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Boeing Will Restart 777X Certification Flight Tests

Boeing could restart the flight test program for the 777X soon after grounding its four testing airframes due to an issue with the type’s thrust links in August 2024.

According to a report by AviationWeek, Boeing is set to resume flight testing of the 777X , with the first flight potentially coming as soon as January 15 (at the time of publishing, the flight still has not happened). The manufacturer suspended the campaign after it found severed thrust links on all four test aircraft in August 2024.

None of the four 777-9 test aircraft have flown since September 2024. Boeing's last 777-9 flight was on September 8, 2024, when it ferried the N779XY, also known as WH003, from Kona International Airport (KOA) to King County International Airport (BFI). Before that flight, the airframe's last operation was on August 15, 2024, when it flew for five hours and 31 minutes near Hawaii, departing from Kona and landing back at the same airport.

N779XX (WH002) and N779XW’s (WH001) last outings were on August 9, 2024, and August 12, 2024, respectively, while N779XZ (WH004) has not operated a flight since November 2021. The latter aircraft’s transponder was briefly online on April 4, 2024, according to Flightradar24's records.

In August, Boeing told Simple Flying that the severed thrust links were discovered during scheduled maintenance. The company replaced the part and had been capturing any learnings from the component, and that it would resume flight tests when ready, the plane maker's spokesperson added. The Air Current was the first to report the development.

However, Boeing's representative emphasized at the time that no near-term flight tests were planned on the other airframes – the first aircraft with the severed thrust links was N779XY (WH003) – that had scheduled maintenance and “layup activities.”

Terrific aircraft...Shortly after N779XY (WH003) returned to the continental United States from Hawaii, Brian West, the chief financial officer (CFO) and executive vice president of finance of Boeing, spoke at the Morgan Stanley Laguna Conference on September 13, 2024. The event started several hours after the manufacturer’s 33,000 machinists across several states kicked off their strike that would last until November 2024.

West clarified that Boeing had discovered damage to one of the thrust links on the flight test aircraft. In response, the plane maker immediately paused the flight test program, and subsequently, its engineers began to determine the root cause and potential corrective action to get the 777-9 test fleet back into the air.

Progressing through certification...Before the thrust link issue that grounded the 777X test flight fleet for months, Boeing had continued progressing with the type's certification. In July 2024, after securing the Type Inspection Authorization (TIA) for the 777-9, it began flight tests with the Federal Aviation Administration’s (FAA) representatives onboard.

TIA is “used to authorize official conformity, airworthiness inspections, and flight tests necessary to fulfill certain requirements for Type Certificate (TC), Supplemental Type Certificate (STC), amended TC, and amended STC certification,” according to the FAA.

For the 777X, Boeing will amend the 777’s TC to include the 777-9, “a derivative of the Boeing Model 777 airplane currently approved” by the FAA, per a document published by the regulator in August 2024. Before the thrust link issue, Boeing had anticipated that the 777-9 would enter service sometime in 2025.