Airplane Cabin Pressure

Q: How is a cabin pressurized? Why is it pressurized? Does this have anything to do with the size and shape of the windows?

Without pressurization, there would not be enough oxygen for passengers to breathe. As you go higher, the amount of oxygen decreases. Pressurizing the cabin re-creates the conditions on the ground (or close to it, as normal cabin pressure aboard a plane is actually a little higher than sea level). Otherwise, imagine having to sit there with one of those plastic masks strapped to your head. Also, a pressurized cabin allows for a gradual equalization as you climb and descend, making it more gentle on the ears. Pressurization is maintained via air from compressors in the engines. It is regulated through various valves in the fuselage.

The small size of the cabin windows is due to the necessity to withstand the forces of a pressurized cabin. This is why, for example, the windows of Concorde, which operates at a very high cabin pressure, are so tiny. The roundness allows for an even dispersal of the energy.

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This Q&A is part of a collection that originally appeared on Salon.com. Patrick Smith, 38, is an erstwhile airline pilot, retired punk rocker and air travel columnist. His book, Ask the Pilot (Riverhead) was voted “Best Travel Book of 2004” by Amazon.com. Patrick has traveled to more than 55 countries and always asks for a window seat. He lives near Boston.