Which items are powered from the DC Emergency Bus?

• A. Engine and APU fire extinguishers; fuel and hydraulic shutoff valves (both a and b)
• B. Engine fire extinguishers only
• C. Fuel shutoff valves only
• D. APU fire extinguishers only

Answer: (A)

In an electrical emergency, the DC Emergency Bus provides power to systems that must operate even when the main power is down. It powers the engine and APU fire extinguishers, ensuring they can be discharged to suppress fires in both engines and the APU without relying on the normal electrical system. It also powers the fuel and hydraulic shutoff valves, enabling rapid isolation of fuel and hydraulic supply to the affected units. Because both fire suppression and isolation need to function reliably in an emergency, these items are designed to be powered by the DC Emergency Bus. That’s why the correct choice includes both engine and APU fire extinguishers and both fuel and hydraulic shutoff valves.