Which items are powered by the DC EMER BUS?

• A. Cabin lighting and galley power
• B. Fuel pumps and hydraulic pumps
• C. Engine and APU fire extinguishers and hydraulic and fuel shutoff valves
• D. Primary flight displays and navigation systems

Answer: (C)

The DC emergency bus is designed to keep essential safety functions alive when normal power is lost. It supplies power to systems that must operate to protect the aircraft and its occupants in an emergency, even when most other systems are down.

The items that are powered by this bus include the engine and APU fire extinguishing systems and the hydraulic and fuel shutoff valves. These functions are critical for safety: the fire extinguishers can be deployed to suppress any engine or APU fire, and the shutoff valves allow isolation of fuel and hydraulic sources to prevent further damage or fuel leaks.

Other systems, like cabin lighting and galley power, or primary flight displays and navigation, are important but not prioritized for emergency power on the DC emergency bus in the same way, and fuel or hydraulic pumps are typically managed differently in an emergency power scenario.