Pretty sure windows are required so that passengers can see outside in case of an emergency.

Fair point - I was on a plane and on landing saw the wing flap act in an unusual way (didn't fully open compared to other flap and seemed like it was limited/stuck on one edge and one end raised more than the other and down end shaking and wasn't what I'd seen on that type of boing before). I pointed this out to the staff, who thanked me. Might of been nothing, and not something you follow up or indeed, how you would follow up. But equally, may of been sign of something amiss.

>However, aviation regulator the European Aviation Safety Agency said [in reference to windowless planes]: "We do not see any specific challenge that could not be overcome to ensure a level of safety equivalent to the one of an aircraft fitted with cabin windows."

https://www.bbc.com/news/business-44383220

Don't they just need windows at emergency exits? Passengers are already supposed to await cabin crew instructions before they evacuate, and passengers probably aren't really that great at evaluating danger aside from the obvious signs like fire or being under water, but the exit door window would also tell you that.

Or more importantly so that the rescue service can see in.

You could have cameras and screens instead of windows. Much, much cheaper in the end.

Windows tend to work slightly better after running into the ground than cameras, electrical systems and screens do.

(A broken window still lets you see outside)

You don't need to have a window on every seat. You could have a few real windows on the side and complement the missing ones by screens.

Doesn't seem like the kind of thing you can rely on in an emergency.

Maybe, though such footage would be useful in a black-box for post-incident/post-flight analysis as a visual comparison to the recorded control/instruments - could only help.