The small hole you see in airplane windows is called a "bleed hole" or "breather hole." It is intentionally designed as part of the aircraft's window structure and serves an important purpose.
Airplane windows consist of multiple layers to ensure strength, insulation, and cabin pressurization. The outermost layer, typically made of sturdy acrylic material, protects the inner layers from external factors like wind, temperature, and pressure. The bleed hole is usually located in the middle or innermost pane of the window.
The primary function of the bleed hole is to regulate the pressure between the inner and outer window panes. During flight, there is a significant difference in air pressure between the aircraft cabin and the external atmosphere. The cabin is pressurized to provide a comfortable environment for passengers, while the external atmosphere at cruising altitudes is at a much lower pressure.
The bleed hole allows a controlled flow of air to pass between the cabin and the area between the window panes. This equalizes the pressure, preventing excessive stress on the window structure. It helps distribute the pressure load evenly across the window and reduces the risk of the window cracking or shattering due to the pressure differential.
Additionally, the bleed hole also helps prevent the formation of condensation or fogging between the window panes. Moisture or humidity can sometimes get trapped between the layers, and the bleed hole allows any moisture to escape, keeping the windows clear and maintaining visibility.
In summary, the small hole in airplane windows, known as a bleed hole, plays a crucial role in regulating pressure and preventing fogging or condensation between the window panes, ensuring the structural integrity and visibility of the windows during flight.