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How Many Boeing 777X Prototypes Were Built?

How Many Boeing 777X Prototypes Were Built?
Boeing’s 777X program has relied on a dedicated fleet of prototypes to conduct its extensive and often delayed testing campaign. Throughout the majority of its flight testing, Boeing has operated four primary prototypes: WH001 (N779XW), WH002 (N779XX), WH003 (N779XY), and WH004 (N779XZ). In August 2025, a fifth aircraft, WH286 (N2007L), joined the test program. Unlike the earlier prototypes, WH286 is a production-standard Boeing 777-9, constructed to closely mirror the configuration that airlines will ultimately receive. This aircraft is notably devoid of the complex flight-test instrumentation present on the other prototypes, enabling Boeing to perform tests in a more realistic operational environment, including assessments of electromagnetic interference and lightning strike safety. Upon completion of certification, WH286 is expected to be delivered to Singapore Airlines.
Beyond these five specialized test aircraft, Boeing has significantly expanded its 777X prototype fleet. As of August 12, 2025, the company has built a total of 26 prototypes. This larger fleet reflects both the scale of testing required and Boeing’s efforts to prepare for commercial deliveries. Emirates, one of the program’s largest customers, has placed a substantial order for 65 additional 777X aircraft. However, the program has faced challenges, including ongoing certification delays that have resulted in the removal of 33 orders from Boeing’s backlog. Despite these setbacks, Boeing remains optimistic, targeting the 777X’s entry into commercial service by 2027.
The Role of Each 777X Prototype
Each of the five main test aircraft has fulfilled a distinct role in the certification process. WH001 has focused on stability, flutter, avionics, brakes, aerodynamics, and control systems, with much of its testing conducted at low speeds. WH002 has been dedicated to ground-effect testing, autoland certification, and expanding the flight-control envelope. WH003 has primarily supported GE9X engine integration, as well as avionics and flight-load measurement. WH004 has concentrated on real-world operations, including cabin systems, environmental controls, noise, reliability, and ETOPS testing. The newest addition, WH286, as a near-production aircraft, facilitates operational testing without the constraints imposed by heavy instrumentation, although it has yet to be fully fitted with seats and sidewalls.
Collectively, these prototypes have accumulated over 4,000 flight hours across more than 1,400 flights. The use of multiple airframes has allowed Boeing to maintain testing momentum even when technical issues arise. For instance, in August 2024, structural cracks in WH003’s thrust-link grounded the aircraft and eventually affected others. Nevertheless, the availability of several prototypes enabled Boeing to implement corrective measures without halting the entire test campaign.
Looking Ahead
As Boeing continues to expand its prototype fleet and address certification challenges, the company remains committed to bringing the 777X to market. With 26 prototypes built and major customers such as Emirates awaiting delivery, the 777X is positioned to become a significant player in the next generation of long-haul aviation, contingent on successful certification and entry into service, now targeted for 2027.

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