PARIS — Boeing’s big new 777X jet, which first rolled out of the Everett assembly plant in early March, cannot fly until at least the fall because of a problem with the new GE9X engine.

The long delay is a blow to Boeing, already struggling to cope with the crisis in its single-aisle 737 MAX jet program. It threatens to postpone the plane’s entry into service, planned for the middle of next year, and will hit both Boeing’s airline customers and suppliers.

In a revelation that stunned journalists at the Paris Air Show, Bill Fitzgerald, the head of commercial jet engines at GE Aviation, said his engineers already have a fix. But extensive testing is required for certification of the engines before retrofitting the fix to the 18 engines already completed, 10 for flight tests and eight for production models.

Boeing won’t fly the 777X until the engine is certified, said GE Aviation chief executive David Joyce.

Fitzgerald said GE will “be in a position to complete the testing by the end of the year and have the plane fly by the end of the year.”

“We’re pretty confident we’ll get through the testing this year,” Fitzgerald said, then added what seemed to be his current thinking on the earliest it can be ready: “It’ll be later in the fall.”

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Only after that can Boeing decide when it is going to fly the plane, he said.

That delay is far longer than anyone was anticipating, including the leadership of Gulf carrier Emirates, the first customer of the 777X.

In an interview with The Seattle Times on Saturday, Emirates president Tim Clark said that he’d initially heard first flight had been pushed out to June 29, but that had slipped. He said then he hoped it would fly before he gets to Seattle to review the program in mid-July.

If it hasn’t, Clark said, that will begin to squeeze his timeline, which depends on taking delivery of the first 777X next June.

That now looks unlikely. It typically takes a year or more to go from first flight, through the certification of the airplane by the Federal Aviation Administration (FAA), to entry into service — assuming there are no unexpected hitches. On the 737 MAX program, for example, the plane entered commercial service 16 months after first flight.

Both GE and Boeing tried to play down the impact.

Ted Ingling, the general manager of the GE9X program, said Boeing has “always had a plan to get the 777X off the ground by the end of this year.”

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“We’ll meet that plan,” he said.

Likewise, in a press conference Monday in Paris, Boeing Commercial Airplanes chief Kevin McAllister framed the delay as “an opportunity to advance the maturity of the airplane before first flight.”

“We still expect to have the airplane in flight test this year and enter into service next year,” he said.

But at the 2017 Dubai Air Show, Boeing specifically declared a delivery date for Emirates of mid-2020, not just “next year.”

What’s up with the engine?

The GE9X engine, the largest jet engine ever built, is an awesome piece of intricate machinery and advanced technology. It’s 134 inches in diameter, and the Boeing engine pods that encase it on the 777X are 184 inches at the widest point.

GE said that during testing the engine at one point generated a world record 134,000 pounds of thrust, well above the specified thrust requirement.

Joyce said the problem was discovered in the final phase of certification testing, when a gas turbine jet engine is run for a long period under extreme, beyond-normal conditions and its performance is carefully monitored.

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During that testing, about three weeks ago, he said, a sudden change in exhaust gas temperature signaled a problem. When the engine was taken apart, engineers could see the cause: excessive wear on a set of titanium parts inside the engine’s compressor section, where the air sucked in from the fan is squeezed to high pressure before combustion.

The parts are called stators, small stationary vanes on the perimeter of the engine core that together with the engine’s spinning turbine blades direct and compress the incoming air flow from the big fan at the front. An array of stators lines the inside of the compressor.

Joyce said the excessive wear indicated the parts were not durable enough, “which means the engine won’t be as durable, which means the airlines will have to pull the engine prematurely and put it in the shop” for maintenance.

To fix this, GE has already designed a more robust replacement stator, he said. But now it must manufacture the new parts, put them through lab tests, and then install the upgraded parts on an engine and repeat the same extreme testing that found the problem so as to demonstrate that it’s fixed and meets design requirements.

For certification purposes, all this must be accomplished with meticulous documentation of every step to satisfy FAA regulations.

Japanese suppliers surprised and concerned

Boeing’s suppliers will also be impacted by a 777X delay, particularly in Japan, where the 777 fuselage panels are made. In an interview at the Air Show, a senior Japanese industry executive, who requested anonymity to protect his relationship with Boeing, expressed great surprise at the news of the delay and said “it might cause us some problems in our factories.”

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The 777 had been for many years a cash cow for the Japanese industrial giants Kawasaki, Mitsubishi and Subaru. However, Boeing cut production from seven jets per month in 2016 to just 3.5 per month during the transition to the 777X.

The executive said Boeing’s Japanese suppliers “need a ramp-up of 777X as early as possible” to begin to restore that revenue — which makes the looming threat of a delayed entry into service very bad news that Boeing hasn’t communicated to its supply chain.

The bad 777X news in Paris follows earlier indications this month of a drop in demand for the airplane.

Greg Smith, Boeing’s chief financial officer and executive vice president for Enterprise Performance & Strategy, told a recent conference in New York that because of sparse orders for the smaller 777-8X version, Boeing is “looking at the timing and demand for the -8 to see if that still makes sense, and do we want to push that out?”

That statement may have been prompted by the fact that Emirates is renegotiating the terms of its 150 airplane order, possibly cutting some of the airplanes in favor of buying 787 Dreamliners, but certainly deferring some until later.

At the Aerospace Media Awards held in conjunction with the Paris Air Show, Seattle Times reporter Dominic Gates was honored Sunday for writing the year’s “Best In-depth Aviation Feature.” His March 17 story, “Flawed analysis, failed oversight: How Boeing, FAA certified the suspect 737 MAX flight control system,” gave the first detailed look into the approval process for the MCAS system implicated in the two fatal crashes of the Boeing jet.