Which bus is supplied with power when the GPU is selected and the batteries are OFF?

Which bus is supplied with power when the GPU is selected and the batteries are OFF?

• A. Ground service bus
• B. Main bus
• C. Essential bus
• D. Bus tie bus

Answer: (A)

External power from the GPU powers the Ground Service Bus when the batteries are OFF. This bus is specifically designed to be energized on the ground to support ground operations and preflight setup, providing essential cockpit lighting and avionics without drawing on the aircraft’s batteries. With batteries not supplying power, the main and essential buses stay unpowered unless their sources are active, and the bus tie bus serves as a link, not a power source. So the Ground Service Bus is the one fed by the external power under this condition.

External power from the GPU powers the Ground Service Bus when the batteries are OFF. This bus is specifically designed to be energized on the ground to support ground operations and preflight setup, providing essential cockpit lighting and avionics without drawing on the aircraft’s batteries. With batteries not supplying power, the main and essential buses stay unpowered unless their sources are active, and the bus tie bus serves as a link, not a power source. So the Ground Service Bus is the one fed by the external power under this condition.