What powers the DC Emergency Bus and how is it powered?

What powers the DC Emergency Bus and how is it powered?

• A. APU Direct Battery Bus and DC Battery Bus
• B. Engine Fire Extinguishers
• C. Fuel SOV
• D. Hydraulic SOV

Answer: (A)

During an electrical abnormality, the DC Emergency Bus remains powered to keep essential cockpit systems running. It is fed from two dedicated DC sources: the APU Direct Battery Bus and the DC Battery Bus. When the APU is operating, power can flow from the APU Direct Battery Bus to the DC Emergency Bus, maintaining critical instruments and avionics even if main generators are unavailable. If the APU isn’t providing power, the DC Battery Bus can supply the emergency bus from the aircraft’s battery, giving a last-resort source of power to those essential systems. The other options aren’t power sources at all—engine fire extinguishers are a fire-suppression system, while Fuel SOV and Hydraulic SOV are valves for their respective systems, not electrical power sources.

During an electrical abnormality, the DC Emergency Bus remains powered to keep essential cockpit systems running. It is fed from two dedicated DC sources: the APU Direct Battery Bus and the DC Battery Bus. When the APU is operating, power can flow from the APU Direct Battery Bus to the DC Emergency Bus, maintaining critical instruments and avionics even if main generators are unavailable. If the APU isn’t providing power, the DC Battery Bus can supply the emergency bus from the aircraft’s battery, giving a last-resort source of power to those essential systems. The other options aren’t power sources at all—engine fire extinguishers are a fire-suppression system, while Fuel SOV and Hydraulic SOV are valves for their respective systems, not electrical power sources.