So, when the cabin is sealed, the interior pressure is equal to the atmospheric pressure at sea level. When the plane lands, the exterior pressure is equal to the interior pressure. So why does the plane need to be pressurised for the duration of the trip?
In: Engineering
A lot of people have misunderstood that question. So i’ll leave out the “why humans do bad at low oxygen pressure and why we shouldn’t do that” bit.
The cabin is not sealed – the air is actually being constantly replenished, under pressure. Think of it like a balloon with a pinprick leak. If you blow into it faster than it is leaking out, then the balloon will stay inflated. This is important because as people breathe in the cabin, oxygen would slowly be replaced with carbon dioxide. You could filter this, spacecraft style, but that’s heavy and expensive. Much easier to just replace the air with fresh (compressed) outside air.
Even if that wasn’t an issue, having a perfectly sealed cabin would spell trouble on flights to different cities. They are at different elevations, and this different ambient pressures. A flight from Los Angeles to Denver would leave the airplane pressurized relative to the outside, creating hazards and a very uncomfortable sudden jump when the doors are opened.
For the same reason that a bouncy castle has a blower constantly pushing air in, rather than being inflated once and left alone: its *way* easier to make something that is only mostly airtight, and then little leaks aren’t a problem.
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