CFM, which has carried its sole-provider status for Boeing’s narrowbody programs to the new 737 MAX project, is closing in on final design for the Leap-1B powerplant chosen by the U.S. airframer.

“We think we’ve got the right architecture, and the more we go into it and the closer to defining the design, we feel more comfortable with what we’ve chosen,” says CFM Executive VP Chaker Chahrour of the Leap-1B, which will provide around 11% of the MAX’s overall 13% fuel burn advantage over the current 737, when other factors are considered.

CFM is on track for freezing the engine design, or the Toll Gate 3 milestone, in September and is set to begin the detailed design phase in the second quarter of 2013.

The first full Leap-1B will start tests in the second quarter of 2014 with the aim of achieving Part 33 engine certification in the first quarter of 2016.

This is designed to provide ample margin for flight tests of the 737 MAX and its planned entry-into-service in the second half of 2017.

Boeing has indicated, however, that it may try to accelerate the debut of MAX by several months, and Richards says, “We’re studying that, and if they ask for a faster schedule path, we will support it.” However, the existing development plan has “some margin” should Boeing “pull in” service entry, adds Chahrour.