What is the purpose of the outflow valve?

• A. Maintains cabin altitude
• B. Increases cabin pressure
• C. Heats cabin air
• D. Filters cabin air

Answer: (A)

The outflow valve’s job is to regulate cabin pressure by venting cabin air to the outside. In a pressurized aircraft, air is supplied to the cabin and the outflow valve controls how much of that air escapes. By adjusting the amount vented, the system keeps the cabin pressure at the desired level, which translates to a safe cabin altitude for passengers and crew. If pressure tends to rise, the valve opens more to vent air; if it tends to drop, it closes to retain air.

This valve doesn’t heat cabin air—that’s done by the environmental control system’s packs—and it doesn’t filter cabin air. It also doesn’t increase cabin pressure; it lowers or maintains it to achieve the set cabin altitude.