Which buses will be powered when APU generators supply aircraft power?

When the Auxiliary Power Unit (APU) generators are supplying power to the aircraft, the correct choice indicates that all buses except the monitor buses are powered. This is due to the role of the APU in providing electrical power to the aircraft's systems while on the ground or during specific flight conditions.

The reason this is the right answer is that the APU is designed to serve the aircraft's critical and non-critical systems, supplying energy to all necessary electrical buses, which include essential buses that serve vital functions, as well as other buses that support non-essential equipment. However, the monitor buses, which are typically associated with system checks and diagnostics, may not receive power from the APU generators because they are not critical for operation while the APU is in use.

In contrast, the other options do not cover the full scope of power distribution effectively. If only essential buses were powered, it would limit the functionality of many non-critical systems that may still require power for serviceability and convenience. Saying only the main bus is powered does not reflect the comprehensive capability of the APU in providing necessary energy across the aircraft's system architecture. Lastly, including battery buses in the power allocation by the APU would typically not be accurate in standard operations, as the