 MAX.

While work progresses on the the first of specimen the new model 737 series, Boeing is accelerating production of the old.

The Renton factory is churning out more airplanes, 42 jets a month, than any factory in the world. Even as the MAX is introduced into production, the plant is preparing to ramp up to 47 jets per month in 2017 and then 52 jets a year later.

The first 737 MAX should be completed by year end and enter flight testing early in the new year. The company plans a smooth from the old to new models.

The MAX initially will be built in Renton on a separate production line that will work slowly at first, allowing the assembly team to learn and perfect the MAX build process while the other two assembly lines roll out the current models at an ever more frenetic pace.

Boeing’s website currently shows 4,170 unfilled orders for the 737; 2,725 of these orders are for the 737 MAX.