Why Do Airplane Windows Have Tiny Holes?

If you have ever sat in the window seat of an airplane, you will know that airplane windows are small and sealed shut; however, there is a tiny, often overlooked detail of all airplane windows that serves an important purpose: a small hole at the bottom. Also known as bleed holes, these aspects of aircraft windows allow us to breathe at the high altitudes of flight by keeping the cabin pressurized. In order to maintain proper air density, aircraft have systems in place to keep pressure levels steady. In the following blog, we will take a closer look at how this is accomplished and the vital role of the tiny hole.

Pressurization in aircraft cabins is what prevents the air that all passengers, pilots, and crew breathe from becoming too thin and depleted of oxygen as the plane climbs in altitude. In fact, the face masks the flight attendants teach passengers to put on at the beginning of a flight are the emergency protocol for if pressurization fails. At any point in the sky above 10,000 feet, human beings cannot breathe safely, hence the announcement the pilot makes when the aircraft is flying at such an altitude. With pressurization in cabins, aircraft may reach cruising altitudes as high as 33,000 feet, keeping oxygen and pressure levels safely higher than the surrounding atmosphere.

Unfortunately, the pressure difference places an enormous strain on the windows, so they are designed with three distinct layers. The innermost pane is the one we can touch from our seat. It is superficial in that it is not involved in the pressurization process, but it merely further protects passengers from the thinner air. Meanwhile, the middle pane of the window is the layer that contains the bleed hole; this hole is used to balance the pressure difference between the inside and outside air. In the gap between the second and third window panes, the pressure becomes equalized. It forces the outer pane to take the strain of the low pressure outside through this process, and also offers another benefit.

The bleed hole works to prevent window fogging by regulating the moisture and temperature between the inside and outside. As such, we are able to see the spectacular views these windows provide during flight without the interference of moisture, condensation, or other obstructions of sight. Luckily, the pressure within an aircraft is carefully regulated, and we can breathe soundly without realizing we are in a thinner atmosphere. At the same time, it is interesting to know about the pressure systems, which explain the mystery of the tiny hole in aircraft windows.

When you are in the market for top quality aircraft windows and other components of any type, turn to Aviation Purchasing Platform for all of your needs. Owned and operated by ASAP Semiconductor, we are a premier distributor of high quality part types from trusted manufacturers around the world. Supplying only from entities on our Approved Vendor List, we proudly boast access to an expansive inventory of over 2 billion new, used, obsolete, and hard-to-find parts. With AS9120B, ISO 9001:2015, and FAA AC 00-56B accreditation in tandem with a strict No China Sourcing pledge, we ensure that all part types we carry are vetted for fit and function before shipping orders to you alongside their applicable manufacturer trace documents. As we are available around the clock, contact us at any time via phone or email to learn more.


March 20, 2023

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