If you have ever sat in a seat next to the window aboard an airplane with its shade raised, you might have noticed a small hole in the bottom of the window in addition to the breathtaking scenery of the sky, the clouds, and the landscape below — and you probably wondered why that small hole is there.
Why Is a Tiny Hole in the Airplane Window?
That little hole in the window pane is known as a bleed hole — and it helps to regulate air pressure changes in order to keep passengers safe and comfortable as airplanes climb to cruising altitudes of up to 36,000 feet.
Air pressure and oxygen levels are significantly reduced at higher levels in the atmosphere; so cabin pressure and oxygen levels are maintained at levels which are higher than the surrounding atmosphere — but the difference in pressure results in the windows potentially undergoing enormous physical stress and strain; so windows aboard airplanes are designed and engineered with three distinct layers which are comprised of acrylic and not glass:
The inside pane which we can touch while seated inside the aircraft is basically superficial — but it does serve the purpose of helping to protect the middle pane and outer pane of the window from any possible damage which could be potentially caused by passengers
The middle pane and outer pane are the layers of the window which regulate the differences in air pressure
The bleed hole is located at the bottom of the middle pane and causes the outer pane to endure the physical stress and strain of the low air pressure outside by allowing the air pressure to equalize between the passenger cabin and the gap of air which is between the panes
Bleed holes also prevent the window from fogging up or frosting over by regulating the temperature of the air between the inside and outside, which allows passengers to enjoy amazing views during flights.
If you have ever seen a bleed hole and were concerned about it, do not be concerned — even if you start to see a little frost form around it. That little hole is purposely designed to be there so that you may enjoy your flight a hole lot more safely.