After the main generators, which power source is next in priority for AC power?

After the main generators, which power source is next in priority for AC power?

• A. External Power
• B. APU Generator
• C. Batteries
• D. Main Generators

Answer: (B)

Main generators supply the bulk of the aircraft’s AC power, so when they’re not available you need a reliable backup that can feed the AC bus without needing external power or the engines running. The auxiliary power unit’s generator fits that role because it can be started independently and immediately powers the AC system for essential avionics, lighting, and other loads during engine start or when one or more main generators are offline. External power is typically used on the ground when connected to a power source, and batteries (via the inverter) provide only limited, often DC-backed or short-duration AC power, not a full, continuous AC feed. So the APU generator is the next source in priority for AC power after the main generators.

Main generators supply the bulk of the aircraft’s AC power, so when they’re not available you need a reliable backup that can feed the AC bus without needing external power or the engines running. The auxiliary power unit’s generator fits that role because it can be started independently and immediately powers the AC system for essential avionics, lighting, and other loads during engine start or when one or more main generators are offline. External power is typically used on the ground when connected to a power source, and batteries (via the inverter) provide only limited, often DC-backed or short-duration AC power, not a full, continuous AC feed. So the APU generator is the next source in priority for AC power after the main generators.