What does the AC ESS XFER switch light signify?

The AC ESS XFER switch light indicates that the transfer of power is automatic during an AC BUS failure. This means that when there is a loss of power from the primary AC bus, the electrical system is designed to automatically switch to an alternative power source to ensure continuous power supply to essential systems. This feature is critical in maintaining operations and ensuring safety, as it minimizes the risk of power interruption during flight.

In contrast, other options represent situations that do not directly apply to the function of the AC ESS XFER switch light. For instance, manual overrides or indications of failure of the primary power source, while important aspects of electrical system management, are not represented by the behavior signified by the AC ESS XFER switch light. The automatic transfer function is a specific and essential characteristic that highlights system reliability in critical scenarios.