The device responsible for automatic cabin pressurization regulation is the

• A. Outflow valves
• B. Main exciter
• C. Expansion turbine
• D. Pitot tube

Answer: (A)

Automatic cabin pressurization regulation is achieved by controlling how much air leaves the cabin. The outflow valve is opened or closed by the cabin pressure controller based on the sensed differential pressure between the cabin and the outside. As the aircraft climbs or descends, the controller adjusts the valve to maintain the preset cabin pressure, venting excess air to the atmosphere as needed. The other devices do not regulate cabin pressure in this way: the main exciter is part of the electrical power system, the expansion turbine is part of the air conditioning cycle but does not directly regulate cabin pressure, and the Pitot tube measures airspeed, not cabin pressure.