An expert has explained why there are tiny holes in plane windows.
If you've ever stared out the window as your plane takes off, you will have seen a tiny hole in your window.
At first, it may seem like a weird addition, especially in something that's carrying a lot of people at a great height where the outside is unforgiving and cold.
It can come across a little at odds with the super-high tech nature of modern aircraft.
Happily they are not there by mistake, but for a very important reason: to stop the cabin from de-pressuring.
An expert from the Federal Aviation Administration told Tech Insider that the hole is used to regulate air pressure.
As the plane gets higher up, the air pressure outside drops compared to the regulated air pressure inside the cabin.
As the difference between the two increases, so does the physical stress being pressed onto the windows, which are made up of three panes of glass.
There's a small air gap in between the middle and outer panes, and the hole is actually in the middle pane.
If you ever wondered what it's called - it's a "breather" or "bleed hole - and it balances the pressure between the cabin and the air gap.
The outer pane takes the pressure, whereas the middle pane acts as a fail-safe just in case that trusty outer pane fails.
The hole has another role though - releasing moisture from the gap preventing the little windows from fogging or frosting over.
So next time you see the tiny fracture like lines rather than a not so lovely cloudy window, you know why.
The presence of the holes, and their function, has sparked quite a reaction on Twitter.
One person fretted: “Everything about a plane is scary.
"Especially the bleed holes if you don't understand why you have a hole in your window and don't realise it until you're 30,000 feet in the air.”
Another user added: “Quite shocking how important window design is for a plane.”
A third person questioned: “What if some kid puts their finger over it.”
Someone else confessed: “All the times I've travelled via airplane (international and local) I've always sat beside the window.
"The day I eventually discovered the bleed-hole I thought it was a defect.”
