The PX Control Fault light comes on under which condition?

• A. Failure of both cabin pressure controllers
• B. Loss of hydraulic pressure
• C. Electrical fault in avionics bus
• D. Low cabin air temperature

Answer: (A)

This warning is tied to the cabin pressurization control system. The PX Control Fault light comes on when both cabin pressure controllers fail, because this system relies on two redundant controllers to maintain cabin altitude. If one controller fails, the other can still regulate, so the light doesn’t come on. The other scenarios—loss of hydraulic pressure, an electrical fault in the avionics bus, or low cabin air temperature—don’t indicate a complete loss of the dual-channel pressurization control, so they don’t trigger this specific warning. When this light appears, the aircraft would typically go into a degraded or alternate mode, and pilots follow the pressurization fault checklist to manage cabin pressure safely.