In descending order, what is the priority of electrical power?

The correct answer reflects the established protocol for prioritizing power sources on the A320. The method for prioritizing electrical power is crucial for ensuring a reliable and continuous electrical supply during various phases of flight.

The onside engine generator takes precedence as it is directly linked to the aircraft's propulsion system, ensuring that reliable power is generated while the aircraft is in operation. Next in line is external power, which is typically available when the aircraft is on the ground and allows for significant electrical load handling without relying on internal power sources. Following that is the auxiliary power unit (APU), which provides electrical power when the engines are not running or when additional power is needed, such as while on the ground. Finally, the remaining engine generator is considered last, as it becomes relevant primarily when there is a need to utilize both engines due to high demand or failure of other power sources.

This prioritization is designed to maintain operational efficiency and safety, ensuring that the most reliable and powerful sources of electricity are used first, especially in critical situations. The other options either place these sources in the incorrect order or overlook the importance of the engine generator as the primary source of power during flight.