What controls the air for cabin pressurization on an aircraft?

• A. Outflow Valves
• B. Inflow Valves
• C. Cabin Pressure Regulator
• D. Air Conditioning Pack

Answer: (A)

The key idea is that cabin pressure is controlled by venting, not by the supply of air. Air for the cabin comes from the air conditioning packs using bleed air, but the actual regulation of cabin pressure is done by the outflow valve. The cabin pressure regulator monitors the cabin altitude and differential pressure and moves the outflow valve to open or close, setting how much air escapes to the outside. By adjusting the venting rate, it maintains the commanded pressure inside the cabin. Inflow valves don’t regulate the pressure; they don’t control how much air leaves the cabin. The packs provide conditioned air, but the valve that determines the cabin pressure by balancing inflow and outflow is the outflow valve.