If you have ever been on a plane and sat next to a window, many of us have probably noticed that there is usually a small hole in the bottom corner of the plane window. In fact, this extremely small design plays a very important role, indispensable on every plane.
Why are there small holes in airplane windows?
Many people wonder why there is a tiny hole in the airplane window. (Illustration photo)
Henny Lim, a flight attendant for Cebu Pacific, a Philippine-based airline, said passengers often ask about the "mysterious" holes in airplane windows and whether there is a hidden reason for them.
The punctures, also known as 'bleed holes', are necessary for safety, she said. "The small holes help equalize the pressure difference between the cabin and the outside air," Henny said in a video.
Aircraft windows are made of three layers of glass and acrylic to keep them insulated and secure. The holes create a controlled airflow and reduce the pressure on the window due to air pressure.
Henny also revealed another purpose – to keep the glasses free of moisture. “These holes release moisture and prevent frost or condensation from obstructing your vision,” she said.
It is essential that passengers can see around them in the event of an emergency landing or similar. The holes allow dry air to circulate between the outer, middle and inner layers - keeping the window clear.
Unexpected uses of small holes in airplane windows
The holes create controlled airflow and reduce pressure on the window due to air pressure.
Although it is a very small design, it has an important meaning, both practical and highly technical, required on the plane. Simply put, that hole plays a very important role in regulating the pressure of the entire plane. It helps to equalize the pressure between the cabin and the outside air. Besides, it also has another purpose: releasing moisture and preventing frost or condensation from obstructing your vision.
When an aircraft reaches a certain cruising altitude, there is a significant difference in pressure between the outside air and the air inside the cabin, which is pressurized to simulate the atmosphere at lower altitudes. Meanwhile, most commercial aircraft windows have three layers: an outer, middle, and inner pane, all usually made of acrylic. The outer glass takes all the pressure of pressurizing the cabin. The inner glass is designed to hold cabin pressure in the “extremely rare” event that the outer glass cracks.
The purpose of the vent, located near the bottom of the middle pane, becomes clear. It acts as a relief valve, allowing the air in the passenger cabin to equalize pressure with the air between the outer pane and the middle pane. This tiny hole ensures that the cabin pressure during flight is only exerted on the outer pane, thereby preserving the middle pane in an emergency.
If cabin pressure blows out the outer pane, which is rare, the inner pane is strong enough to hold the pressure, giving the pilots time to descend and depressurize the cabin. According to the Boeing 737 maintenance manual, the center frame is designed to maintain 1.5 times normal operating pressure at 70 degrees Fahrenheit (21 degrees Celsius).
These little holes also have a secondary, but much more straightforward, purpose: to help passengers get better views (and photos) of the sky outside the plane. They also help prevent condensation or fog from forming between the panes, which can obstruct the view for passengers who have paid extra for a window seat.
In other words, it is best for passengers to not touch the hole in the window or cover it so that it can do its job effectively. Every design on an aircraft, no matter what type of aircraft, has been carefully studied, calculated and designed to ensure safety and the best possible flying conditions.
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