GE Aviation still anticipates completing GE9X certification testing this year after a lengthier-than-planned round of flight tests and recently discovered "anomaly" in an engine's high-pressure compressor.
GE Aviation completed a second round of certification flight testing for the 777X's engine in May, during which it completed 53 test flights and logged more than 300 flight hours.
The engine maker had told FlightGlobal late last year that it anticipated "making about 18 flights or so" during the second round of testing.
That was about the same number as in the first testing round, which concluded in May 2018.
The company says additional flight tests in the second phase reflect changes to the massive, 105,000lb-thrust (467kN) GE9X's "variable stator vane lever arm".
The arms set the pitch of stator vanes, which are inside the compressor and slow airflow, increasing its pressure. GE Aviation redesigned the arm prior to the second phase of test flights after determining the initial design wore out faster than expected.
"Since the engine for phase two had the new variable stator vane lever arm in the high-pressure compressor, we wanted to get the engine performance data on this configuration at altitude," GE Aviation says.
It also repeated some tests conducted in the first phase of flight testing. "The engine performed extremely well on the flight tests," GE Aviation says.
GE Aviation tests the GE9X on its 747-400 flying test bed
The company is making other changes to improve the GE9X's durability.
"During a recent test, GE detected an anomaly in the engine data from the high-pressure compressor," GE Aviation says. "After data analysis and additional testing, our engineers saw an opportunity for a durability improvement in the front of the compressor."
"GE anticipates completing its certification testing this year," it adds.
The company does not provide specifics, but says the anomaly is "mechanical in nature — and is not related to the design or performance of the high-pressure compressor".
"GE is taking a proactive approach and working the improvement so it can be incorporated into the flight test engines at Boeing as well as incorporated into our engines that will take part in our remaining ground tests," the company says.
GE Aviation has completed about 85% of the GE9X's certification testing, including aerodynamic, bird-ingestion, loss-of-blade, hailstorm and icing tests.
"The engine's performance at altitude was great," GE Aviation says. "Just a handful of tests remain, including emissions and block test."
The block test involves running the engine for 25, six-hour cycles, accumulating 150h of run time during which the engine is at "redline" – its max core speed, fan speed and exhaust gas temperature, GE Aviation says.
The company conducts GE9X flight testing on its 747-400 test bed.
Last week Boeing chief financial officer Gregory Smith said Boeing was waiting on the GE9X to advance the 777X programme.
"Long-pole in the tent right now is [the] GE engine. There are some challenges. They're working through their own testing," Smith said of GE Aviation during an investor conference hosted by investment bank UBS. "We're having to do some retesting. And they're working their way through that."
"We still expect to fly this year and entry into service in 2020," Smith added.
Boeing installed GE9Xs on its first flight-test 777X in January. The engine's 3.4m-diameter (134in) fan, composed of 16 carbonfibre blades, makes the GE9X the world's largest jet engine, GE Aviation says.