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
>So, when the cabin is sealed, the interior pressure is equal to the atmospheric pressure at sea level.
That is a pressurized cabin. The alternative is on where air can flow freely in and out so it is not sealed.
If you had a perfect sealed cabin and just closed the door at takeoff and nothing leaked out during the flight you have describes a pressurized cabin with no air replacement. The pressure at altitude is lower then att takeoff so if the pressure is higher inside if is is sealed ie a pressure cabin.
You also need to refresh the air because the oxygen level would drop and carbon dioxide levels would increase. So you compress air from the outside and let it in it in the front and let air leak out in a controlled way.
In practice, you do not use sea level pressure but the pressure that is at 8,000 ft (2,400 m) or below. The airplane expands slightly when the pressure inside them is higher than the outside and is stresses the airframe. So you need thicker material, more maintenance and perhaps a shorter life for the aircraft it the pressure inside was higher.
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