Also referred to as a “bleed” or “breather hole”, those tiny holes at the bottom of the
airplane windows parts actually have a purpose. Airplane windows are thicker and stronger than they may appear, and for a good reason.
In order to keep
airplane cabins windows relatively comfortable, a pressurized atmosphere allows for proper breathing and comfortable temperature. What makes this possible while still being able to watch the skies around you is a three-layered window, made to equalize the low pressure outside and the high pressure inside.
Each layer of the window has a specific function to make the system work. The outside window, on the exterior of the plane, is 12mm thick. It serves as a protective layer to keep the outside air out, being the most structurally sound layer. The middle layer is 6mm thick and contains the bleed hole. This hole ensures balance between the high-pressure cabin and low-pressure atmosphere outside. The innermost layer, on the interior of the plane, is 4mm thick, and acts as the insulated barrier. Also known as the scratch pane, is a protective layer to prevent the passengers from feeling the cold temperature outside while the plane is at cruising altitudes.
Now the little bleed hole that some people may never notice has an important function. As we already mentioned, it helps neutralize the pressure inside the cabin to make it comfortable for customers, but it also helps release moisture. This helps prevent fog and frost from building up on the inside of the window. If you have ever noticed that frost may build up slightly in a round pattern, it is the combination of window surface temperature, cabin humidity, and rate of air flowing through the hole.
If there was no bleed hole, there would be unequal pressure in the cabin and outside the aircraft. This can lead to the windowpanes breaking. With the ever-growing technology, airplane windows may not need this bleed hole. The newest plane that does not have this tiny hole is the
Boeing Aircraft 787.