Which element of the pressurisation system moves to regulate cabin pressure?

• A. Outflow valves
• B. Bleed air valve
• C. Safety valve
• D. Pressure relief valve

Answer: (A)

Regulating cabin pressure is achieved by controlling how much conditioned air leaves the cabin. The outflow valve is the component that moves to vary the amount of air escaping from the cabin to the outside. The pressurization system uses a controller to maintain the desired cabin pressure by adjusting the outflow valve: if the cabin tends to rise in pressure, the valve opens to vent more air; if the pressure is lower than desired, it closes to retain more air. The bleed air valve is involved in delivering air to the conditioning packs, not in regulating cabin pressure directly. Safety and relief valves act as protective devices that vent air only if overpressure occurs, rather than actively controlling normal cabin pressure.