Joel has always wondered why there are tiny holes in airplane windows, but he’s been too embarrassed to ask. In Travel SOS, Leon explains the purpose served by these holes.
I’ve flown on planes for 40 years and I’ve always noticed the tiny holes in their windows and I know they must serve some obvious purpose but I’ve been a bit embarrassed to ask. So, can you tell me what are the holes for?
A. Joel, that tiny hole in your plane window may not seem like much, but it’s a very important safety feature.
It’s called a ‘breather hole’ or a ‘bleed hole’ and you’ll find them on every window on the plane.
This bleed hole is wedged between two panes of acrylic material: the scratch pane, which you can touch, and the outer pane, which protects you from the pressure difference outside.
Basically, the air inside your cabin is pressurised to match the air pressure on the ground. This is so you don’t pass out or suffer from hypoxia caused by lack of oxygen. The air pressure outside your window is dramatically lower than what’s inside and, to fix the imbalance, all that air inside desperately wants to get outside.
This is where the bleed hole does its job. The hole reduces the pressure on the middle pane, allowing the outer pane to experience the force of cabin pressure gradually during flight.
So, if something just happened to smash the outer pane it would blow out, meaning the middle and inner panes would hold and you can keep breathing.
The little hole also wicks away moisture from in between the panes, preventing the windows from fogging up.
Don’t believe me? Well, take it from a guy who makes plane windows.
“The purpose of the small bleed hole in the [middle] pane is to allow pressure to equilibrate between the passenger cabin and the air gap between the panes, so that the cabin pressure during flight is applied to only the outer pane,” Director of Technology at GKN Aerospace Marlowe Moncur told Slate.
So, the next time you stare out your plane window, just know that little hole plays a very big part in the safety of your flight.
If you have any questions about travel, no matter how ‘embarrassing’, send them to [email protected] and we’ll have a go at answering them!