What should be retained until the aircraft has exited the sector or delegated airspace?

Retaining the data block until all potential conflicts have been resolved is crucial for maintaining situational awareness and ensuring safe separation between aircraft. The data block is a visual representation on the radar display that contains critical information about an aircraft, such as its altitude, flight number, and intended route. By keeping this information available until the aircraft completely exits the sector or delegated airspace, controllers can effectively monitor and manage any potential encounters with other aircraft. This helps alleviate any conflicts that might arise, allowing for timely interventions if necessary to maintain safety.

Other aspects, such as flight plan data and communication logs, although important for operational purposes, do not directly impact immediate in-flight safety with respect to monitoring and conflict resolution. Landing clearance, on the other hand, pertains to the aircraft's approach and landing phase, rather than its ongoing operations within the airspace. In a radar environment, the focus is primarily on the current position and movement of aircraft, making the retention of the data block essential for real-time decision-making.