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Aviation History
1961
1961 - 1435.PDF
FLIGHT, 5 October 1961 Displays for Modern Radar Data Handling By D. W. G. BYATT, BSC, AinstP and F. W. KIME, AMIEE, AM Brit IRE * 539 THE air traffic control requirement has become increasinglycomplicated over the past decade, mainly because of thehigher traffic density and greater speed differential betweenthe types of aircraft to be handled. Until fairly recently Visual Flight Rules, by which a pilot relied on avoiding collisions byseeing and being seen in good weather, predominated. But in the airways and terminal areas the use of Instrument Flight Rulescoupled with direction from controllers using surveillance radar has allowed close aircraft separations to be maintained even underconditions of poor visibility. Normal procedure under these rules provides for advance notice of a flight to be derived from a flightplan submitted by the pilot before take-off. This plan will be correlated with other traffic movements and a specified route andheight agreed. At certain designated points the pilot will report his position, altitude and ETA at the next reporting point. On the ground, the controllers use information from flight plansand position reports to ensure that certain standardized separations are maintained between aircraft which are under control. Separa-tions are planned according to the available methods of navigation so that the acutal separation between aircraft can never becomeless than is considered safe. Reasonable allowance is made for navigational errors, for delays in air-to-ground and ground-to-airtransmissions, and for the expected movements of aircraft until the next reports are received. Clearly these factors can be reducedwhere aircraft are under radar surveillance and the controller can complement his procedural information with a dynamic display ofthe actual situation. The problem confronting the controller responsible for directingaircraft in this manner is most complex and exacting. He must build up and maintain a crystal clear mental picture of the situationin the sector for which he is responsible. This involves assimilating the flight data originally provided, up-dating it for each aircraftwhen position reports are received, predicting the future flight pattern and finally passing new instructions to the aircraft ifnecessary, to ensure that safe separation is maintained. The task is made more difficult because information to the controller becomesavailable in a variety of forms, is subject to different time delays and is of varying accuracy. Some data is presented on flightinformation strips, normally up-dated manually, while radar data comes from interpretation of a cathode-ray tube display and is up-dated at each aerial rotation. Turboprop and pure jet transports, with more rigid flight path requirements and speeds vastly inexcess of those of the slowest aircraft, introduce the need for anticipation of the future flight pattern over a much wider range,which greatly increases the complexity of the controller's task. It is therefore most important to relieve him as far as possible fromany work which is purely routine and to give him displays and computational aids which can be arranged to present only selecteddata and carry out conflict calculations. More time will then be available for making the decisions necessary to achieve the safe andunimpeded flow of air traffic. The basic information with which the controller must carry outhis task can be divided into two main groups and separate con- trollers, in close liaison, often use the different groups. There is * Marconi's Wireless Telegraph Co Ltd The new Marconi SD 1015 display unit and, above it, an example of the combined raw and synthetic display it can produce. Raw radar traces are each identified with three-character groups of letters and figures the procedural data based on flight plans and progress strips, andradar information—primary surveillance radar giving plan posi- tion data on all aircraft, or secondary radars giving instant identi-fication of aircraft fitted with transponders. Radar height, from height-finders or coded transponders may also be available. Additional information may come in from aircraft outside radarcover, via normal VHF and HF radio and from VDF position fixes. Less frequent but equally important in the controllers' workare reports of meteorological conditions, operational status of other airports, diversion arrangements and serviceability of navigationaids. It is essential that all this information should be assembled and displayed to the controller so that he may use it in the mosteffective way. Over the years the assistance given to controllers by means ofmechanical and electronic aids has gradually increased. As traffic has become more dense, the single radar controller has beenreplaced by several controllers, each covering a sector. Inter- display marks, controlled by a joystick, were introduced to facilitatehandover of an aircraft trace from one sector to the next. Video maps, showing the airways and reporting points, helped to orien-tate the aircraft patterns. The advances made in electronic com- puters and data-handling equipment in this and other fields,particularly as a result of vigorous development for the armed forces, made it possible for large-scale data processing to becarried out in real time, thus maintaining an accurate and up-to- date picture of an air situation. Data may then be arranged for display to particular controllersin the most effective manner. One method might be by primary radar display on which certain tracks would carry identification
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