If the bus tie is set to open, which annunciator will illuminate?

When the bus tie is set to open, the amber BUS TIE annunciator will illuminate. This is because the amber color is typically used to indicate a caution or advisory condition in aircraft systems. The opening of the bus tie signifies that the two electrical buses are isolated from each other, which can affect the distribution of electrical power within the aircraft.

The illumination of the amber BUS TIE indicates to the crew that there is a potential issue with the electrical power distribution that needs attention, as certain systems may not be powered as expected. This visual alert serves as an important indicator that the crew should monitor the electrical system status.

In contrast, the green BUS TIE indicator usually represents that the bus tie is closed and functioning normally, while a red BUS TIE would signify a more serious fault or emergency situation requiring immediate action. The option stating that no annunciator will illuminate does not reflect the operational logic of the system and would not provide the necessary alert for the crew regarding the bus tie being open.