I got this email some time back from Dale in Melbourne, Australia, and I've been meaning to address this very subject here in the blog:

Well Dale, I’m going to clarify those questions for you right now.

As you've probably heard, when we designed the 787, one of the things we wanted to do was provide a superior environment for the passenger. Everything from the comfort of the seats you sit in, to the refreshing atmosphere inside the cabin, the lighting, the open architecture, the whole scheme of things.

So a big part of our efforts focused on actually shaping the airplane in a way that would enhance the cabin interior. And we chose to go with what is often referred to as a "double-bubble" fuselage.

What that means is a double circle. It allows us to have the lower section of the airplane shaped the right size for cargo, and allows us to situate the shape of the upper section so that the widest part of the passenger cabin is higher up from the floor. This allows for a straighter sidewall, more comfort around the window seats, and a wider cabin overall.

In the image above, you can see that the cross section we chose for the Dreamliner allows us to provide a 9-abreast configuration - with the same kind of comfort levels you find in economy class in today's airplanes such as in the 747 and the A330/A340. Basically, the very same triple seats used in the 747 could be used in a 9-abreast configuration in the 787.

But the beauty of the 787 is the built-in flexibility for airlines for the different kinds of markets they serve. Our customers will have the option in the Dreamliner of providing a premium economy arrangement at 8-abreast. This allows for the largest seat available - bigger than you'd find today in economy - a 19 inch seat bottom.

Now here's the issue. When it comes to comparing the 787 to the Airbus alternative, there's been some confusion. Should this be an 8-abreast to 8-abreast comparison? Or a 9-abreast to 9-abreast?

I'd say neither.

Because Airbus does not have an acceptable (at today's comfort levels) 9-abreast option in their A300/A330/A340 cross-section. It just doesn't fit. Unless you consider a sidewall curving into your head to be comfortable.

And judging from the overlay above, that doesn't look very comfortable. You'd have to scrunch over pretty far to fit in that seat in an Airbus configuration, don't you think?

The 787 is 15 inches (38 cm) wider inside at the head and shoulders level of the seated passenger - where it matters most.

Let's talk about it a bit more, because Airbus often says there isn't much difference between the 787 and their product. They say the difference in the fuselages amounts to only a 4.5 inch (11 cm) advantage for the Dreamliner at the widest place.

Well, the only problem is that once again Airbus is talking about exterior dimensions. And because we have differently-shaped fuselages, the widest places on the airplanes - measured from inside the passenger cabin - are not necessarily in the same spot.

The Airbus airplane has a single, circular fuselage - which means its widest point falls somewhere nearer the floor in the passenger cabin. What that means to you, the passenger, seated at the window, is a steep slope at the head and shoulders - sacrificing your comfort, and airlines' flexibility.

With the 787's larger double bubble, you get a straighter sidewall and less of a slope.

But wait. There's more. Even though the A350 will not have a new fuselage, Airbus has announced it will have a "new wider cabin." They claim to have redesigned the frame structure and liner, and reshaped the bins, to provide - according to Airbus - about three more inches.

Well, you can see above that even allowing for Airbus' claim, they still don't have the ability to provide comparable comfort levels at 9-abreast. It would still fall short by about 12 inches (30 cm) - measured at the passenger's head and shoulder level.

So, from the point of view of that unfortunate window seat passenger, 9-abreast is still not a viable configuration on the A350.

This brings me back to the 8 vs. 8 or 9 vs. 9 comparison question.

Clearly, if you're comparing these airplanes on per-seat efficiency measures, such as fuel consumption-per-seat, or cost-per-seat, then I think the appropriate comparison is the 9-abreast 787 vs. the 8-abreast A350.

Otherwise, if you ever happen to be a passenger seated by the window in any 9-abreast A350, I'd suggest you "mind your head."