There is a hole in the window!

Today’s blog is about the small things that play a big part in the world of aviation that go unnoticed by many and are taken for granted by all. No, this is not about thrust or lift or the forces of engineering that keep a Boeing 787-900 weighing a maximum ramp weight of 247 tones (247,208 kg) in the air for a maximum range of between 14 800 km & 15 750 km … No, this is about your window.

A small hole in your window

Have you ever noticed that small hole in the bottom center of your window? This is known as a bleed valve or bleed hole and allows pressure to be balanced between the passenger cabin and the outer fuselage. There are a total of three window panes and the bleed valve is located on the center window pane. This bleed valve is a big part in the health and well-being of all those on board because as the altitude increases, the pressure decreases. So the bleed valve allows for the pressure to be at a safe level for you to breath safely and normally. The bleed valve also releases the moisture from the gap between the inner and outer window panes which allows the window to mostly remain fog free.

Why is an airplane window curved?

There is also a method to the madness of the curved windows. Curved windows allow for the pressure to flow freely around the edges to avoid pressure buildup in the corners of the window. Ice also plays a factor as the expected temperatures at 30,000 ft. are around -56.5°C (-69.7°F) where air pressure is less than a quarter of its value compared to the air pressure at sea level. The average cruising altitude of an aircraft is around 30,000 ft. (10 km) roughly the height of Mt. Everest where the pressure drops to around 3.84 pounds per square inches (PSI). To compare; the standard value of the atmospheric pressure at sea level is around 14.7 pounds per square inch.

So the next time you opt for the window seat on your next flight, take a moment to locate that small hole and remember this blog.

I thank you for the time you have taken to read this blog and I would like to thank Wilbur and Orville Wright (A.K.A The Wright Brothers) for starting us off on this amazing journey in the world of aviation which ultimately getting us to where we are today.


Posted by:   Jean-Pierre Muller  | 
Join the conversation Show comments

rorisang pilane

brilliant article ,very interesting .

Carol-Anne Wait

Well done JP.

Julie Perumal

Congratulations on your first blog JP. Excellent, clear and relevant content. Bring it home “small things that play a big part”, so many things that go unnoticed. Excited to see whats next.

Sabine Owen

Well done JP. Very informative. Sabine 👍

Natalia Feimann

Thanks for this interesting content. However the Wright Brothers did not invent the airplane😒

Jean-Pierre Muller

Thank you Natalia, that is a good addition. Is believed that the airplane was invented by the Brazilian pioneer Alberto Santos-Dumont as his invention had wheels, whereas The Wright brothers were set on rails. The Wright Brothers were documented for the first controlled “flight” with control and sustaining heavier than air human flight. Happy 2019 and have a great day!


well done JP.


This is my first time i visit here and I found so many interesting stuff in your blog especially it’s discussion, thank you.

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