Pressurized Cabins

Flying higher is better. The air is less turbulent (most turbulence is caused by the sun’s warming the ground which warms low-level air which creates currents and bumps and queasiness). The view is nicer. And jet engines work more efficiently at higher altitudes. Jetliners were going to fly higher, above 30,000 feet compared to the 10,000 feet that earlier planes could fly.

One problem: much above 10,000 feet, humans start to pass out. Personally, I think 12 hour flights to Sydney in economy seats would be a lot easier if you just passed out 10 minutes after take-off. But the FAA thinks consciousness is safer, and when else is it societally acceptable to gorge yourself on 5 RomComs in a row? Earlier planes that had to fly high used oxygen masks. (Higher is also colder: at around 27,000 feet outside air hits -40 degrees Fahrenheit. This is why Bomber Jackets are leather and wool.) Obviously, paying passengers wouldn’t want to wear masks and insulation.

The answer: Pressurization.The engines’ turbochargers already compress air for the engine, so we divert some of this compressed air inside the plane.  As the plane climbs, the air outside grows thinner, but the air inside the plane stays thick. Well, sort of thick: most planes are pressurized to about 8,000 feet. This is still thinner than we’re used to, so you probably won’t be running any marathons (also, you’d beat the screaming baby for the most-annoying-passenger prize).

This requires a new kind of plane. The skin is now effectively a balloon, holding air inside even as its higher pressure makes it want to escape. A tiny hole anywhere in the skin makes everyone in the plane pass out (surprise!) in the best case. In the worst case, it can be as disastrous as popping a balloon. Engineers deal with this in each plane, adding another complexity that they have to make fully safe while keeping us needy passengers warm, comfortable, and conscious.

[Pedants will point out the B-29 had pressurized cabins. Yes, it did, but the whole plane wasn’t pressurized yadda yadda technicalities.]