Boeing's new 777X is finally expected to fly passengers next year. Here are the 5 coolest cabin features.

• Boeing showed off its 777X cabin at the Farnborough Airshow in July.
• Project leaders explained new ways Boeing has innovated the cabin, from lighting to bin space.
• There is a large focus on optimizing the premium section as demand for high-dollar seats booms.

It's seven years late and has racked up over $15 billion in charges, but Boeing's most important plane is expected to finally fly passengers in 2027.

Over a dozen airlines are waiting on the yet-to-be-certified Boeing 777X, the world's largest twin-engine widebody in production, packed with more than 400 seats and capable of flying up to 9,000 miles nonstop.

Boeing says the wider cabin, longer wings with folding wingtips, and giant General Electric engines create more seat room, open new routes, and provide a more efficient and comfortable flying environment compared with the planes it's replacing.

After years of delays, Boeing executives reiterated in a July earnings call that the larger 777-9 variant is still on track to enter service next year. German flag carrier Lufthansa is the launch customer.

The giant new jet has become increasingly important. Airlines have baked it into plans to capitalize on booming demand for premium travel, expand their long-haul networks, and replace aging widebodies that are more expensive to operate. And Boeing needs a win — and the money — after years of diminishing trust among customers and the public.

But the 777X is far behind schedule. Boeing initially planned to deliver the jet in 2020, but a string of quality-control and safety problems at the planemaker have increased regulator scrutiny and slowed certification. Some buyers — notably Emirates — have voiced frustration over the cost of keeping older jets flying while they wait, and have declined to take delivery of some of the earliest-built 777Xs.

Still, airlines have placed more than 560 orders collectively, worth billions of dollars, for the passenger 777X variants.

At the UK's Farnborough International Airshow in July, Business Insider experienced a mock-up of the 777X cabin and spoke with Boeing to learn more about what flyers can expect onboard, assuming the jet launches as intended next year.

"Boeing wanted to produce a cabin that would be distinctive, that would be unique, that would be something that an airline could say 'we have something different to offer,'" Boeing's managing director of product marketing, analysis, and competitive intelligence, Justin Hale, told the media. "We believe we've done that with the 777X."

From new lighting features and strategic door placement to optimize premium cabins, here are the coolest things we saw.

The 777X has the widest cabin in its class

While the double-decker Airbus A380 and Boeing 747 remain the largest and widest passenger planes in service, the 777X boasts more cabin space than its 777 predecessor and the competing Airbus A350.

Hale said engineers added a foot of cabin width compared with Airbus by making the sidewalls and insulation thinner. This means the 777X, which can seat 426 passengers in two classes, retains its 10 seats per row, but flyers get a little more wiggle room, with up to 18 inches of width.

"It's the only airplane in the market today that can seat 10-abreast comfortably in economy," Hale said.

In premium, more cabin real estate means airlines can get creative. In a January promotional video, Emirates teased a new business-class social space on its 777Xs.

The 777-8 strategically expands premium

With premium demand booming, Boeing has adjusted its 777-8, the shorter sister to the 777-9, to give airlines more flexibility in configuring their premium cabins. It can carry about 400 people across two classes.

Hale said the team optimized the jet by moving one of the exit doors — which must have a clear path to the aisle — farther aft to stretch the space at the front of the plane. That allows the premium section to remain one uninterrupted area, with the exit door and its required aisle space instead incorporated into the first row of the next section.

"Using that door conveniently, not as a cross aisle that's in the middle of that premium cabin, but rather it marks the end of a premium cabin at the start of perhaps a premium economy or [regular] economy class," he said.

This attention to premium space comes as airlines create more complex seats, which in turn complicates certification. For example, Lufthansa has been operating new 787s with empty business-class seats because the seats haven't been certified.

Hale said Boeing has tried to offer pre-certified catalog options to reduce certification delays, but airlines want their own distinctive business classes to compete.

Premium cabins can ditch overhead bins

In another effort to innovate the premium section, Boeing has stripped the cabin of its center overhead bins to create an arch. The premium cabin doesn't need as much bin storage, and this design makes the front of the plane feel taller and more spacious.

"Imagine a business class cabin, certainly, but also maybe an ultra-premium, first-class type of cabin," Hale said. "There are some phenomenal types of ultra-premium products that airlines are working on to put in their 777-9s when they go into service."

The economy section keeps the center bin space, essentially flipping the arch upside down into a V-shape. Hale said this "tricks the eyes into thinking that there's more width and space horizontally," rather than vertically, because that's what coach flyers often care about.

The 777X has customizable LED lighting

The 777X has a special LED system that allows airlines to customize lighting colors, intensity, and sequences for different phases of flight.

Boeing says the lighting schemes can help passengers get better rest, feel less jet-lagged, and more easily adjust their circadian rhythms.

An airline may use oranges and pinks to evoke a sunrise, or blues and purples to mimic nighttime. There's also a northern lights scene.

The 777X windows are bigger than Airbus'

Hale said the 777X has solved a few long-standing problems with aircraft windows.

First, he said the 777X will have the second-largest passenger windows in the industry, behind only the 787, and they will sit higher on the sidewall to give passengers a better view out. Earlier generations of widebody aircraft, he said, placed windows lower because designers assumed flyers would want to look down.

Hale also said the 777X will retain the dimmable-window design introduced on the 787 rather than use manual shades, in part because it gives passengers without a window seat a reference to the horizon.

"Our research has shown that when you're sitting in a middle seat, your ability to have a horizon reference, even peripherally, helps you feel better, especially 12, 14, or 16 hours into a flight," Hale said. "The dimmable windows are a way to cut the light without taking away that horizon."