SEATTLE (Reuters) - Boeing Co BA.N said on Tuesday it plans to fly its new 737 MAX-9 aircraft for the first time in April, a further sign the company will start delivering the large version of the workhorse plane in 2018.

Slideshow ( 12 images )

Delivery of the single-aisle 737 MAX models, which replace the current 737 “NG” introduced in 1997, is crucial for Boeing to hit the financial targets it has promised investors and to offset slowing output of some of its largest jets such as the 777 and 747. Airlines want the MAX because it burns significantly less fuel than current models.

The world’s largest plane maker is creating up to five MAX versions, while planning to increase output to 57 planes a month in 2019, from 42 a month at present.

The first MAX model in production, known as the MAX-8, is on track to reach customers by mid-year.

“We are anticipating our certification of the airplane within a matter of days-weeks,” Keith Leverkuhn, 737 general manager, said at a Monday briefing embargoed until Tuesday.

The stamp of approval by the U.S. Federal Aviation Administration would come about a year after the MAX-8’s first flight and allow Boeing to begin delivering the $110 million, 162-seat jetliner in the second quarter, he said.

Deliveries trigger the bulk of airline payments. Norwegian Air Shuttle NWC.OL will be one of the first airlines to fly the plane commercially, likely ahead of launch customer Southwest Airlines Co LUV.N, which was first to order the MAX but is taking longer to put it into service.

Boeing expects the MAX to account for as much as 15 percent of the 500 or more 737s it expects to deliver in 2017, rising to nearly 100 percent by 2020.

Boeing on Monday showed off the first 737 MAX-9 sitting near the end of the assembly line at its factory in Renton, Washington. The nearly completed jet, which carries a list price of $116.6 million and seats 178, will undergo about nine months of testing after first flight in April.

MAX-10 TAKES SHAPE

Boeing is mulling an even larger version, the 737 MAX-10, to take on rival Airbus AIR.PA, which has had strong sales of its A321neo that is a larger competitor to the MAX-9.

The MAX-10 would be 66 inches (1.68 m) longer than the MAX-9, with the same engine thrust. The major change will be the landing gear, which must be taller to accommodate the longer fuselage.

Boeing expects to test various landing gear designs this year “to see which one ... is going to be the best solution,” Leverkuhn said.

Boeing is about 90 percent finished with design drawings for the smallest version, the 737 MAX-7. A high-density MAX-200, with seating for 200 passengers, rounds out the model line.

Sales of Boeing’s larger twin-aisle planes have slowed sharply and the company is cutting output of the profitable 777 by 40 percent this year. It will rely on the 737 and 787 to make up a large part of the financial difference.

Introducing new models while increasing production rates requires Boeing to solve any factory issues quickly. So far, Leverkuhn said, “the hours to build the MAX are meeting our expectation.”