What happens if the CPC microprocessor fails?

• A. Autopilot disconnects automatically.
• B. The cabin air conditioning will shut down completely.
• C. The flight data recorder will stop recording.
• D. The oxygen masks will not drop automatically and the Seatbelt and No Smoking signs will not illuminate.

Answer: (D)

The CPC (cabin pressure controller) microprocessor coordinates the cabin environment and safety indicators, including automatic oxygen deployment and the illumination of safety signs. When it fails, the automatic actions that rely on it don’t operate. Oxygen masks dropping automatically and the seatbelt and No Smoking signs illuminating are controlled by signals from this system, so a CPC failure means those functions won’t occur automatically.

Other systems operate independently: autopilot behavior is managed by flight control computers, cabin air conditioning has its own environmental control logic, and the flight data recorder logs data separately. So the immediate and observable effect tied to a CPC fault is the loss of automatic oxygen mask deployment and sign illumination.