What does an illuminated FAULT light on the CABIN PRESS panel indicate and what would you do?

• A. Single sensor fault; read QRH and continue.
• B. Partial loss; switch to standby automatically.
• C. Outflow valve jam; reset
• D. Failure of both automatic pressure controllers has occurred. Pilot should take over with MAN control per the QRH.

Answer: (D)

When the FAULT light on the CABIN PRESS panel is illuminated, the system is signaling a loss of automatic control for cabin pressurization. In most aircraft, there are two automatic pressure controllers operating redundantly. If both fail, automatic regulation cannot be trusted, so the crew must take over and manage the cabin pressure manually.

The best course of action is to switch to manual control and follow the QRH procedures. This means the pilot takes custody of maintaining the desired cabin pressure by manually adjusting the system (such as controlling the outflow valve and monitoring cabin altitude and rate of change) to keep the cabin within safe limits throughout the flight. The reason this is the correct response is that the fault indicates a complete loss of automatic regulation, not a single sensor issue or a partial loss, and the standard procedure in the QRH is to hand-fly the pressurization until normal control can be restored.

Other scenarios described by the remaining options imply different faults or automatic actions that aren’t consistent with a FAULT indication for loss of both automatic controllers, so they don’t fit as the correct response.