What is the function of the EXT PWR switch?

The function of the EXT PWR switch is to provide power to the left essential (LH ESS) bus. When activated, the EXT PWR switch allows the aircraft’s essential electrical systems to draw power from an external source, rather than relying on the onboard battery or generators. This capability is especially useful during pre-flight preparations or after landing when the aircraft requires power for systems but does not need to run the engines.

The ability to connect to an external power source helps conserve battery life and ensures that critical systems remain operational without the need for the aircraft’s engines to be running. This feature is vital for maintaining the functionality of essential systems during ground operations.

The other options do not serve the same purpose. For instance, while transferring generator power to the left bus or stopping all external power sources may be functions of different switches or systems, they do not reflect the specific role of the EXT PWR switch in delivering power to the LH ESS bus. Likewise, disconnecting the battery from the system pertains to a different operation altogether that deals with the isolation of the battery rather than its connection or the provision of power.