Which valve is responsible for maintaining cabin pressurization by regulating outflow?

• A. Outflow valve
• B. Ram air valve
• C. Safety valve
• D. Vent valve

Answer: (A)

Cabin pressurization is controlled by regulating how much air leaves the cabin. The outflow valve is the primary device that modulates this exhaust path. It’s controlled by the pressurization system to hold the selected cabin pressure, adjusting its opening to maintain the desired differential between inside and outside air. When the airplane climbs, the differential tends to increase, so the valve opens more to let more air escape and keep the cabin pressure at the set value. If the valve narrows, less air leaves and the cabin pressure rises toward the target.

The ram air valve, by contrast, provides outside air for ventilation or cooling when needed, such as for pack operation or certain abnormal conditions; it does not regulate the cabin pressure under normal operation. The safety valve is a relief device that opens only if the differential pressure would become unsafe, preventing structural damage—not for normal regulation. Vent valves may handle other ventilation duties, but they do not manage the primary cabin pressure in the same way as the outflow valve.