How many CPCs are installed on the aircraft?

How many CPCs are installed on the aircraft?

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

Answer: (A)

Redundancy is the key idea here. The cabin pressurization control is a critical function, so it’s designed with two Cabin Pressure Controllers to ensure continuous, safe operation even if one unit fails. Both CPCs monitor the same inputs—cabin differential pressure, the crew’s altitude/cabin pressure setpoint, and the air inside the cabin—and they work with the outflow valve to hold the desired cabin pressure. Typically one CPC acts as the master, actively commanding the outflow valve, while the other serves as a standby/monitor and can take over if a fault is detected. This dual-channel arrangement avoids a single point of failure and keeps the cabin pressurized within safe limits. Having more than two isn’t needed for this redundancy level, and a single CPC would not provide the same safety margin.

Redundancy is the key idea here. The cabin pressurization control is a critical function, so it’s designed with two Cabin Pressure Controllers to ensure continuous, safe operation even if one unit fails. Both CPCs monitor the same inputs—cabin differential pressure, the crew’s altitude/cabin pressure setpoint, and the air inside the cabin—and they work with the outflow valve to hold the desired cabin pressure. Typically one CPC acts as the master, actively commanding the outflow valve, while the other serves as a standby/monitor and can take over if a fault is detected. This dual-channel arrangement avoids a single point of failure and keeps the cabin pressurized within safe limits. Having more than two isn’t needed for this redundancy level, and a single CPC would not provide the same safety margin.