Boeing’s biggest year yet for the 777X, final assembly of the company’s future long range flagship, is starting on schedule for everything but the engines, flight testing of which has been delayed by issues with the GE9X and General Electric’s flying testbed.

The GE9X slip marks the first known major schedule challenge for the 777X program which to-date has progressed smoothly and to plan since the Boeing board approved its launch in 2012. The successful development of the 105,000 lb.-rated GE9X, which is the exclusive engine for the stretched Boeing twinjet, is critical to the program and has remained on track up to this point.

However GE says the slip does not jeopardize the schedule for the overall engine certification program or the first flight of the 777X which is targeted for early 2019. “We are working with Boeing to protect the schedule,” says the engine maker. GE, which originally hoped to fly the GE9X for the first time at the end of December, still aims to clinch certification in early 2019 but says it is yet to determine exactly when flight tests will begin.

The GE9X issue is related to the lever arms which actuate the rows of variable stator vanes (VSVs) that modulate flow through the 11-stage high pressure compressor (HPC). “The GE9X team had a test finding in the HPC during a demonstrator engine test late last year. After analyzing the engine data, the team determined that the lever arms for the VSVs need to be changed,” GE says. The company adds that while the configuration will be changed for the production engine a decision is still pending on whether flight tests can at least get underway with the existing VSVs arrangement.

The GE9X on the flying testbed is the fourth engine in the test program. The VSV arm issue came to light during runs of the second engine which was used to demonstrate the performance conditions which will be required to pass the official FAA 150-hour block test later in 2018. During this intensive test, the engine was run at triple red-line conditions (maximum fan speed, maximum core speed and maximum exhaust gas temperature) to gauge operational limits.

However, with Boeing and GE seemingly confident that this first schedule hiccup will not impact the timing of first flight of the 777-9 in about a year from now, the program continues on plan with production underway of the four airframes and more than 30 test laboratories up and running in Seattle, Washington.

As assembly begins Boeing is in the final stages of defining the last elements of the 777-9, the first and largest variant of the 777X to be developed. Engineering design release, which passed the 90% milestone at the end of 2017, has now reached 93% and is expected to be completed over the next few months. Meanwhile more than 30 ground test labs, most of them in Seattle, are up and running or preparing to begin testing, including the integrated systems and avionics facility which is so close to the complete configuration of the real 777-9 that it is dubbed the Airplane Zero Lab. Others in the suite of ground test facilities include the eCab lab, which went online in January, where pilots evaluate interaction with the updated 777X flight deck and its new features such as the wing fold controls.

Major structural elements of the 777-9 static test unit, the first complete 777X airframe, are coming together at Everett where it will enter final assembly in the second quarter. Assembly of the initial complete aircraft will take place at a temporary location in Building 40-23 between the current 747-8 and 777 assembly lines. Dubbed the low rate initial production (LRIP) line, the site will used to prove out the production process on the new 777 variant without disrupting the adjacent 777-300ER.

Assembly of the first production wing spar for the first flight test 777-9 began in October and production of the rest of the airframe “is progressing well,” Boeing says. Spar fabrication for the second and third flight test aircraft is also underway in the $1 billion composite wing center (CWC) at Everett. In all six 777-9 airframes, four of them for flight testing and one each for static and fatigue tests, will be assembled in 2018. Roll out of the first 777-9X is due in late 2018 with the first flight expected around February 2019. All four test aircraft are scheduled to be in the flight program.