PARIS—Boeing is revising the 777X test plan to maximize ground evaluations as it attempts to compensate for a lengthy delay to first flight following the recent discovery of a durability issue on the aircraft’s General Electric GE9X engines.

“The long pole in the tent remains engine issues identified during aggressive testing of the GE9X under rigorous operating conditions. We are staying very close to this situation as it evolves,” Boeing Commercial Airplanes president Kevin McAllister said.

Boeing initially hoped to begin the 777X flight test program in March but after other program delays earlier in 2019 slipped the target date to late June. However, GE will require several months to develop and test fixes to the engine and first flight now looks set to be more likely in the October-November time frame.

The engine problem cropped up during a 150-hour certification endurance block test. The fix will involve improvements to the stator vane in the second stage of the high-pressure compressor.

The modifications are expected to be complete “later in the fall,” GE Aviation Commercial Engines VP and general manager Bill Fitzgerald said.  “Boeing then will decide when we are going to fly.” The upgraded stator configuration, which will represent the certifiable bill of material, will be retrofitted on eight test engines and 10 flight compliance engines.

“We’re making the most of this time obviously and continuing to work to get it right for first flight with this airplane,” McAllister said. “There’s plenty of activity that we can pull to the left prior to our flight test program to make sure we address any opportunities to advance the readiness of the airplane before its first flight. And that’s exactly what we’re doing.”

Despite the hold ups Boeing said the 777-9 remains on track for first delivery in 2020, although this will clearly not occur until much later in the year than originally planned.