This doesn't refer to the double-paned outer window, the pressure window. It refers to the innermost protective pane, the "scratch pane" that keeps greasy fingers and portruding camera lenses from reaching the two "real" windows. It's the hole in the scratch pane people are asking about
> doesnt mean the inside one isnt there to protect the outside one.
The inner pane is typically half the thickness of the outer pane.
So whilst you could argue it cold be seen as a failsafe, I would say its primary purpose remains "double glazing" insulation.
The OAT at 30–40,000ft is very low and there is a lot of combined window area. So the importance of insulation is not to be underestimated. In particular on newer aircraft where efficiency is the name of the game in their design.
Also if it wasn't insulated, the windows might also steam up? Or does the air conditioning make it dry enough that this wouldn't happen. Foggy windows could also affect the pilot's ability to see, I suppose the flight deck windows must also be insulated.
> Or does the air conditioning make it dry enough that this wouldn't happen. Foggy windows could also affect the pilot's ability to see, I suppose the flight deck windows must also be insulated.
Depends on the aircraft but a typical design would connect the space between the panels to an air supply or otherwise a self-contained desiccator system.
Flight deck windows are completely different, typically three layers, two full thickness and one half thickness. All fully heat/chemical strengthened with additional anti-fog, anti-ice and moisture absorption systems built-in. The fact that some of them are sliding (i.e. openable) adds to the design complexity.
that's not what's being discussed. airplanes have a hull window and a passenger cabin window that are universally refered to as a single "double" window- at least amongst the general public.
The inner cabin window is absolutely there to protect the hull window.
