John Walton, CNN

The world’s longest flight: nonstop, 20 hours, as you recline in your wide armchair and decide whether you want to relax with the very best Champagne, enjoy a chef-designed meal with a traveling companion seated opposite, or get the crew to make your sumptuously soft bed with fresh linens.

That’s what’s on offer for the six first-class passengers on board Qantas’ Project Sunrise direct flights to Sydney from London and New York starting three years from now, and they can expect to pay the best part of five figures for it.

What about the 140 economy class passengers who will be at the back of the 12 Airbus A350-1000s that the airline has ordered to work on the service?

Qantas isn’t telling. “We don’t have any updates at the moment but we are eager to keep you updated, and will share more when we have it,” a spokesperson told us.

We do know, though, that Qantas is already planning a Wellbeing Zone, which looks to be an area around one of the galley kitchens where you can stretch, maybe do some yoga poses, and possibly just stand around for a while.

And, of course, Qantas will work hard at having a great selection of movies and TV shows for you to enjoy on big new inflight entertainment screens, as well as food and beverages that it’ll design especially for your wellbeing on longer flights.

But that’s likely it.

Ian Petchenik, host of the AvTalk aviation podcast, tells CNN that “while a lot of attention has been paid to Qantas’ first class for Project Sunrise, I think the real differentiator for passengers in the back of the aircraft is going to be the soft product.

“You can only improve nine-abreast economy seating so much, so finding ways to make a 20-hour flight in one of those seats palatable is going to come down to what else Qantas can offer those passengers.”

I’m a specialist aviation journalist with more than a decade going in-depth with all kinds of people at airlines, airplane manufacturers, designers, and seatmakers to figure out how every inch of the plane is used. And since Qantas isn’t talking, here are my professional deductions about what’s likely to be on offer on board.

First off, there isn’t much likelihood of anything really revolutionary. The three years to 2025 aren’t a long time in aviation, especially when it comes to seats. Unless Qantas is planning some sort of big bunk reveal — which would require a massive amount of safety certification work — it seems pretty certain that economy passengers will just be in normal seats.

Knees and shins

Going back to first principles, comfort levels in economy class seats are mostly based on seat style, pitch and width.

In terms of seat style, Qantas can be expected to pick up the very best economy class seats on the market from the top design and engineering firms, like Recaro or Collins Aerospace.

These are called fully featured seats, with comfortable engineered seat foams covered by special fabrics, a substantial amount of recline, a substantial headrest, underseat footrest, and in Qantas’ case a small foot hammock.

In recent years, designers and engineers have worked hard on the backs and bases of airplane seats so that they give enough space to the person sitting behind — particularly for their knees and shins.

They’ve figured out how to make the cushioned bottom of the chair, known as the seat pan, articulate when reclined, changing the pressure points on the occupant’s body as they lean back.

Qantas’ Boeing 787-9 Dreamliners, which launched in 2016, used a customized version of German manufacturer Recaro’s CL3710 seat.

The CL3710 dates back to 2013, and Recaro has been making updates each year, but it wouldn’t be surprising if it was working on a special version for Qantas.

There might even be a brand new seat — from Recaro or someone else — with even more comfort. That could well be ready for Qantas to start flying in late 2025.

Extra legroom

The second factor in comfort is pitch, which measures the point on one seat to the point on the same seat immediately in front of it, so it’s not quite total legroom because it includes an inch or two of seatback structure.

Qantas has promised that its economy class seats on board will offer 33 inches (84 centimeters) of pitch.

That’s one inch more than the 2016 Dreamliner seats, and by 2025 I’d expect the seat engineering to have narrowed the seat structure by up to an inch to offer more knee space.

It wouldn’t be a surprise if Qantas offered extra-legroom sections too, which might stretch to 35 or 36 inches, along the lines of United’s Economy Plus or Delta’s Comfort Plus — not premium economy, but just normal economy seats with more legroom.

What about width?

There’s either great news or terrible news ahead for passengers, depending on how many seats Qantas puts in each row of the A350.

The big twin-aisle plane can either hold nine seats per row, which has been the standard that full-service airlines like Qantas, Delta and Singapore Airlines have offered, or 10 seats per row, which has largely been aboard ultra-low-cost and leisure carriers like France’s Air Caraïbes and French Bee.

Width-wise, the A350 is one of the most comfortable economy class options in the air at nine-across with seats over 18 inches wide. At 10-across, it’s one of the least comfortable, with seats barely scraping 17 inches and super-narrow aisles too.

You might imagine — and Qantas’ published cutaway certainly shows — that a full-service airline like Australia’s flag carrier would naturally go for the nine-across configuration.

But Airbus has been hatching a quiet plan to carve out an inch or two of extra space by slimming down the cabin sidewalls. That’s led some full-service airlines, including Abu Dhabi-based Etihad, to plan to install 10-across seating on some future A350s.

Nonstop vs. stopover

Qantas says that it plans to install 140 economy class seats on its A350. That would be 14 rows of 10, but that number doesn’t divide neatly into nine, even if you try to add some extra seats on the sides or in the middle.

It would still be surprising to see Qantas do that, especially for these super-long flights. But the airline installed seats almost as narrow on its Dreamliner seats that fly nonstop London-Perth for nearly as long, so watch this space for details.

At the end of the day, every inch matters when it comes to economy class comfort. Many passengers — me included — wince at the idea of a 20-hour-plus flight, even in business class.

I’ve done something almost as long in business class, on Singapore Airlines’ nonstop from Newark to Singapore about 10 years ago, but it wasn’t much fun, even with the ability to go from movie to sleeping and back again.

Whenever we end up talking about this, people always bring up the other option, a stretch halfway from New York to Sydney in Los Angeles or San Francisco, or in any of a dozen top-notch airports in Asia between Sydney and London.

But people have always winced at spending longer in a seat: first at the idea of a single-hop Kangaroo Route flight, then at the idea of a flight lasting 12, 14 or 16 hours.

Before the pandemic, there were dozens of flights longer than that, with regular economy class seats down the back, and people seemed willing to sit in them.

The question is just how much of a difference that extra three or four hours over the London-Perth Qantas 787 Dreamliner flight will make to passengers — and, crucially, to their perceptions.

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