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Aviation History
1959
1959 - 0521.PDF
256 FLIGHT, 20 February 1959 FLYING Al DS . . . Interconsole marking and tracking on a Marconi system. Console 1, key operated to show own symbol on own console; console 2, key operated to show symbol on own console; console 3, keys operated to show own symbol on own console and transmit own symbol to No. 2; console 4, keys operated to show own symbol on own console and to transmit own symbol to No. 2 JOYSTICK, RANGE AND BEARING CONTROLS FOB LEADING LINE to fix the position of an aircraft with a D.F. triangulation systemin relation to a map electronically incorporated in the display and to make an accurate assessment of the required track and distanceto reach a given point. This affords a simple method of identifying and directing aircraft.Such a system is already used by the R6gie des Voies Aeriennes in Belgium with back-projection onto a ground-glass map screenof C.R.D.F. traces (Standard Telephones and Cables PVT.l) and surveillance radar. Both fixing and directing functions must relyon the communications channel and heavy traffic might saturate the system;, although this consideration applies equally to anyorganization depending on surveillance radar. The identification process could be made less cumbersome anda more comprehensive picture of the situation produced by in- tegrating flight progress information with radar surveillance. Theradar picture itself can be improved by extracting velocity infor- mation from it and displaying this together with flight-planinformation on another screen. Radar will provide a continuous series of position reports fromwhich a skilled operator can make an assessment of speed and direction of movement. The identification problem can be greatlysimplified by advance warning of the arrival of an aircraft in the scanned area and by a knowledge of its intentions, whether suchinformation is derived from the radar surveillance in a neighbour- ing area or from flight plans, the essence of which is featured onthe flight progress strip. Radar and non-radar information can be combined in a data store. The object is to provide all available information, without anyirrelevant signals, to the executive controllers. In the Marconi system, which is typical, it is foreseen that one group of operatorswill identify and track aircraft and be able to transfer the resultant information into a store where information from other sourceswill be added. A series of symbols can therefore be superimposed on the radar screen and steered by means of a joystick control tolie over an aircraft echo. In order to allow cross-referencing between operators, the symbol and its position on the tube facecan be electronically repeated on another tube so that one operator can position a symbol over an echo, press a switch and make thesame symbol appear round the same echo on another screen. The next stage is to derive velocity information from the radardisplay by making a symbol follow an echo across the screen. Using a fixed-coil display, there are two methods by which thiscan be done. Firstly, the symbol can be given a speed and direc- tion by joystick control so that symbol and echo move alongtogether. The velocity can be judged "by eye" so that the symbol follows the aircraft until it changes heading or speed. This kindof tracking system is called rate-aided and has been produced by Marconi, Decca Radar and Cossor. With additional equipment itis possible to lock the symbol electronically to the echo so that they will remain synchronized wherever the echo moves. This obviouslyhas its advantages because the operator no longer has to check that rate-aided symbol and echo are staying together; but if thetracks of two echoes cross, the electronic following system will be confused and circuits to overcome this difficulty are complex. Theautomatic tracking system is generally called lock-follow or auto- follow. A variety of symbols can be provided for either rate-aided or automatic following and it is estimated that a single operator caneffectively supervise about a dozen different aircraft in this way. A group of operators would in practice be monitored by a super-visor who allocated targets and constantly reviewed the overall situation. From this radar information-gathering stage the track-ing symbols and their velocities could be electronically transmitted to other tubes for direct use in progress control, or they could befed into an electronic store with an identifying number. The store is in effect the second block of the overall radar control systemand, in addition to receiving track data and identification numbers from the surveillance radar section, it would accept informationfrom such sources as radar height finders, radar transponder beacons carried in aircraft, and flight-plan information derivedfrom the conventional land-line and radio sources. In all probability the data stores used in traffic control systemswill be based on binary digital inputs. The analogue devices using voltages or uni-selectors would become uneconomical if morethan 30 tracks were involved because of the bulk and cost of the mechanisms and because of difficulties in the input and outputsections. About 160 "bits" of binary information are required in order to store details of route, height, course, speed, call-sign,change of height and other relevant flight-plan data. A store based on a ferrite matrix is favoured by Marconi, while magnetic drumsystems are being used in the Dutch SATCO and the American Data-processing Control. The store of the Marconi civil aviation data-handling systemshown at Farnborough last year has a capacity for up to 160 tracks. Identified tracks are passed from the fixed-coil displays of theinformation-gathering section into the store which can automatic- ally compute the co-ordinate velocities. Present-position infor-mation is kept up-to-date by continual rate-aided tracking. Addi- tional information from non-radar sources may be added to thestore by manipulating keyboards. Further channels could be pro- vided for air-to-ground data-link. All the information can beextracted from the store in a form suitable for use in computers designed to assist controllers in co-ordinating traffic. The third block in the Marconi system is the executive elementof the control organization and the equipment consists of two basic displays. The first is a completely synthetic radar display ona cathode-ray tube which will present only computed information, probably orientated in a video map. Two basic variations ofdisplay can be selected by switches. The first is a so-called "tadpole" display in which a bright dot shows the position of anaircraft and a "tail" of lower brilliance indicates its speed and direction. The second is the symbol display in which the presentposition of an aircraft is shown by a symbol accompanied by letters, figures and signs giving the track-identification, and heightrepresented by two figures for thousands of feet and a dot for 500ft. A "tadpole" in this case will show whether the aircraft isclimbing or descending and a bar indicates whether or not the information has been derived from radar. It is obviously importantthat the quality of the information shown on the tube should be known. Since all information used at this executive stage is being drawnfrom a store with ability to make computations, the controller can "advance" the display up to 7i min into the future to gain an ideaof what the situation will be if all aircraft maintain their present
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