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On a recent airline flight, I noticed that the spacing of the plane's windows was different from that of the passenger seats: some of the rows had a window directly in line with them but for others, the windows were partially obscured by the seatbacks in front or behind.

Is there a reason that the windows aren't manufactured with a regular spacing to align with the seat rows? Does it have to do with the fact that different airlines may be using different seating configurations for the same model of aircraft?

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    $\begingroup$ Your last sentence is the answer to the question: it's the seats that don't line up with the windows, not the other way around. $\endgroup$ – David Richerby Jul 13 '15 at 23:44
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    $\begingroup$ Duplicatish: ux.stackexchange.com/q/73273 $\endgroup$ – inquisitive Jul 14 '15 at 8:22
  • $\begingroup$ If windows were spaced the same as seats, then getting them to line up perfectly may end up costing the airline a row of seats. Not every aircraft is outfitted the same way, and an efficient layout might place windows such that nobody has a window directly adjacent to their seat - fixing this might require sacrificing the efficiency of the interior layout. However, if the spacing of windows does not match the spacing of seats (windows and rows are not sync'd), then you can maximize the number of seats which have an acceptable proximity to a window without sacrificing layout efficiency. $\endgroup$ – Dr. Funk May 2 '17 at 16:33
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  1. Because the pitch of the frames is not related to the pitch of the seats. The windows placement have to cut through as few frames as possible.

You can see it in the following picture, noting that frames are "highlighted" by the vertical riveting

Riveting around an aircraft window

Image source

It is even more evident in the picture contained in this answer on UX.SE:

Windows vs Fuselage frames

  1. Because the aircraft is designed once, but "decorated" by several airlines in several different manners. For example, an A320 or a B757 will have the windows always in the same locations, but depending on the airline that is using it, it will most probably have the seats in slightly different locations.
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Because airliners skimp on spacing and steal your leg room to squeeze in another row of seats.

So why not design the plane with the eventual seat spacing in mind? Airliners can decide their own spacing so there would always be planes where they won't match up.

Also there has to be a certain amount of hull to keep the strength needed for the fuselage to work as it needs to.

So the designers need to make a compromise on number of seats and strength of the hull.

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    $\begingroup$ I'd add that airlines may move seats as they reconfigure the aircraft. This might happen when changing the configuration of seats in the cabin, e.g. adding or removing business class seats or converting economy seats to premium economy. Or installing new lie-flat business seats. Or squeezing the rows closer together and adding more seats. Or setting up a new layout when the aircraft is sold or leased to a new operator. Even if the rows mainly lined up with the windows when the aircraft was new, there will be some drift as an aircraft goes through many configuration changes in its lifetime. $\endgroup$ – Zach Lipton Jul 14 '15 at 0:32
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    $\begingroup$ So the designers need to make a compromise on number of seats and strength of the hull. note that those are often two distinct and separate sets of designers. $\endgroup$ – Federico Jul 14 '15 at 9:03
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    $\begingroup$ Last time I flew (on Easyjet) I noticed that there are about 3 windows for every 2 rows of seats. While I don't disagree with your first statement, the only options open to easyjet would be to reduce the spacing another 33% so that everyone has 1 window, or increase it so that everyone has two (and the latter kind of misses the point.) It would seem that for structural reasons the window pitch is often less than any practical seat arrangement. $\endgroup$ – Level River St Jul 15 '15 at 8:24
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    $\begingroup$ Because airliners skimp on spacing and steal your leg room to squeeze in another row of seats But isn't there some regulation on the minimum gap between seats, especially on safety grounds? $\endgroup$ – Firee Jan 20 '16 at 13:49
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    $\begingroup$ @Firee: no, there isn't (for now, at least). Regulations are phrased in terms of "seconds needed to evacuate the aircraft". $\endgroup$ – Martin Argerami Aug 12 '17 at 11:08
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An aircraft is delivered in a very basic configuration; no seats, and windows running the entire length of the aircraft. The airline is then tasked with choosing and installing their specific makes of not only seats, but also galleys and sometimes lavatories. All of these must fit into that initial basic aircraft, meaning that this layout may not perfectly fit into the "mold" of the original aircraft. This means that there could be some misalignments because the seats could be of different spacing or size than the windows were originally designed for. This system of configuration is better for both the aircraft manufacturer (because it is cheaper to build one basic airframe as opposed to hundreds of slightly tweaked ones) and the airline (because they are able to customize the interior to their liking).

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    $\begingroup$ Aircraft are usually furnished by the manufacturer. But you are right that the airline chooses how it should be done and that each chooses differently. $\endgroup$ – Jan Hudec Jul 14 '15 at 16:29
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When an aircraft is designed, the hull is designed in terms of 'frames' which actually support the main hull of the fuselage. Some air-crafts have provision to include more frames (upto some limit) to increase the length of the plane if later modifications are required. Now, the windows are placed in a regular spacing depending upon the length of each frame on the hull (so basically windows are spaced to remain in between the frames), and this pattern is determined after loads simulation on the aircraft's hull.

Once designed, the insides of the airplane can be modified at will (as this does not determine the 'safety' of the aircraft much), and this is when airliners try to persuade the manufacturer to put seats in a fashion that they can get the desired revenue. This independence in the hull frame spacing and the seat spacing is why the windows are not aligned with the seats.

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The seats are attached to rails underneath the floor which run along the aircraft fuselage. They can be spaced any way the airline prefers, and this position does not have anything common with the window positioning.

You can buy the aircraft seat rails here, and also see how they look like.

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