If you have ever traveled in an airplane, you may or may not have noticed a hole at the bottom of each window. This is one feature that is common across all passenger planes. You might be wondering why anybody would bother leaving a hole at the bottom of an airplane window but it actually plays a role in the safety of the airplane itself. Malowe Moncur, director of Technology at GKN Aerospace explained how it is important for regulation of the pressure in an airplane’s cabin.
These holes keep the external atmospheric pressure constant within the panes. The pressure created by the engines of the airplane compresses it to create the thrust. This air is maintained within the cabin with the outflow valve. Thus, this breather hole in the airplane functions as a bleed valve. The sensors determine the amount of pressure present in the cabin upon which the valve releases the air at a constant rate in order to maintain a certain level of air pressure.
The valve opens up once the airplane is stationary and starts to close once it takes off. The air at sea level is recorded at 14.7 PSI while a airplane travels at a height ranging from 9,150 to 12,200 meters. Head of Advanced Structural Testing Centre at the University of Sheffied Advanced Manufacturing Research Centre, Philip Spiers mentioned, “at high altitudes there are not enough oxygen molecules to sustain life. Low pressure lowers the boiling points inside the body and at the edge of space, this can cause blood and tears to boil.”
He went on to state, “Planes have a higher pressure inside than outside. It’s like a bottle of Coca-Cola – shaking a bottle makes it go stiff and hard but when you undo it, it becomes floppy again. This stretches the skin around the plane.” The pressure inside the cabin is maintained at 11 PSI – same level of pressure experienced at around 2,130 meters. If the pane was sealed [and didn’t have a hole in it], all the pressure in the cabin would act on the inside pane of glass.”