The Use of Radar in Air Traffic Control3
At least two Air Traffic Controllers man each sector, one, the Procedural Controller, having the responsibility for decision-making with reference to priorities, separation standards and the safe, orderly and economic flow of air traffic; the other, the Radar Controller, having the responsibility of implementing those decisions by observing the air traffic on his radar screen.
The en route sector control radar screens have a range of 160 nautical miles - outside that range, procedural separation standards are maintained. Inside the area of radar coverage, however, all aircraft are continuously radar-identified and the radar separation standard of five miles may be employed at any time to solve such problems as aircraft wishing to change altitude or direction.
The en route Sector Controller's responsibility for inbound aircraft ends at 90 miles from destination where, in an AACC, he 'hands off' control and identification of the arriving aircraft to two Arrivals Controllers, the one with a flight progress board display of the arriving aircraft from all directions into an orderly sequence; the other, the Arrivals Radar Controller, using a 100-mile radius radar screen, being responsible for implementing the orderly sequence by the use of radar separation and speed control.
When each aircraft in the arriving sequence approaches 30 miles the Arrivals Radar Controller 'hands off' control and identification of the aircraft to the Approach Radar Controller who, again using the five-mile radar separation standard, integrates the arriving aircraft into an orderly approach sequence for landing. The Approach Radar Controller is a member of a three-man team manning the Approach/Departures Sector of the Area Approach Control Centre. This sector, comprising an area of responsibility of 30 nautical miles around the aerodrome, can best be described as the 'Terminal Area' where the movement of aircraft on radiating arrival and departure tracks causes congestion which, before the introduction of radar, would have meant comparatively long delays to air traffic movements.
The Approach Radar Controller using a 40-mile bright display radar screen is seated alongside a Departures Radar Controller using a similar screen so that each observes the other's traffic as well as his own. Departing aircraft are identified as soon as they become airborne. They normally receive a heading to fly determined by the Departures Controller in relation to the observed traffic on his radar screen and passed by the control tower to the pilot before his clearance for take-off.
The Approach Radar Controller and the Departures Radar Controller work in an atmosphere of close, face-to-face co-ordination, together with the third member of the sector team who keeps the flight progress strip data display up-to-date and who co-ordinates with the control tower the use of runways for departures and landings, and weather observations.
The objective of the Departures Controller is to clear his aircraft in a safe and orderly manner out of the terminal area and on to their particular en route tracks where they may be 'handed off' to the relevant en route Sector Controller. The duty of the Approach Controller is to marshal his arriving traffic into a safe and orderly arrival sequence and into a position where the pilot is established on a final approach landing aid or is lined up visually with the landing runway. When within 10 miles of the aerodrome, the arriving aircraft are then transferred to the control tower for a clearance to land.
The Terminal Area Radar Controllers (Departures and Approach) at Sydney and Melbourne, use 40-mile radius screens.
The long range radar aerial scans at five rpm, in other words, it constantly renews the radar picture provided to all controllers once every 12 seconds. However, increases in air traffic at Sydney and Melbourne particularly, brought the need for higher definition radar, capable of renewing its presentation at least once every 4 seconds. Accordingly the Department of Aviation installed high performance Terminal Approach Control Radars at Sydney and Melbourne (Tullamarine), and as the radar information could now be updated every 4 seconds, it was possible to reduce the radar separation standard to three miles. These radars serve the 40-mile radius terminal areas only.
The Department of Aviation has also implemented a further stage of its Radar Plan which is the installation at selected locations of Secondary Surveillance Radar which is not, as its name might suggest, a back-up or standby system for the primary radars already installed, although it may be used in conjunction with existing radars. SSR, as it is known, is a highly sophisticated system which depends for its operation upon the existence on an aircraft of a receiver/transmitter (transponder) which automatically responds to a recognised signal radiated from a ground station. Secondary Surveillance Radar when fully installed will provide the means by which an Air Traffic Controller will have automatically displayed to him information from an aircraft which he currently has to seek by radio communication. Such information as aircraft call-sign, altitude, speed and whether descending, climbing or cruising can be displayed automatically on a screen, together with the conventional radar 'blip'.
These facilities enable Air Traffic Control to serve Australia's highly sophisticated aviation industry with the highest standards of safety.
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