I toured an experimental Boeing 777X aircraft, which the planemaker is using to certify the new $442 million widebody. See inside.

The aircraft was first announced in 2013 and has undergone production developments and challenges for over a decade.

Unlike the Airbus A350, which was a completely new design, Boeing's next-generation 777X builds off the successful track record of its classic 777 planes, particularly the historically popular 777-300ER. 

The latter proved to be one of Boeing's best-selling widebodies, with nearly 900 aircraft sold. 

The smaller 777-8 variant, which has been ordered by carriers like Emirates, has a longer range. It intends to fill the niche of longer-haul routes with less demand. 

The concept is similar to Boeing's successful line of 787 Dreamliners, which come in three sizes: small, medium, and large, all with varying range capabilities. 

According to GE, the engines are the biggest ever built in the world and can produce some 100,000 pounds of thrust. To give you a visual, the entire body of a Boeing 737 can fit inside the GE9X engine. 

GE first tested the innovative powerplant on a Boeing 747 test jet during a flight over the Mojave Desert in 2018.

The 777X has a wingspan stretching 235 feet and five inches with the wingtips deployed — which is 23 feet longer than older 777 variants.

Airports are designed with specific specs for everything from the width of the runways and taxiways to the gate ramp space, according to the Federal Aviation Administration. 

The above picture shows the space needed for an Air New Zealand Boeing 777 compared to a Lufthansa Airbus A340. 

When the wingtips are retracted, the wingspan is about 212 feet — the same as the classic 777. 

Without the folding wingtips, it's likely airlines and airports would be put off by the 777X due to the time and money associated with accommodating the longer wingspan.

A flight test pilot told BI in June 2022 at the Farnborough Airshow in England, the first time I toured the jet, that the wingtips lock in place in flight and only fold once the aircraft reaches the ground and slows to about 50 knots — meaning there is no risk of the wingtips retracting during a go-around.

"We have a whole slew of alerts that make sure the wingtips are extended prior to takeoff," he said. "It's part of our before-takeoff checklist, which is electronic."

Each plane has its own focus, testing a spectrum of technologies like auto-land, environmentally-friendly materials, low-speed performance, and extended twin-engine range operations.

These tests help Boeing demonstrate the 777X's safety and operating extremes to federal regulators responsible for certifying the jet.

A Boeing engineer told BI that the flights are primarily over the US, but a few are international to cover certain high-altitude tests.

The media got a rare look at the skeleton of the jet, which had its flight control systems and wiring exposed.

Flight test engineers conduct consecutive tests in one flight for efficiency, and there are typically anywhere from 10 to 20 people onboard, an employee told BI.

Higher-risk test flights will host fewer employees.

"If the type of testing is kind of difficult on the body, we won't fly very long," an engineer told BI during a tour of the jet at the Paris Airshow in June 2023. "If it's fuel mileage testing, it's clearly going to be longer."

The wiring — which is strewn throughout the entire plane — collects real-time data for the engineers to evaluate to ensure the plane performs as expected.

Engineers use the barrels to move water back and forth to "hold the aircraft's center of gravity for longer," allowing it to be tested under a range of different flight conditions, a Boeing engineer told BI.

According to Boeing, its windows are 29% bigger than those on the A350 and are placed higher on the fuselage to give passengers a better view and make the cabin feel bigger.

These tests are all done in various weather systems, too, including storms and rough turbulence.

An engineer told BI that the team flew on the 777X to get to the airshow, starting in Seattle with a fuel stop in Hawaii.

The engineer explained the seats don't feature anything special, joking that the team has testing data as their inflight entertainment.

"It [the 777X] is fairly comfortable," he said. "We can get up as much as we want. We'll stand at the table and eat. It's just a fun way to travel, especially for a really long-haul flight from the US to India."

Boeing's regional director of cabin marketing, Brenna Wynhof, showed the media the two different architectural cabin options, including "A" and "B."

The difference is in the curvature of the ceiling panels.

Wynhof said the arch of the ceiling panel from A is flipped 180 degrees to create the B ceiling architecture, explaining the former option is best for business and first class while the latter is best for economy cabins.

"Both of these can exist on the same airplane, with A in premium cabins and B in premium economy and economy," she told BI.

Wynhof explained the lighting is manipulated thanks to the different gradients Boeing can control

"The cotton candy sky is the best part of the sunset, and we can achieve the exact same gradient in the 777X because now we can intentionally eliminate the bin face color so the light can gracefully sweep across the cabin," she explained, noting the scene ends on a twilight sky.