What happens if the active cabin pressure controller fails?

• A. The standby controller will automatically take over control.
• B. The emergency depress switch will be activated automatically.
• C. The outflow valve closes to hold cabin pressure.
• D. The system displays a caution and continues with manual override.

Answer: (A)

In a dual-channel cabin pressure control system, when the active controller fails, the standby controller automatically takes over to keep cabin pressure regulated. The two controllers continuously monitor the same pressure sensors and setpoints, so if the primary channel detects a fault, the backup is designed to seamlessly assume control without requiring crew action. This automatic switchover maintains safe altitude and pressure rates, minimizing disruption and maintaining passenger comfort and safety.

Reasons the other scenarios aren’t how this failure is handled: triggering an automatic emergency depress switch isn’t the standard response to a controller fault—the depressurization switch is used for intentional, rapid depressurization in certain emergencies, not as a automatic consequence of a controller fault. Closing the outflow valve to hold pressure would defeat the purpose of maintaining safe, controllable pressurization and isn’t how the failover logic operates. Finally, while a caution may appear to alert the crew, the system is designed to continue regulating via the standby controller automatically, rather than requiring manual override to maintain control.