What does the pressurization system do and how is cabin pressure controlled?

• A. Maintains cabin pressurization by regulating outflow valves and differential pressure; maintains target cabin altitude.
• B. Controls cabin temperature.
• C. Provides oxygen supply to crew.
• D. Maintains cabin humidity.

Answer: (A)

The main idea is that cabin pressure is kept by balancing the air the system supplies with the air it vents overboard, so the cabin stays at a safe, comfortable altitude. Air from the environmental control system fills the cabin, while an outflow valve vents air to the outside. A pressurization controller monitors cabin pressure and the outside ambient and automatically moves the outflow valve to hold a target cabin altitude and a safe differential pressure between inside and outside. If the valve vents too little, cabin pressure rises; if it vents too much, it falls. A relief or safety valve protects against overpressure. This is why the system’s job is described as maintaining pressurization by regulating the outflow valve and differential pressure to keep the cabin at the commanded altitude. Temperature, oxygen, and humidity are handled by other systems, not the pressurization controller itself.