What is the purpose of the outflow valve in cabin pressurization?

• A. To vent fuel fumes
• B. To monitor cabin temperature
• C. To regulate cabin pressure by venting air
• D. To supply air into the cabin

Answer: (C)

The outflow valve is the controlled vent that regulates cabin pressure by venting air from the pressurized cabin to the outside atmosphere. The cabin pressurization system uses a pressure controller that compares the sensed cabin pressure to the desired setting and then opens or closes the valve to maintain that target differential between inside and outside air. When the aircraft climbs and outside pressure drops, the valve opens more to vent additional air so the cabin doesn’t over-pressurize. When the airplane descends or needs to hold a higher cabin pressure, the valve closes more to retain air inside. This venting action keeps the cabin at a safe, comfortable pressure regardless of altitude. It’s not meant to vent fuel fumes, monitor temperature, or supply air into the cabin—the supply comes from the packs and bleed air, while the outflow valve only controls how much air leaves.