What is the role of the outflow valve in the pressurization system?

• A. To regulate cabin pressure by venting air from the cabin.
• B. To regulate external air pressure on the wings.
• C. To supply conditioned air to the cabin.
• D. To increase cabin pressure during takeoff.

Answer: (A)

The outflow valve is the vent that regulates cabin pressure by releasing a controlled amount of cabin air to the outside. The pressurization system cleverly balances the air that is being supplied to the cabin with the air being exhausted through this valve. A cabin pressure controller adjusts the valve opening to hold the desired cabin altitude and the correct differential pressure between the cabin and the outside air. If more air is vented, cabin pressure drops; if the valve closes more, cabin pressure rises toward the target. This valve does not supply conditioned air to the cabin, nor does it regulate external wing pressures, and it isn’t used to increase cabin pressure during takeoff—the system increases pressure by supplying air and uses the valve mainly to vent excess air to maintain the set conditions.