Boeing’s manufacturing team in Renton, Washington, has begun work on the first 65-foot wing spar for the 737 Max 7, marking the start of production of the latest Max variant in the five-member family. Scheduled for delivery in 2019, the Max 7 seats as many as 172 passengers and flies to a range of beyond 3,800 nautical miles. In a standard two-class configuration the airplane seats 152.

Although Boeing does not reveal order numbers by subvariant, the Max 7 so far has drawn the smallest proportion of the 3,900 total for all the Max models. Its two biggest customers, Southwest Airlines and Canada’s WestJet, had placed firm orders for 30 and 25, respectively, although WestJet reserved the right to convert its orders to positions on other variants. In fact, market analysts often describe the Max 7 as a niche product, offering what Boeing calls exceptional performance at high-elevation airports.

A special high-altitude performance package will allow airlines to serve hot-and-high airports with no loss in range or passenger count, according to Boeing. Features include higher thrust CFM Leap-1B engines than those that power the standard Max 7, advanced avionics for RNP AR, a gaseous oxygen system with up to 12 cylinders, alternative forward center of gravity for increased takeoff weight and an auxiliary battery with 60 minutes of standby power.