Southwest Airlines on Wednesday gave Boeing the first orders for the smallest version of the new MAX jet family, the 737 MAX 7, by converting an order for 30 existing 737 models to the forthcoming version.

Southwest also added a new firm order for delivery next year of five of the existing model 737-800s.

At the same time, the airline pushed out the delivery dates for a total 28 of its 737 MAX 8 jets beyond 2021.

Southwest Chairman and CEO Gary Kelly said those deferrals will reduce near-term capital spending by more than $500 million.

Boeing now has 1,315 orders for the MAX, so the postponed deliveries won’t be problematic. Opening up those delivery slots prior to the end of the decade may actually help Boeing land some new MAX orders.

The MAX 7 seats 126 passengers in two classes. The MAX 8 seats 162, and the MAX 9 seats 180.

Some analysts had recently expressed doubt about the viability of the MAX 7.

“Should Boeing Bother to Build the 737-7 Max?” was the headline on a note last week from aviation consulting firm AirInsight.

Both Airbus and Boeing have seen a dearth of sales in this size category in recent years as airlines, including Southwest, chose to go up a size when ordering new jets.

The imminent arrival of the Bombardier CSeries jet, a new, very fuel-efficient competitor in this size class, also may be chilling sales of both the MAX 7 and its Airbus rival, the A319neo.

Bombardier’s CS100, seating 110 passengers, is to make its first flight next month and to enter service with airlines next year.

As of March 31, from a total of more than 2,000 firm orders for the Airbus A320neo family that competes with Boeing’s MAX series, just 45 were for the A319neo.

Boeing Commercial Airplanes CEO Ray Conner praised Southwest’s role as the premier customer for the 737 family. It was Southwest that officially launched the MAX family with an order for 150 jets in December 2011.

That tally now notches up to 180.

”We are excited to bring the 737 MAX 7 to market with Southwest,” Conner said in a statement.

Dominic Gates: (206) 464-2963 or dgates@seattletimes.com