# What would prevent the installation of windows on the roof of an airliner?

What prevents airline manufacturers from putting a strip of glass along the roof of the aircraft? It would be a good addition in terms of cabin view, light inside the cabin, etc.

Would it compromise the structural integrity too much?

Edit: The image is for representational purposes only. My question does not pertain to a installation similar to this image

• Ironically, the picture you posted is for a windowless aircraft concept, where screens replace windows completely. That seems like a much easier way to give passengers an all-around view than dealing with the structural issues of huge gaps in the fuselage. – Pondlife Jul 22 '15 at 12:52
• That's all good and neat and all, but oh my god, I would wager way more people would experience vertiginous gastronomical expulsions than desired. – CGCampbell Jul 22 '15 at 13:07
• Even with highly reflective glass, it would get uncomfortably hot in the cabin. The idea is to get sunburn on the beach after you arrive, not in a plane on the way there. No flying greenhouses for me. – Martin James Jul 22 '15 at 13:26
• I know that aquariums hold back massive amounts of water pressure with glass, but that glass is massively thick. How in the world would you pressurize an all-glass hull like that with glass thin enough to get it off the ground, and how would it take all the stresses of take-off and landing? – FreeMan Jul 22 '15 at 13:28
• vertiginous gastronomical expulsions - @CGCampbell, that is quality word smithing right there! – FreeMan Jul 22 '15 at 14:45

There are a few factors involved in this and you should check out this answer that touches on window size (same issue really). For what its worth the ceiling is prime real estate on an aircraft. Modern airliners have the over head baggage compartments there (which provide a remarkable amount of space)

The area is also used to run cabling (electronics mostly these days) fore and aft as well as power to the reading lights etc. However it should be noted that these things could most likely be routed along the floor just as well.

The real issue comes back to windows being a weak point and glass being heavy. When it comes to planes you want them to be as light as can be so excess windows will only reduce useful load and increase potential failure points. On top of all that you will have more ambient light in the plane which may bother those trying to sleep on late night flights.

If you want a better view fly an unpressurized plane!

While on the topic of small bubble canopy planes, anyone that flies GA planes (especially like the ones shown above) with out air conditioning will tell you how hot it gets on the ground (and even at lower altitudes flying) in the summer. The canopies make the inside of plane behave like a green house and really heat up. This would make the inside of a jumbo jet really bake in the summer while taxiing (which can be a long process at big airports).

• For a second (while still reading the text above) I though the yellow plane was a model that was somehow balanced on the windshield of the white plane... – Michael Jul 22 '15 at 19:17
• I don't know about GA, but a C-130 gets ridiculously hot on the ramp, despite having basically no windows in the cargo compartment. Running the A/C helps a bit, but there's only so much it can do. – Geobits Jul 23 '15 at 4:35
• If glass is heavy, i am sure other composites could be used... If the windshield glass in front of the pilots can take the pressure, i am sure glass on the roof can handle it too.. Also, it need not be a huge area of glass, a thin strip would also do... – Firee Jul 24 '15 at 6:33

The same thing that prevents them from just having glass down the entire length of the fuselage, rather than discrete windows: the ribs of the frame.

This picture from cpast's answer on UX.SE shows how the windows are placed relative to the frame:

On smaller aircraft, they probably could install small windows like the ones beside the passengers in the roof of the aisle, but it would add design complexity and also heat up the cabin (especially when sitting around on the ramp.) I'm assuming the cost/benefit ratio there was just deemed not worthwhile. Having them directly above the passengers wouldn't work because that's where the overhead storage bins are.

In the case of wide-body aircraft (like the one picture above,) note that the actual top of the fuselage is quite high. In addition to the overhead storage bins above the passengers, there is often other stuff between the ceiling of the passenger cabin and the actual top of the fuselage, such as crew rest quarters, pipes, cables, or, in the cases of the 747 and the A380, another entire passenger cabin.

An additional problem with this is that it would make it harder to control cabin lighting, unless the windows were electrically dimmable, like the new ones on the 787. Longer flights will usually want the passenger cabin to be dark-ish in order to accommodate the passengers who want to sleep. With the windows beside them, passengers can open or close their window depending on how much light they want. That wouldn't work for windows in the ceiling (since they would affect multiple rows of passengers.)

Window size limitations are also discussed in Why aren't airliner windows aligned with their seats? and the previously-linked question on UX.SE.

One other consideration is that the crown of the fuselage is under significant tension*, and glass does not have appreciable tensile strength.

*Think of the fuselage as a tube being held up midway along its length (i.e., by the wing). The weight of the fuselage and its contents will cause bending about the center wing box, putting the crown in tension, the keel in compression, and the sides under shear. The shear can be channeled around the window frames but normal loads would require far more structure for the same.

The structural arguments have already been discussed, but a further thing to consider is that there really is no point.

For the small windows on airliners (necessarily small for the structural reasons outlined) the only person who gets a decent view is the person in the window seat, who has a wide angle view by virtue of being right next to the window.

The person in the aisle seat (or the centre block of a widebody) is lucky if they catch a glimpse of land out of the window.

A window on the ceiling of an airliner, besides being to far from anyone to give anyone a decent view, would be be pointing straight up at the sky. All you would see would be blue sky, cloud (under certain weather conditions while below cruise height) and blazing hot sun.

I recently flew from London to Guanzhou, China, on a 787, on which the designers made the appalling high-tech decision of using dimming windows instead of traditional shutters. The windows don't dim all the way to black, and the sun shining through the window is a real distraction when you're trying to sleep. Who would control the shutters on roof windows in an airliner?