Which AC Bus powers the APU Battery Charger?

Which AC Bus powers the APU Battery Charger?

• A. AC Bus 1
• B. AC Bus 2
• C. AC Service Bus
• D. Essential Bus

Answer: (C)

The APU Battery Charger is powered by the AC Service Bus. This bus is intended to carry loads that aren’t critical to flight control, so charging the APU battery doesn’t compete with power for essential systems. When any AC power source is available—external power or the APU providing power—the AC Service Bus is energized and can supply the charger, keeping the APU battery charged for a reliable APU start. If the charger were tied directly to the primary AC buses or the Essential Bus, charging could interfere with or be affected by loads tied to those buses, especially during power transfers or faults. The Service Bus setup isolates the charging path from critical flight systems while still ensuring the APU battery remains charged whenever power is available.

The APU Battery Charger is powered by the AC Service Bus. This bus is intended to carry loads that aren’t critical to flight control, so charging the APU battery doesn’t compete with power for essential systems. When any AC power source is available—external power or the APU providing power—the AC Service Bus is energized and can supply the charger, keeping the APU battery charged for a reliable APU start. If the charger were tied directly to the primary AC buses or the Essential Bus, charging could interfere with or be affected by loads tied to those buses, especially during power transfers or faults. The Service Bus setup isolates the charging path from critical flight systems while still ensuring the APU battery remains charged whenever power is available.