Which item is not part of the AC bus power priority?

• A. Onside Generator
• B. APU Generator
• C. External Power
• D. Main Battery Direct

Answer: (D)

AC bus power priority defines the order in which sources feed the aircraft’s AC bus to keep essential systems powered. The sources that can directly feed the AC bus are external power, the APU generator, and engine-driven generators. These are all AC sources that the system uses in a defined sequence: external power first when available, then the APU generator, and then the engine generators.

The main battery direct path isn’t part of this AC bus priority because the battery provides DC power. To supply AC loads from the battery, power must first go through an inverter to convert DC to AC. Since the priority is about directly feeding the AC bus from AC sources, the main battery direct path isn’t included in that scheme.