What is the hole in the window on a A320 for?

Question

I went to Greece last month and noticed that in all the windows, they all have a tiny circular hole in the middle at the bottom, and was wondering what it is for.

I've been on other planes too, and think they have them, but i'm not 100% sure.

:3

Answer 1

Good answer David, but not completely correct.

The outer pane carries pressure, and the little hole lets cabin pressure into the cavity, but it is not there for insulation.  It is a fail-safe pane- if the outer pane fails, the inner one can indeed carry cabin pressure (the loss through the little hole is insignificant so the airplane will stay pressurized).  It can't carry it for thousands of flights, like the outer pane, but will get the airplane to the ground safely without a depressurization event.

The frost is condensation from the moister cabin air contacting the cold outer pane.

Answer 2

all other planes all have those, well, commercial ones anyway.

the windows are double paned to insulate the cabin. What you undoubtedly know is that the cabin is pressurized. Notice the inside pane is of plastic and the outside one is made of considerably stronger glass or Plexiglas. To save weight, they made the inside pane of plastic. However, the plastic cannot stand the pressure differences, so they holed the inner pane so that instead of it taking the strain, it's the outer, stronger and heavier glass that's doing the job.

edit: the outer glass is very cold. Which makes the air in between the two panes cold. The air in the cabin is much warmer, so the temp difference makes frost appear. (in conjunction with the moisture that is present) By the way,  the inner pane isn't necessarily plastic. Just a lighter material, acrylic for example.

edit2: of course, in an emergency, the inner pane becomes the pressure bearing pane but when the outer pane doesn't fail, that's what the hole is for. failure of the outer pane isn't that common anymore.

Answer 3

thats where you point your gun out of