GE Aviation has delivered the first three fully compliant GE9X turbofans to Boeing’s Everett, Washington, widebody plant following retrofit of redesigned Stage 2 stator vane assemblies in the engines' compressors, GE9X program head Ted Ingling reported just ahead of the Dubai Air Show. Ingling explained that the process that led to the fix to the titanium part involved revamping the geometry to ensure a proper wear profile. With testing completed, GE has now retrofitted the fix on six engines, the fourth of which it was preparing to send to Everett when Ingling spoke with AIN on November 8.
In all, GE has built 10 compliant engines, eight of which will go on flying test airplanes, along with two spares.
While Boeing CEO Dennis Muilenburg said during the company’s recent third-quarter earnings call that the engine remains a “pacing item” for the new Boeing 777X, Ingling told AIN that the timing of the fix has not deviated from the schedule set for it when GE discovered the problem in late May. With both engines now mounted, the first 777X awaits final installation work and on-wing testing before making its first flight, scheduled now for the first quarter of next year. As a result of the engine delay, Boeing has moved the airplane’s certification target from late this year to early in 2021. “We continue to explore opportunities to improve the timeline such as leveraging our system integration labs and additional airplane ground testing,” said Muilenburg.
GE’s stator vane fix involved what Ingling called some geometrical changes outside of the flow path, meaning engineers did not alter the aerodynamics of the design. “So that, number one, is paramount to hanging on to our performance and our operational characteristics,” said Ingling. “So it didn't need to change. It was the boundary conditions around it that had to change.”
Although GE halted certification testing while it devised the stator vane fix, maturation testing continued unabated. “We had certification vehicles we had to incorporate into our development vehicles as we continued to prepare the engine for entry into service,” explained Ingling. “We're doing the final couple of certification tests to finish that up. We halted those while we were waiting for this fix.
“And then we have our maturation testing that we continue to do...we put some of that in between a couple of the compliance engines. We introduced our maturation engine with the fix in it so we can keep the maturation program going on. We have a fleet leader that keeps our knowledge points of the engine way ahead of the field as a means to help smooth out anything that might show up in the engine in service.” Ingling said testing on the maturation article would start soon.
Of the eight engines GE runs in its suite of development vehicles, seven participate in certification validation, software development, and Part 25 testing, all the while incorporating lessons from earlier programs to enhance capability. “So we use these vehicles to validate that those solutions are effective in the 9X,” explained Ingling. “In fact, we got asked questions about non-GE or non-CFM engines in terms of these kinds of issues to make sure that we've got them resolved. And we have been systematically validating that every one of those items has been addressed and we're closing in on the final validations as we speak.”
Asked to name the biggest challenge the program presented, Ingling conceded that the stator vane problem took him and his team by surprise. The fact that the company discovered it fairly late in the process proved “troubling,” he said, notwithstanding the fact that such hurdles often present themselves during development of a new centerline engine. “This particular one came at us a little late in the program,” he lamented. “And the nature of it required us to get inside the engine to fix it. And that, by definition, given when we found it and where we found it, drove the schedule. I will say it’s unfortunate from a schedule standpoint, but fortunate from a product standpoint. I much preferred to find this in a place where we could fix it and robustly get it behind us than to have something show up in flight tests or certainly in the field.”
Overall, Ingling expressed satisfaction with the program’s ability to consistently meet performance criteria, thanks to lessons learned from earlier programs. In fact, he said, engineers could have extracted still more performance from the engines if they “threw the kitchen sink at [it],” possibly at the cost of durability.
“We spent a lot of time and a lot of money early on in this development program before we ever had the first engine in our rigs, making sure that we had the building blocks of the performance well sorted out because that has not always been the outcome that we get with a new centerline engine,” explained Ingling. “It was anything but easy in the early days trying to get all the components done. But that really paid off in a product that didn't require us to think about any changes aerodynamically to restore the performance that we were looking for.”