What must be displayed when a sector has separation responsibility for an aircraft and a paired track exists?

When a sector has separation responsibility for an aircraft and a paired track exists, the Flight Data Block (FDB) must be displayed. The FDB contains critical information about the flight, including the flight number, type, altitude, and pertinent data related to the aircraft's route. This information is vital for controllers to maintain situational awareness and ensure safe separation between aircraft, especially when dealing with paired tracks, which may involve multiple aircraft moving through the same airspace.

The presence of the FDB facilitates quick reference and verification of the aircraft's details, which is essential for effective separation management within an air traffic control environment. It allows controllers to visualize the traffic situation clearly, ensuring that they can take timely actions to maintain safety, particularly in busy or complex airspace.

While other options like the Aircraft Flight Plan, Separation Assurance Indicator, and Flight Status Update provide useful information, they do not replace the necessity of having the FDB displayed for operational responsibilities related to separation assurance. The FDB specifically integrates all the information needed for controllers to perform their role effectively in monitoring and managing air traffic.