Final answer:
In case of a generator bus failure or a generator failure with the bus tie open, critical displays like primary flight displays and essential navigation will remain operational, as they are powered by emergency or essential power systems.
Step-by-step explanation:
In the event of a generator bus failure or a generator failure with the bus tie open, certain displays will continue to function based on the aircraft's emergency or essential power systems. These systems are designed to maintain the operation of critical instruments and displays necessary for the safe operation of the aircraft. Typically, these would include primary flight displays (PFDs), essential navigation displays, and sometimes engine monitoring displays.
The exact displays that will remain operational depend on the aircraft design and the emergency power configuration. It is crucial for pilots to be familiar with their particular aircraft's emergency electrical systems to know which instruments they can rely upon in such a situation.