Procedural Control
General
The general principles of air traffic control are the same regardless of whether procedural or surveillance methods are used (i.e. the controller monitors the traffic situations, detects and solves conflicts by providing separation, and ensures orderly flow of the air traffic). The difference lies in the way situational awareness is built and updated (by pilot reports, estimates and visual observation), the separation minima themselves (as described in ICAO Doc 4444, Chapter 5) and the support tools (flight strips instead of a situation display).
Where procedural control is employed, separation is achieved through the segregation of airspace, either vertically or laterally. Due to the lack of assured surveillence within a Control Zone, that zone may be classed as procedural - where separation is provided by positive time or distance control. There are four types of procedural separation - lateral, longitudinal, vertical and visual.
Typical Applications
Typical applications of procedural control include:
- In airspace where surveillance cover is not available (e.g. oceanic airspace or sparsely populated areas)
- In terminal movement areas (TMAs) if the traffic levels are such that they do not warrant the installation and maintenance of a surveillance system
- In aerodrome control zones (CTRs), especially if the traffic density is relatively low and the aerodrome layout is not complex (e.g. only one runway, one apron and a few taxiways)
- Backup solution in case of complete failure of all surveillance-based systems