Thus, the proximity relationships of aircraft with some key waypoints (e.g., intersection points, metering fix) in the sector severely affect the complexity of air traffic situations.
Specifically, Flight 1 is approaching sector S3 from sector S1; Flight 2 flies from sector S3 to sector S1 and is flying away from the metering fix, whose reference distance [mathematical expression not reproducible] is set as 15 km.
Among all air traffic situations faced by the controller, in addition to the between-aircraft relationships, there are also relationships between aircraft and airspace structure (e.g., an aircraft is approaching a metering fix or deviating from the authorized airway).
