What is the primary function of the outflow valve?

• A. Supply bleed air to the ECS
• B. Protect the pressure vessel from positive and negative pressure by venting air
• C. Seal the cabin
• D. Vent cabin to space

Answer: (B)

The outflow valve is part of the pressurization system and its job is to regulate cabin pressure by venting a controlled amount of cabin air overboard. It works with the cabin pressure controller to maintain the commanded cabin altitude and a safe differential between the cabin and outside air. As the aircraft climbs, air is supplied to the cabin, and the outflow valve opens enough to release air and keep the differential within limits; on descent, it closes more to let cabin pressure track ambient pressure. This venting protects the pressure vessel from being subjected to too much positive pressure or a loss of pressure beyond acceptable limits. It is not used to supply bleed air to the ECS, it does not seal the cabin, and it does not vent cabin air to space.