For most of its 777X testing, Boeing has operated four prototypes. These aircraft are WH001 (N779XW), WH002 (N779XX), WH003 (N77XY) and WH004 (N779XZ). However, in August 2025, a fifth test aircraft entered testing: WH286 (N2007L). This aircraft is a production-standard Boeing 777-9. That means it lacks the complex flight-test instrumentation that can be found on the other test prototypes. That is because WH286 has been designed to be as close as possible to an airline-ready configuration. The limited instrumentation also allows for testing of electromagnetic interference, lightning strike safety, and validating operations in a realistic operating environment. As a result, it is expected that Boeing will transfer this aircraft into Singapore Airlines’ ownership once the 777X has received certification.

In this article, learn more about the 777X test variants and how each of them has been used to carry out essential testing to get this much-delayed aircraft into the skies. We then finish with the testing that Boeing and General Electric have been able to do, which doesn’t require the use of one of the five exceptionally rare prototypes.

The Role Of Each 777X Prototype

Credit: Wikimedia Commons

Each of the 777X prototypes carries out a different role in the testing program, hence the need to build five of them. The first prototype, WH001, has been testing the jet’s stability, flutter, avionics, brakes, aerodynamics and control systems. Much of the flight testing has been conducted at low speeds. Meanwhile, WH002’s testing has been on ground-effect and obtaining autoland certification. Further testing has been aimed towards flight-control envelope expansion.

WH003’s primary task has been to test GE9X engine integration. It has also had a role in avionics testing and flight-load measurement. WH004’s testing has concentrated on real-world operations, looking at cabin systems, environmental control, noise, and reliability testing. It is also this jet that has led to endeavors to achieve ETOPS testing. Finally, WH286 gets as close as a prototype can to the production variant, allowing for testing that isn’t possible while carrying extensive testing equipment. It is yet to have seats and side walls installed. Throughout this testing, these jets have accumulated over 4,000 flight hours across over 1,400 flights.

The table below shows the service history of the 777X prototypes up to August 16, 2025:

Beyond ensuring that testing can be done more efficiently and allowing prototypes to be designed with specific testing in mind, having multiple prototypes also allows tests to continue when things go wrong. In August 2024, structural cracks in WH003’s thrust-link grounded it. Although the issue eventually grounded the other test aircraft, using multiple airframes allowed Boeing to incorporate corrective measures while avoiding a total campaign shutdown.

Related

Boeing Will Restart 777X Certification Flight Tests

Boeing last operated a 777-9 flight in September 2024, when it ferried N779XY from Hawaii to the continental United States.

The New Prototype Takes To The Skies

Credit: Wikimedia Commons

In August 2025, the fifth Boeing 777X prototype took to the skies. It conducted a 2-hour, 27-minute test flight that assessed the production standard Boeing 777-9’s handling and performance. It successfully took off from Paine Field near Boeing’s Everett plant, and the flight was the first Boeing 777-9 flight in five years. The whole affair was watched by Boeing employees standing on the Future of Flight museum’s balcony and surrounding grassy areas, and they cheered while the jet, in an all-white livery, taxied, unfolded its wings, made a first practice takeoff run (to test the brakes), and eventually took off.

While the prototype was built to test for electromagnetic interference and for safety after a lightning strike, the first flight was intended to ensure all flight systems were working properly and that the jet was handling as expected. All of these tests had already been conducted on the ground. Yet, this was much more than a simple takeoff and landing. In the 147-minute-long flight, the aircraft reached 39,000 feet and had a cruising speed of Mach 0.84. The flight also had important marketing value for the manufacturer, showing that the 777X is moving in the right direction to receive certification soon.

Ted Grady, chief pilot of the Boeing 777-9, was behind the controls. He told The Seattle Times: “It really was a pretty smooth flight. You could tell that the team had the airplane in excellent condition.” After one further test flight, the jet headed to Arizona to conduct the intended lightning testing, ensuring the jet could operate safely in electric storms.

