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Boeing is poised to conduct a functional check flight on the third 777-9 test aircraft, marking a return to flight for the stalled certification program after a five-month grounding caused by the failure of engine thrust links.
The flight, which is expected as early as Jan. 15, follows the replacement of the thrust link components on the four primary test aircraft in the 777X certification program. Delays to the effort caused by the component failure and compounded by a seven-week labor strike in late 2024 have already forced Boeing to push initial deliveries back to 2026.
Boeing declines to comment about the upcoming flight, which also follows a period of rework on the aircraft’s thrust reverser assembly. The shakedown mission is expected to pave the way for the full resumption of the certification program, which had been underway for around five weeks when the thrust link failure brought proceedings to a halt in mid-August.
The third test aircraft, WH003, has not flown since Sept. 8, 2024, when it was ferried back to Seattle from Kona, Hawaii, where it had been conducting flight tests when the failure was first detected. WH003, which originally joined the program in August 2020, is the lead aircraft in the initial certification effort, which followed the granting of FAA type inspection authorization in July 2024.
At the time of the thrust link failure, WH003 was believed to be engaged in propulsion testing with the production standard GE Aerospace GE9X engine with an updated combustor liner and the latest load of engine control software. In the initial flight test program, WH003 was used primarily to evaluate flight loads and performance of the auxiliary power unit, as well as avionics and engines.
The prototype 777-9, WH001, which first flew in January 2020, last flew on Aug 12, 2024. The aircraft, which is also expected to rejoin the program within weeks, previously took the lead in stability and control testing, as well as evaluations of high- and low-speed aerodynamics. It has also been used for avionics, flight control systems and brake tests.
The second aircraft, WH002, joined the test fleet in April 2020 and last few on Aug. 9, 2024. This aircraft has been used mainly for autoland system work as well as ground effects testing. A fourth aircraft, WH004, which last flew in November 2021, incorporates a production-representative cabin configuration, and will ultimately finish its test role with a phase of extended twin-engine operations and airline-like functionality and reliability operations testing.
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