155) “Some people claim to have seen the curvature of the Earth out their airplane windows. The glass used in all commercial airplanes, however, is curved to remain flush with the fuselage. This creates a slight effect mixed with confirmation bias people mistake for being the alleged curvature of the Earth. In actuality, the fact that you can see the horizon at eye-level at 35,000 feet out both port/starboard windows proves the Earth is flat. If the Earth were a ball, no matter how big, the horizon would stay exactly where it was and you would have to look DOWN further and further to see the horizon at all. Looking straight out the window at 35,000 feet you should see nothing but "outer-space" from the port and starboard windows, as the Earth/horizon are supposed to be BELOW you. If they are visible at eye level outside both side windows, it’s because the Earth is flat!”
The curve of an airliner hull is mostly cylindrical, not spherical, so any distortion would be to vertical lines, not horizons. In any case, you could see such distortion clearly when looking at airport buildings, runway edges etc before take-off. And you don’t. I checked this on my last flight a few weeks ago.
I also noticed that the windows are set a little below the typical eyeline of most people. Why? presumably because designers realise that passengers will want to be able to look down at the ground during their flight – after all, that’s where most of the scenery is. So that’s why you can see out of both side; by design!
In order to start to see a “ball”, you would have to be much higher than the operational ceiling of any airliner in service today.