How many automatic cabin pressure controllers are there?

• A. One
• B. Two
• C. Three
• D. Four

Answer: (B)

Redundancy is built into critical pressurization systems to keep cabin pressure safe at all times. Automatic cabin pressure controllers regulate the cabin by commanding the outflow valve to hold the target cabin pressure and smooth changes during climb and descent. There are two of these controllers—one active and one standby—so if the active unit or its sensors fail, the standby takes over automatically and maintains pressurization with little or no interruption. This arrangement prevents a single point of failure from compromising cabin pressure, which is why two controllers are standard.