N779XW At The Dubai Airshow

Credit: Wikimedia Commons

One prototype, N779XW, made a noteworthy appearance at the 2025 edition of the Dubai Air Show, which began on November 17. The appearance was an important opportunity for Boeing to demonstrate to the Gulf Carriers, the largest 777X customers, that the enormous aircraft would soon be in their hands. Dr Brendan Nelson, the President of Boeing Global, commented from Dubai on November 6, 2025, “[The] Dubai Airshow is an opportunity to celebrate these achievements.”

FlightAware data shows that the aircraft conducted a series of short demonstration flights at the airshow before traveling back to King County International Airport – Boeing Field. This journey took 16 hours and 2 minutes with an actual distance of 8,616 miles.

The successful demonstration wasn’t the only reason for Boeing to celebrate at the Dubai Air Show. Emirates also placed an order for a further 65 777Xs worth a total of $38 billion, according to list prices. The order also has the option for Emirates to convert to 777-8s or -10s. Emirates could take this option if they see the 777X operating well in a commercial environment after its certification. HH Sheikh Ahmed bin Saeed Al Maktoum, Chairman and Chief Executive, Emirates Airline and Group, said: “Emirates is already the world’s largest Boeing 777 operator and we are expanding our commitment to the programme today with additional orders worth US$ 38 billion for 65 Boeing 777-9s, and 130 GE9X engines. This is a long-term commitment and testament to our partnership with Boeing and GE, and to US aerospace.”

Related

As It Happened: Dubai Airshow 2025

Keep up with the latest from on the ground at the 2025 edition of the Dubai Airshow!

The Storied Past Of Boeing’s Former Prototypes

Credit: Wikimedia Commons

Manufacturers’ prototypes don’t go to the scrapyard once they outlast their testing use, but enter the market. One example is WA001 (registered N7771), the first Boeing 777-200 to take flight on June 12, 1994. This flight took almost four hours, with the aircraft reaching an altitude of 19,000 feet (5,791 meters) and was observed by a Northrop T-38A Talon chase plane. Risky tests conducted mid-flight included shutting down and restarting one engine.

Once the Boeing 777-200 entered commercial service, Cathay Pacific purchased N7771, configuring it as a 777-267. The carrier also opted to replace the Pratt & Whitney PW4074 two-spool high-bypass-ratio turbofan engines with Rolls-Royce RB211 Trent 884B-17. These engines offered a weight reduction of 7,500 pounds (3,400 kilograms), allowing for more efficient operations. Newly registered B-HNL, the aircraft was delivered to Cathay Pacific on December 6, 2000.

Cathay Pacific operated the aircraft for almost 18 years before retiring it to a storage facility at Xiamen Gaoqi International Airport (XMN), Xiamen, Fujian Province, People’s Republic of China. It is now on display at the Pima Air and Space Museum, Tucson, Arizona.

Prototypes Aren’t The Only Way To Test 777Xs

Credit: Wikimedia Commons

With only five 777X prototypes available, they are exceedingly rare. Boeing will only use them for testing that absolutely requires a 777X testbed. An example of testing that won’t require the prototypes to take to the skies is the General Electric GE9X, built to power the aircraft. The Boeing 747-400 is an ideal testbed for General Electric, as its four engines mean that it offers plenty of redundancy should anything go wrong. The manufacturer could install GE9X’s on its 747 testbed for dust resilience testing.

Yet, it isn’t as simple as replacing a 747 engine with a GE9X. The enormous engine has a fan diameter of 134 inches (3.4 meters), which is more than the fuselage of a Boeing 737. The size and weight would need a larger main landing gear strut and tires to ensure the aircraft has enough ground clearance for takeoff and landing. The additional strain placed on the wing will also need to be taken into account.

Using a 747 for testing may be necessary due to the vast amount of testing that needs to be done before the GE9X can fly commercially. The dust ingestion experimentation alone has required 1,600 test cycles. They are necessary because of the highly dusty environment in the Middle East, where the largest 777X customers are based. GE9X program manager Karl Sheldon said in a statement: “Its core looks excellent, and all components are functioning as expected. These dust ingestion tests aren’t even part of any certification effort. We’ve now put this engine through more testing than any engine in our history prior to entry into service.”