You do not have to be an aeronautical engineer to understand that an airplane lodge is pressurized to keep us from passing out as we fly through the skies, 11,000 meters (36,000 ft) above sea level. It also stands to reason that, to keep that pressure controlled, the lodge or cabin cannot have any holes in it. So why, you might be questioning, is there a scary looking little hole in all airplane windows? Well, in a word, regardless of what it appears, it is there for your safety. A British Airways pilot, Mark Vanhoenacker, who reports about aviation for Slate, these small window holes are in fact called 'bleed holes', and they are squeezed between two other sheets of acrylic material, which means that when you look through an airplane window, you are in fact looking through three dissimilar sheets of material.
The first of these sheets, the one you can touch and dirty up with your fingers, is known as a scratch sheet. The central sheet is the one with the bleed hole, and the whole arrangement is finished by the outer sheet, the most important one since it protects you from the pressure alteration of the outside. While both the outer and central sheets have the power to repel the pressure from outside the
aeroplane, the effect of the work drops on the outer window because it is the only barrier between you and the clouds.
Before we go into how these windows protect, however, it is more important to know a bit about how air pressure varies when you are soaring. If everything is working well, you should not even notice the pressure reducing outside your window as you sit there enjoying a movie or catching up on your social media routine, if you are lucky enough to have Wi-Fi.
To make you a pleased little traveller, the lodge of a plane makes pressure by thrusting in the conditioned air that mimics the air pressure you are familiar with on the ground. By doing so, you can stay alive throughout the journey without passing out or suffering from hypoxia, a disorder with fatal complications that ascends from a lack of oxygen. But, as you reach higher and higher heights in your happily pressurized lodge, the air outside the plane turn out to be thinner, having less oxygen and pressure.
It is kind of hard to see this change in pressure (unless you are a mountaineer), but using numbers seems to make it a bit cooler. According to the American Vacuum Society, you experience approximately 1.0 kg per square centimeter (14.6 pounds per sq. inch) of pressure at sea level. This is what humans are familiar while feeling and breathing. It is pretty calm.
When you get on a plane and climb all the way up to a traveling altitude of 10,679 meters (35,000 ft), this pressure falls down to an ordinary 0.2 kg per square centimeter (3.4 pounds per square inch).
This means that while you are flying there is a massive different between the pressure inside the
lodge of the airplane and that outside of the plane and all the air inside the plane badly wants to get outside to fix the difference. Thus what does all this have to do with the tiny scary-looking hole in the window? Well, that hole, in fact, decreases the pressure on the middle pane, so merely the outer sheet takes the force of the lodge pressure, and it experiences that pressure more slowly during flight.
Marlowe Moncur, director of technology at GKN Aerospace, a passenger window manufacturing company, described to Slate, "The purpose of the tiny bleed hole in the central sheet is to allow pressure to equilibrate between the passenger lodge and the air break between the sheets, so that the lodge pressure during flight is useful to only the outer sheet."
So that means that if the outer sheet in some way was broken by wreckages, we wouldd still have the middle sheet to protect us from the shortage of air pressure outside. Sure, it would have a small hole in it, but that is nothing the plane's pressurization method could not compensate for. While this small hole plays a vital role in keeping us safe, it also helps keep the window sheets from fogging up, a result of the temperature change between the inside and outside of the lodge or cabin, allowing us to look out into the clouds.
Thank you, tiny window hole. Who knew something so humbly could be so significant?