Boeing took a significant step forward in its 777X certification program by reactivating its fourth test aircraft, known as WH0004 and registered as N779XZ, on April 13, 2025. The widebody jet's transponder was active under the callsign ‘BOE777’ for approximately an hour and a half at Seattle Paine Field International Airport (PAE), signaling a renewed push in the crucial testing phase.

This reactivation marks a turning point for WH0004, which had been parked at Paine Field since its last flight from King County International Airport (BFI) in November 2021. Its return to operational status underscores Boeing's commitment to overcoming earlier hurdles that had temporarily stalled the 777X certification process.

The other three 777-9 test airframes – WH001 (N779XW), WH002 (N779XX), and WH003 (N779XY) – have been actively involved in flight testing since January 2025. These aircraft resumed regular operations after Boeing addressed technical issues, notably problems with the engine thrust links, which are structural components critical for connecting the engine to the aircraft's frame. WH003 was the first to experience cracks in these links, leading to a suspension of flight tests until the beginning of this year. Prior to these issues, the certification program had reached the Type Inspection Authorisation stage, indicating substantial progress.

Flight records reveal a flurry of activity among the currently flying test aircraft. WH001 completed its initial post-grounding flight on January 23, 2025, traveling from Paine Field to Moses Lake Grant County International Airport (MWH). WH002 resumed its flight schedule on February 5, marking its first journey since August 2024. WH003 was the first to return to the skies on January 16, completing a flight that began and ended at Boeing Field (BFI). Notably, all three aircraft conducted their most recent test flights just two days prior to the reactivation of WH0004, on April 11, 2025.

These positive developments in the 777X program occur against a backdrop of changes at Boeing’s Everett production facility, where the company assembles its widebody aircraft. Following the cessation of 747-8 production in January 2023, Boeing had announced plans to introduce a fourth 737 MAX production line at the site.

However, the Federal Aviation Administration (FAA) has since prohibited any expansion of production or the addition of new lines until Boeing demonstrates significant improvements in its aircraft quality control processes, a stance supported by the Department of Transportation.

Despite these broader production constraints, the 777X certification efforts appear to be gaining traction. During the Bank of America Global Industrials Conference on March 19, 2025, Boeing’s Executive Vice President and Chief Financial Officer, Brian West, announced that the FAA had approved the second phase of 777-9 flight testing. This crucial phase focuses on evaluating the aircraft's aerodynamics, braking systems, and engine performance. As of mid-March, the 777-9 had accumulated an impressive 3,700 flight test hours.

Further reinforcing the company's commitment to its development timelines, Boeing CEO Kelly Ortberg stated during the company’s Q4 2024 earnings call on January 28, 2025, that the certification schedules for the 777X, as well as the 737 MAX 7 and 737 MAX 10, remain on track. Boeing maintains its goal of certifying all three aircraft models in 2025, with the first 777-9 slated for delivery to launch customer Lufthansa (LH). The company is scheduled to release its Q1 2025 financial results on April 23, having already reported the delivery of 130 commercial aircraft during the first quarter.

The Boeing 777X represents the newest iteration of the highly successful Boeing 777 family, which holds the distinction of being the most-produced widebody aircraft globally and the largest commercial plane currently in production. Boeing is developing three variants of the 777X: the 777-8, the 777-8F (freighter), and the 777-9, all designed with a focus on enhancing passenger comfort and operational efficiency. To date, the 777X program has garnered 379 orders from 9 different customers, excluding the four test aircraft built specifically for the development and certification process. 

While the 777-9 variant has seen significant interest, the 777-8 passenger version has attracted fewer orders, with Emirates (EK) and Etihad Airways (EY) currently listed as the primary customers. Notably, Air India (AI) has committed to purchasing 10 of the 777-9 variant, highlighting the aircraft's appeal in key international markets. The reactivation of the fourth test aircraft signals a renewed intensity in Boeing's efforts to bring this next-generation widebody jet to market.