What is that small little hole at the bottom of airplane windows?

the failsafe pane vent. the little hole allows cabin air to flow into the space between it and the outer pane.

if the outer window fails, the air between blows out and the inside pane keeps the cabin (relatively) sealed.

yup, a vent.

When you envisioned Fluther, I bet you didn’t expect you’d get answers about these kind of mysteries of life. Right?

What causes the circle of frost? Anyone?

@andrew i’m going out on a limb here, but i’d guess the temperature difference? the tempered air from the cabin, quickly cooling as it meets the cooler outside window temperature; air is constantly blowing in from the cabin. that one’s a guess

@eponymoushipster But why a narrow ring of frost, about 1/2 an inch away from the hole?

@andrew i’m not really sure. this is entirely a guess here, but perhaps the air temp is just right there that the water condenses and then freezes at about 1/2 in from the little pressue hole.

So if someone put a tiny piece of chewing gum in that hole, it would be a really bad idea?

Great question, @andrew! I’ve always wondered this.