Development of the -1B engine begins in earnest with the first engine to test around the end of June 2014, followed by the start of flight tests on the flying testbed by the end of the first quarter 2015. Unlike the earlier Leap test engines, which will fly on GE’s existing 747-100 testbed, the 737 MAX engine will be flown on GE’s recently acquired, former Japan Airlines-operated 747-400.

FAR33 certification of the -1B is anticipated before the end of the first quarter 2016, providing margin before the planned start of 737 MAX flight tests.

Boeing officially says that these are expected sometime in 2016, though Aviation Week understands the timetable calls for the flight test program to start in the second quarter of that year.

Rather than the F101-derived core at the heart of the CFM56, the Leap engine series is based on an all-new core. Three core builds so far have been tested in support of the Leap effort, with a third due to start in the first quarter 2013. Further derivatives of the core, which is scaled to about 90% of the actual size of the Leap high-pressure spool, are planned beyond Core 3, says Richards. “We will be running a Core 4 and Core 5 to look at technology for the future. They need to be off the critical path, but will be used to support GE9X in particular (the engine in early development for Boeing’s proposed 777X), as well as for Leap future evolution,” he notes

Another question still hangs over the final thrust ratings for the Leap engine. The larger—1A and 1C—variants are expected to be defined in the same 33,000-lb.-thrust bracket as Pratt & Whitney’s PW1100G, while the -1B is widely expected to be configured around 28,000 lb. Boeing has yet to officially announce the targeted thrust, but confirms it plans to do so “before engine design freeze and before we reach firm configuration on the 737 MAX, which will be by mid-2013.”