What are the three FMGC modes of operation?

The correct understanding of the FMGC (Flight Management and Guidance Computer) modes of operation includes dual, independent, and single modes.

In dual mode, both FMGCs operate together to manage the flight plan and data, providing redundancy and increased reliability. When both systems are functioning, they can cross-check each other, which ensures greater accuracy in navigation and flight management.

The independent mode permits one FMGC to operate separately from the other. This can be useful if one system encounters a fault, allowing the aircraft to continue flying with only one operational system while maintaining a certain level of functionality.

The single mode operates solely with one FMGC taking control while the other system is off or not engaged. This mode is less common and is typically only used during specific scenarios, such as when testing or if there is a need for minimal operation.

The other options presented do not represent the FMGC operational modes accurately. Understanding these three modes helps provide insights into redundancy and operational reliability in flight management systems within the A320 aircraft.