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Aviation History
1958
1958 - 0653.PDF
16 May 1958 669 careful and often protracted and painstaking evaluation under representative conditions. Universal practices and universal A.T.C. systems, desirable as they are, may have to be subjugated to local : needs and local budgets; but new aids are urgent now. By the end of this year the first of the big jets will have started operations on the world's busiest air routes over North America, the North Atlantic and Europe. Because air traffic control today still relies in the main upon position reporting from the cockpit for the separation of traffic, accurate navigation assumes continually greater importance. B.OAC's deputy flight services manager, E. W. Pike, has said that "today the separation problem is completely dominating the navigational problem." The accuracy demanded of position reports on Europe's congested airways system is conditioned by the need to crowd more and more aircraft into the defined air routes. The airways cannot be much further extended without severely hampering military, private and manufacturer's test flying. New U.K. airways introduced to serve the new Gatwick terminal have already swallowed much of the free space in south-east England. The critical separation problem is still the most difficult to resolve. To the vertical separation afforded by the four-segment quadrantal rule can be added lateral separations of aircraft tracks and longitudinal separations in distance or in time. Although primary reliance is placed upon vertical separation, position and altimeter instrument errors and the use of mean barometric pres- sure settings can result in wide variations of altitude—much in excess of 500ft quadrantal spacings—even with aircraft employing a height lock on the autopilot. Tests have shown variations of 1,400ft on a modern B.O.A.C. aircraft with known or corrected instrument errors. Yet to employ wider vertical separations is to impose uneconomic restrictions upon operations. The penalties of flying off the flight-planned altitude in a big jet (where the fuel consumption can be equivalent to the weight of one passenger used up per minute) can be 2 per cent up to 4,000ft off flight-plan and 9 per cent up to 9,000ft-;—a figure approaching the total payload. Over the North Atlantic, saturation has been reached on separa- tion by vertical displacement alone, and extended lateral and longi- tudinal separations of 120 miles have been adopted. With 180 aircraft over the Atlantic at the same time at peak periods little arithmetic is needed to indicate the enormity of the problem. The only way to avoid delays is to reduce separation, and the way to do this is to improve the accuracy of position reporting with a long-range area-coverage navigation aid. The' early promise of Dectra as such an aid has been borne out by tests over the Atlantic during the past ten months and there seems good hope that a sophisticated "belt and braces" system such as Decca/Dectra/ Doppler will provide a reliable and accurate answer to the position- reporting problem. The time is rapidly approaching when air traffic control and navigation can no longer be regarded as separate problems. But such close accuracy, 1,500 miles out over the Atlantic, is not to be achieved overnight, and meanwhile A.T.C. officers will still apply their own factors to pilot's position reports. The North Atlantic may well become one of the world's most closely regulated traffic areas and the halcyon days of jet stream joy riding may soon be passed. One thing is certain; the principle of "see and be seen" trans- poses a quite unacceptable burden of air traffic responsibility from controller to pilot. The problem is not one of cockpit visibility, but of cockpit workload. Some recent deliberate experiments in the U.S.A. with radar-monitored collision courses and an analysis of 50 air-to-air collisions has provided frightening evidence of the uselessness of expecting pilots to maintain separations by keeping a look-out from their cockpit windows. Collision warning devices, now a stage nearer reality after the technical setbacks of a year ago, could provide a useful safeguard particularly against random intruders into airways, but are no substitute for full control. Inevitably, the progress of control techniques depends upon the development of radar, of television presentation of information, and of computer assistance to allow the controller to concentrate quickly and simply on making necessary decisions—and nothing else. In the same way, the effectiveness of ground control relies upon improved airborne navigational aids (for better position fix- ing) and development of position reporting for aircraft by semi- automatic data link, or by airborne teleprinter. The day of the small bright P.P.I. tube in a darkened control room is passing; the strain is too great and the information is required by too many people at once. Larger screens with coded, synthetic-display presentation can be studied effectively in better lit rooms. If there is a pattern emerging for the organization of air traffic control centres, it is for the use of more and better radar, with overall monitoring of the complete airways system (and telephone or microwave link between adjacent radars and the controllers) three dimensional display, automatic ground-to-air communication, and electronic aids to replace the written-out tally system of passing flight progress reports. . One of the more ambitious efforts on these lines is that of the Dutch firm Hollandse Signaal Apparaten of Hengelo who last year Computers will replace manual processing in future traffic control centres. Above is the computer of the R.R.E. defence system at Malvern while below is the memory drum and wind-data input panel at SATCO, which can store 1J000 flight plans.
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