An issue with a compressor component in the GE9X is pushing back flight-testing aboard the Boeing 777X by several months to possibly this fall. GE Aviation, in concert with Boeing, “hit the pause button” on GE9X testing while it redesigns a stator in the front part of the compressor that had shown more wear than anticipated during testing, GE Aviation president and CEO David Joyce said Monday at the Paris Air Show.

Joyce added the company “feels confident” that the engine manufacturer will have the issue ironed out and the engine certified in time for flight aboard the 777X platform by year-end.

Boeing (Chalets 332, 335) is monitoring the situation closely, said Boeing Commercial Airplanes president and CEO Kevin McAllister, noting it is premature to discuss firm timing expectations for the 777X in light of the engine issue. “We need to get more findings from them to reassess the overall timing,” McAllister said, but he also expressed the belief that, based on what the companies know, “we still expect the airplane to flight test this year with an entry into service next year.”

Boeing had anticipated beginning test flying of the 777X shortly, with certification in mid-2020. But Boeing and GE Aviation decided to wait for a certified engine before beginning the 777X campaign. Joyce, however, stressed that the engine certification program is mature with 2,700 test hours and 4,000 cycles on eight engines. GE Aviation brought the massive engine—the first-engine-to-test article—to the Paris Air Show this week to display (Chalet A144).

The issue with the compressor component surfaced a little more than three weeks ago during what Joyce called “block testing” that is conducted near the end of the flight-test program. This testing brings the engine outside of the normal operating envelope, he added.

During these trials, GE discovered a shift in the exhaust gas temperature while other metrics remained “on point.” This prompted a closer look and the discovery of the prematurely worn stator. Once the problem began, GE Aviation and Boeing “together decided that we were going to redesign that component, go back and rerun the test that proves the durability…and then retrofit the engines.”

“We’re working pretty aggressively to go after a new design and getting a fix,” added GE Aviation v-p and general manager of commercial engine operations Bill Fitzgerald. Once a fix is in place, GE Aviation will need to swap out the component with a more “robust design” in eight test engines and 10 compliant engines.

Joyce said the fix was important to GE Aviation and Boeing to ensure that the engine did not need to enter maintenance earlier, raising costs of both the customer and the manufacturer.

In the meantime, McAllister said Boeing is making the most of the time “by continuing to get it right for first flight with this airplane. There is plenty of activity that we can pull to the left before our flight-test program to address any opportunities to advance the maturity of the airplane for its first flight.”