There’s a hole in my window!

Certain things defy logic – like the tiny hole on airplane windows.

Don’t they disrupt the pressure in the cabin…affect the oxygen level maintained within?

Airplanes are complex structures of engineering excellence. They have so many head-scratching elements around them that a lay person is wont to dismiss most with a ‘they know best’ refrain.

But not that hole in the window, the one that has befuddled many a passenger. While majority prefer to hold back their queries, for fear of demonstrating ignorance with the whys and how’s, there are some Oman Air flyers who have inquisitive minds and have wondered aloud, on many an occasion, the exact role of that tiny hole.

For them, and for the large ilk of flyers from different walks of life, here is a quick look at that tiny hole:

No, it isn’t put there to spook flyers, to enhance the aesthetics of the windows or to ensure good luck. It has a very specific role, one that it silently enacts every time the plane is high above the skies.

That hole on the window is there to ensure your safety. You read that right: your safety! While it is common knowledge that the pressure within the aircraft is maintained at a certain level so that passengers are able to breathe without difficulty, even at altitudes of 35,000 feet above sea level, what is, perhaps, not so obvious is that the aircraft, as a structure, also experiences similar pressure when it rises high in the air – the pressure outside the plane is much lower than the inside. It is this difference in pressure that puts a stress on the window. It needs a release of some kind to ensure it does not burst at the seams, so to say. That little hole provides a breather for the plane; an option to exhale when it is choking with pressure inside.

Called ‘bleed holes’, they are inserted in the centre pane that is sandwiched between two other panes – the ‘scratch pane’ is the one that passengers can touch and feel, in the middle is the pane with the tiny hole and the outer pane is the one that seals and protects all the panes.

Although sandwiched, it is the middle pane with the hole that protects the other two panes. It ensures that the difference in pressures – within the aircraft and outside it – is balanced between the panes. The tiny hole is also responsible for releasing moisture and minimizing the frost/condensation that could otherwise clog the window.

With aircraft pressure well calibrated and maintained, passengers rarely, if ever, notice the ebbs and flows of pressure outside. The air within is conditioned to perfection to ensure that the change in the altitude doesn’t create any loss of oxygen and cause faintness of breathe or hypoxia. The situation is akin to what mountain climbers would experience if they weren’t geared up for the adventure. To explain it on a more technical platform, the American Vacuum Society has tabulated the pressure at sea level as 1.0 kilogram per square centimeter, which is the ideal breathing pressure. As the aircraft reaches a height of 35,000 feet above, the pressure could drop to 0.2 kilogram per square centimeter, creating a huge difference in pressures at ground and on air.

Thanks to the tiny hole in the window, the increase in the cabin pressure is applied only to the outer pane. In the eventuality of the outer pane getting broken by debris, the middle pane will act as a shield against the dip in the outside pressure, ensuring that the passengers are safe and breathing right.