General Electric is currently developing the largest turbofan engine ever to be used in commercial aviation. The GE9X is being made to power the Boeing 777X next generation widebody airliner, as the enormous engine will be installed on the world’s single largest twinjet to ever fly. Therefore, its test bed needs to be equally huge. That’s where the Boeing 747 comes in.

The colossal engine is being constructed using innovative manufacturing methods like 3D printing to make it not only the most powerful engine ever installed on a jetliner but also the most fuel-efficient. The GE9X will take commercial turbofan engine technology to the next level, to ensure that it is performing to the expectations set for it. The 747 is a perfect test bed.

The road to certification is a very long and arduous process for any aircraft and its major systems, specifically engines, and with the first deliveries of the 777x pushed back to 2027 from 2020. Boeing has been struggling with its latest widebody design for over half a decade, making it extremely urgent to push ahead with development across every part of the program.

The Boeing 747 is not only large enough to carry the engine but also flies the same profiles that would be expected of a 777X. It is similar in weight and handling characteristics, which makes it much simpler for the GE engine division to refine the design before it is installed on one of the precious, rare prototype 777X airframes!

The Biggest Jet For The Biggest Engine

GE Aerospace uses a modified Boeing 747-400 as a flying testbed because its four-engine configuration provides critical safety and redundancy, along with the necessary physical size and performance envelope to safely test the GE9X.

The GE9X has a massive fan diameter of 134 inches (3.4 meters), which is larger than the diameter of a Boeing 737 fuselage. The sheer size meant it could only be installed under the wing of the 747-400 as it has a larger main gear strut and bigger tires than earlier 747 models to provide enough ground clearance for safe takeoff and landing.

The 747 is a large, powerful aircraft that can reach a wide range of airspeeds and altitudes. This allows engineers to put the test engine through all required operational conditions, from low-altitude maneuvers to high-altitude and high-speed flight.

The 747’s existing engines help manage the significant asymmetric thrust from the powerful GE9X by using the three remaining CF6 engines, particularly the two production engines on the right wing, to keep the aircraft flying in a balanced and controlled manner.

When the experimental engine (the GE9X) is mounted on the inboard pylon of the left wing, the aircraft still has three other fully operational production engines (CF6s) to ensure safe operation. This means the test aircraft can fly safely even if the test engine needs to be shut down or fails during flight.

The GE9X In Dubai

The Boeing 777X was one of the most popular aircraft on display at the Dubai Airshow 2025, which just recently concluded. Among the many innovative technologies and highly anticipated features of the plane are its record-breaking power plants. The GE9X set a Guinness World Record when it was tested, producing 134,300 lb of thrust. The engines have also been optimized for fuel efficiency and exceptional durability, even in hot, harsh environments like the Middle East.

As the top customers of the 777X and owners of the largest widebody fleets in the world, Boeing has tailored its next-generation widebody for Gulf carriers since the program began. Cristina Seda-Hoelle, who heads up GE Aerospace’s GE9X engine program, made these remarks just before the airshow opened its doors:

“Dubai is really important for this program, as two-thirds of the sales of the aircraft and engine have occurred from Middle East customers. We’ve been using our time [before entry into service (EIS)] wisely. Continuing to test and iterate the design to ensure that when we launch this engine, it is as mature as possible for our customers.”

Of the 14 carriers that have ordered the 777X, none of them are from the United States’ “Big Three” of United, American, and Delta Air Lines. Of the 550 total orders, Emirates raised its share by 65 aircraft during the air show to exceed 200 in total as of now. All of that is to say that dust resilience will be an extremely important factor in the fleet performance and reliability when the 777X finally enters commercial service.

Test And Test Again

The GE9X is the most tested engine in the history of GE Aerospace. The engineers have extensively analyzed the engines not only to validate their durability, efficiency, and performance in real-world conditions but also to make improvements wherever possible in the design. Seda-Hoelle noted that the company has applied cutting-edge technologies with a “test early, test often” philosophy.

Since earlier this month, the GE9X has been undergoing dust ingestion testing with a series of 1,600 test cycles completed by November 15. GE9X program manager Karl Sheldon commented on the testing with the following statement:

“We’ve pushed this engine to the limits of what it might experience in the harshest conditions that we can imagine. Images of the engine looked good. 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.”

The United States Federal Aviation Administration certified the engine in 2024, marking a major milestone in the process to become the exclusive powerplant of the Boeing 777X. GE will be the sole engine supplier when the next-generation widebody enters production. The dust ingestion tests are designed to evaluate the impact of some of the most grueling flying conditions on the engine’s core, where the compressor, burner, and turbine are located.

The wear and tear on these crucial components significantly impacts any turbofan engine’s efficiency and performance. That not only means it has to burn more fuel to achieve the same amount of thrust, but also produces more carbon dioxide emissions and brings it to its next off-wing maintenance cycle ahead of schedule.

The Danger Of Dust In A Turbofan

Especially in the Middle East, the risk of ingesting a significant amount of dust is very high during takeoff, and during the first few thousand feet of altitude during the climb out from the airport. As the engine is operating during this critical phase of flight, it is pushed to nearly its maximum operating capacity. Flying at Full Throttle, the engines hit 1,000 degrees Celsius.

Flying at high altitude with hot-burning engines means dust can melt and infiltrate internal engine components. Once they work through the different stages of the jet engine, they can reach the high-pressure turbine downstream of the combustion chamber in the hottest part of the engine, which is especially vulnerable to Molten debris.

So far, the GE9X has passed every test the engineers can throw at it. Program Manager Sheldon remarked:

“That’s important, because the flying environment and mission will vary widely from customer to customer. Some people might drive their car at 4,000 RPM, but others might be driving at a completely different speed. There’s different wear and tear on the vehicle as a result.”

So far, the dust ingestion tests have been done on a static rig with engineers simulating the full flight envelope. That consists of a simulated takeoff followed by a climb to cruise and a landing. Using this special testing facility, engineers can simulate the volume, trajectory, and velocity of airborne debris encountered on a typical journey. The next step is to take it onto a real airplane.

GE is conducting 3,000 cycles of ground testing on the GE9X to support Extended Operations (ETOPS) approval, which is an extremely important certification for aircraft flying long-haul itineraries. The enormous size of the 777X and its industry-leading range will make it one of the most popular transoceanic and transcontinental aircraft in history. Its leading customers will be immediately putting it into service on just such routes when it is finally delivered.

GE’s Unique Jumbo Jets

GE Aerospace’s flying testbed is a highly modified Boeing 747-400, which serves as an airborne laboratory for testing new jet engines. This is the second 747 testbed GE has operated, replacing an older 747-100 in 2010. The current testbed is a Boeing 747-400 with the registration number N747GF.

Over its years of operation, GE’s 747 testbeds have been instrumental in the development and certification of numerous engines, including the GE90, GEnx, CFM LEAP, and the GE9X. N747GF was originally delivered to Japan Airlines in 1994 as a commercial passenger airliner before being acquired by GE in 2010. The aircraft is based at GE Aerospace’s Flight Test Operations (FTO) center located at the Victorville Airport in the Mojave Desert, California.

The testbed is primarily powered by three of its original CF6 engines. The fourth engine, located on the inboard pylon of the left wing, is replaced with the experimental engine being tested. The aircraft’s main deck, which once held hundreds of passenger seats, has been largely stripped and filled with racks of computers, data-acquisition systems, and workstations for a team of 15 to 20 flight-test engineers. The testbed will continue to be a vital asset for future engine programs, including the CFM RISE program, which is developing an « Open Fan » architecture aimed at significantly improving fuel efficiency.