WH002 (N779XX) handles autoland certification and ground-effect validation.
WH003 (N779XY) is responsible for GE9X engine integration, auxiliary power unit (APU), avionics checks, and flight-load measurement.
WH004 (N779XZ) is tasked with cabin systems testing including environmental controls, ETOPS certification requirements, noise validation, and reliability testing.
Distributing these roles across multiple airframes allows Boeing to run simultaneous test tracks while providing redundancy. This strategy proved valuable when structural cracks were found in the thrust-link of WH003 in August 2024—a problem that grounded the fleet but did not halt all progress thanks to multiple available aircraft. Boeing worked with GE to redesign and reinforce affected components without requiring an entire pylon redesign. By late 2024 regulators cleared the revised aircraft for resumed flights.
On January 16, 2025, WH003 resumed flight testing after repairs were verified. By April 2025 all four original prototypes had returned to active duty: WH001 and WH002 continued with control system tests while WH004 resumed cabin-level validation after a long hiatus. As reported by Air Data in May 2025, this overlapping workflow helped maintain momentum despite earlier disruptions.
In August 2025 Boeing introduced a fifth test aircraft: WH286 (N2007L). Unlike previous prototypes it is built to production standards with minimal instrumentation—intended for final electromagnetic interference (HIRF), lightning strike protection assessments, and airline-like cabin system validation. After completing these tests WH286 will be transferred to Singapore Airlines following retrofitting for commercial service. According to Aero World this marks a critical step toward demonstrating real-world operational readiness that cannot be achieved using more heavily customized prototypes.
Data from Flightradar24 shows that on August 5, 2025—the day of its maiden flight—WH286 flew over Washington state for more than two hours before joining the broader test campaign. This was also the first new-build Boeing 777-9 flight in nearly five years.
Historically Boeing has relied on large fleets during major certifications; nine aircraft supported original Triple Seven development in the early 1990s according to This Day in Aviation. That precedent saw extensive environmental trials ranging from desert heat to Alaskan cold prior to simultaneous FAA and European JAA approvals in April 1995.
Boeing’s current multi-airframe strategy again facilitates wide-ranging environmental validation—including tropical hot-weather flights such as February’s journey by WH002 to Curaçao covered by Simple Flying—and ensures robust regulatory oversight at every stage leading up to delivery configuration checks with WH286.
Delays from structural issues interrupted certification progress but recent advances have brought renewed optimism among airlines awaiting deliveries—particularly major customers like Emirates, Qatar Airways, Lufthansa, Cathay Pacific and Singapore Airlines who have ordered hundreds of units according to Business Insider. Singapore Airlines’ own aircraft (WH286) is expected as Boeing’s first customer delivery once all requirements are met.
Boeing aims for final certification between late 2025 and early 2026 followed by initial handovers that year—a timeline adjustment driven largely by technical challenges encountered during multi-airframe testing but potentially setting a benchmark for future high-complexity programs such as the proposed New Midsize Airplane ("797").
The use of five specialized aircraft enables parallel testing streams across aerodynamic behavior, propulsion systems integration, advanced safety features like folding wingtips—and full-scale operational scenarios reflecting airline needs—all contributing toward safer entry into service for one of aviation’s most anticipated widebody jets.
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