Aircraft Pressurization: The Basic Idea
Pressurization puts air into the cabin and controls how much can leave. Think of the cabin as a bubble that keeps the air inside at a more comfortable pressure while the airplane climbs.
Where does the air come from?
In the pressurized Cessna P210 example, the turbocharger’s compressor supplies the air. The air is cooled and routed into the cabin. Many jets use compressed air taken from their engines. Turbocharging by itself does not mean an airplane has a pressurized cabin.
What controls the pressure?
- Cabin-pressure controller: lets the pilot select the cabin setting and control how quickly it changes.
- Outflow valve: regulates pressure by controlling how much air leaves the cabin.
- Safety valves: protect the cabin from excessive pressure differences.
- Dump valve: provides a way to release cabin pressure.
Two terms to remember
Cabin altitude tells you what altitude the air inside the cabin feels like. Pressure differential is the difference between the air pressure inside and outside the cabin.
What matters to you as the pilot?
Watch the cabin indications and know the airplane’s limitations. If pressurization is lost, follow the checklist, use oxygen as required and make an appropriate descent. A legal oxygen minimum is not a guarantee that everyone will feel well at that altitude.
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