Which of the following is true about the number of automatic cabin pressure controllers?

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

Answer: (B)

Two automatic cabin pressure controllers are provided to keep pressurization safe and reliable. Each controller watches cabin altitude and the rate of change, then commands the outflow valve to hold the cabin at the selected pressure. With two channels, the system can cross-check and share control, so if one controller or its sensor data faults, the other continues to regulate automatically without crew action. This redundancy is why two is the correct answer.

Having just one would leave the system vulnerable to a controller or sensor failure, and having three or four isn’t typical for this function and adds unnecessary complexity.