The PX Control Fault light indicates a failure of which components?

• A. Cabin pressure controllers
• B. Bleed air valve
• C. Avionics fan
• D. Temperature sensors

Answer: (A)

The PX control fault light points to an issue in the system that regulates cabin pressure. The cabin pressure controller is the device that keeps the cabin at the desired pressure by comparing the sensed cabin pressure with the setpoint and then commanding the outflow valve to adjust as needed. When that control loop detects a fault, it lights up the PX control fault indicator to warn that regulation isn’t functioning properly.

If the light came on, it would not typically indicate a problem with the bleed air valve itself (which is a valve in the air supply path), or with avionics cooling (avionics fan), or with cabin temperature sensors. Those components relate to different system functions (air supply routing, electronics cooling, and temperature monitoring, respectively). The fault being tied to control logic and regulation fits the cabin pressure controller, making it the best answer.