Drilled holes in the lower part of aircraft windows

[tb10er]

Something I've always wondered and never yet worked out.

Normally I sit on an aisle seat so tend to forget about it but today I managed a window seat so, be an nosey thing that I am, decided to watch the world pass by. I then noticed the small "holes" (ok, they are only shallow) drilled into the bottom of each window. I remembered that this is the best place for answers to state what their purpose is.

Many thanks

[mitzy69]

the little hole is only in the inner of the two plastic window pressure panes at passenger positions.
the outter pane does not have a hole and takes the pressure difference of inside to outside pressure of 8 psi.
if this pane fails or blows out then the inner pane takes the pressure plus a small leak of cabin air out of the little hole.
between these plastic panes and passengers is a third pane of plastic which is there to stop the pressure panes being scratched and damaged by acid sweat and ball point pens.

[Tinstaafl]

I thought the small hole was to allow pressure equalisation between the cabin and the space between the passenger-facing window and the exterior-facing pressure window. I imagine it would help reduce condensation too.