Tuesday 24 April 2018

Why do airplane windows have those tiny holes in them?

Travel Truths

Airplane window. Photo: Getty
Airplane window. Photo: Getty

Gavin Haines

It's a question many frequent fliers will have pondered: why exactly are there tiny holes in plane windows?

Surely we shouldn’t have holes in the windows of planes?

On the contrary. Those holes, which are only present in the middle pane of our triple-glazed planes, are actually there to keep us safe.

Without them, passengers could be in trouble.

But before we explain how these “bleed holes” help keep us alive, it’s important to understand how air pressure changes when you’re climbing to 33,000 feet.

As anyone who has scaled a mountain will know, at high altitude the air is less pressurised and contains less oxygen; hence why climbers suffer from altitude sickness. And that’s just a mountain; at cruising altitude the pressure outside is even lower.

Inside the plane it’s a different story: to make sure those onboard don’t pass out, the cabin air is pressurised, which places an enormous strain on the windows.

The inside pane – the one you may have woken up against from time to time – is largely superficial, meaning the middle pane and outer pane are taking the brunt of the pressure.

Cue the bleed hole, which relieves some of that pressure, allowing the outer pane to gradually take the strain.

“The middle pane is the one with the small hole in it,” says Justin Dubon of Airbus. “The purpose of that hole is to allow pressure to equalise between the passenger cabin and the air gap between the panes.”

That little hole also stops the windows from fogging up, meaning you can watch the scenery below unfold as you travel to your destination.

So now you know. Go forth, and impress fellow passengers with your trivia.


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