Why do airplane windows always have a small hole?

Airplane windows are not just panes of glass. They consist of three separate layers:

The outer window: It supports all the pressure generated by the difference between the inside of the cabin and the outside.
The central window: A safety layer, designed to intervene if the outer window ever gives way.
The inner window: Located near the passengers, it is not subject to any pressure and mainly serves as protection against accidental scratches or knocks.
The crucial role of the "bleed hole"

Airplane window breather hole bleed hole with wing blue sky

The famous little hole, located on the central window, is called a "bleed hole". It fulfills two essential functions:

Balance air pressure: This hole allows limited airflow between the cabin and the space between the central and outer windows. This ensures that only the outer window bears the pressure.
Prevent condensation: By evacuating moisture, it prevents the formation of fog that could obstruct the passengers' view.
A discreet but essential detail

This little hole, although tiny, is a perfect example of the precision of aeronautical design. It ensures both your safety and comfort, maintaining a clear view during flight.

Next time you're sitting by the window, take a moment to look at that little hole and think about its crucial role. Even the smallest things can be very important. Have a great flight!