How does a narrowbody control cabin pressure and what component regulates the differential pressure?

• A. The Environmental Control System uses an outflow valve to regulate cabin air; a pressure controller maintains the set differential pressure.
• B. Cabin pressure is controlled solely by the packs.
• C. An automatic cabin door regulates cabin pressure.
• D. Cabin pressure is controlled by the autopilot and a separate valve.

Answer: (A)

Cabin pressure is kept by the Environmental Control System, which precisely balances how much air is in the cabin with how much air is allowed to escape. The key regulator is the outflow valve, which opens or closes to control the rate at which cabin air leaves. A pressure controller monitors the cabin and differential pressure and commands the outflow valve to maintain the preset differential pressure (the difference between cabin and outside pressure). The packs provide the conditioned air, but they don’t regulate the delta-P themselves. An automatic cabin door or the autopilot aren’t involved in pressurization regulation.