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Aviation History
1959
1959 - 0266.PDF
23 January 1959 Britain's Navaid Proposal %i_::.. .„ DECCA Mk 10 ADVOCATED AS STANDARD SHORT-RANGE AID 121 AS a preliminary to next month's critical I.C.A.O. meeting in l\ Montreal to decide the future short-range navigation aid, L Jk. the M.T.C.A. is giving a series of demonstrations in a Comet 2E of the Decca Navigator Mk 10 which is the British candidate for standardization. The Americans have already held a symposium on Vortac, to which they feel committed. The tactics they have for some time applied in furthering their aid have come under fire in the British Press, and Flight commented on the subject last week (p. 113). In next week's issue we hope to include a report on one of the demonstration flights. The M.T.C.A. has prepared a detailed exposition of United Kingdom policy on the navigation-aid situation, giving precise reasons for British support for Decca in crowded traffic areas. The summary which we print below stresses the strong reasons behind this choice. It should be remembered that the Ministry base their support on the Mk 10 receiver, which is a great advance on earlier equipment. They also stress the development and expansion potential of Decca and note the limited capacity and much greater costs of Vortac. Tables, reprinted overleaf, and charts (some sections of which we also reproduce) strongly emphasize the arguments put forward. Also revealed by the M.T.C.A. is the existence of the Decca autopilot coupling systems, one of which is now being tested in flight, and the proposed H.F. digital data link system for automatic air-to-ground notification of aircraft-position. . The Ministry's Views In effect, the M.T.C.A.'s statement summarizes many of the arguments already advanced in Working Papers which the United Kingdom has submitted for the consideration of the Montreal meeting. It is hoped that these views will "Help States to under- stand why the U.K. is convinced that many of the problems of air traffic control could be solved by the use of a high-accuracy, hyperbolic navigational system." Use of such an aid was advo- cated by the U.K. delegation to the Special Technical (COT) Division convened by the Provisional I.C.A.O. Interim Council in November 1946. Since that date (continues the M.T.C.A.) continuing study of traffic control problems, together with practical evaluation of various navigational systems, has served only to strengthen their conviction that other States will, in time, reach the same conclusion. Nevertheless, the U.K. recognizes that in many areas of the world the present I.C.A.O. standard aid, VOR, could provide all the guidance necessary for the navigation and control of aircraft for a number of years to come. It will support the installation or retention of VOR wherever it can be shown that it meets the operational requirement. It is equally clear that in some busy terminal areas, and in those parts of the world where the natural flow of aircraft between a large number of airports would produce a complex, conflicting pattern of airways, the rigidity of the point-source aid [i.e., VOR] restricts the capability of the traffic control system to provide the number of flight-paths necessary to achieve an optimum traffic-flow. For this reason, States are forced to introduce inflexible procedures, unwieldy patterns and circuitous routings which inevitably require additional controlled airspace and affect the balance sheets of airlines. Moreover, the errors of VOR are such that any State wishing to conserve airspace or to introduce parallel flight-paths must adopt a close spacing between the facilities if the dimensions of the controlled airspace are to be kept within reasonable limits. In some high-density areas the problems of siting, frequency allocation and cockpit workload may, in fact, make it impossible to achieve the ideal deployment, with the result that there will be a serious encroachment on the upper-airspace requirements of the military authorities. It is, of course, possible to increase the capacity of a single airway by reducing the longitudinal separation. The U.K. was one of the first countries to do this on a regular basis and the con- tinued use of radar has enabled A.T.C. to handle a much larger volume of traffic than would have been possible using procedural separation standards. The introduction of equipment, such as DME, which will enable pilots to keep a close check on progress along track will undoubtedly lighten the load on radar controllers, but it is unlikely to increase the capacity of a radar-monitored airway to an extent which would justify the installation of DME on these grounds alone. The U.K. fears that a decision to standardize DMET (the DME element of Tacan which, together with VOR, forms Vortac) at the Montreal meeting will lead States so far into the web of the rho theta point-source concept that it will become almost impossible to disentangle. States must face the possibility that the failure of VOR/DMET to handle the traffic might lead to a demand for the more accurate azimuth guidance of Tacan (a wholly American military development for tactical air navigation) and for an ever-increasing reliance upon radar controllers to overcome the basic deficiencies of the point-source system. The U.K. believes that the present unsatisfactory state of affairs has come about because some States have placed too great an emphasis on the need for a common civil /military navigational system. This has tended to override the true operational require- ments of world-wide civil aviation. These requirements are today dictated in the main by A.T.C. considerations, particularly in high-density areas where civil airspace is limited, and by the more stringent operating characteristics of the turbine-powered aircraft now entering service in increasing numbers. New aircraft have brought special requirements in control and navigation which the radio-aid must satisfy. Turbine-powered aircraft operate most efficiently at high altitudes and at high speeds. Their engine characteristics are such that efficiency is reduced, and fuel consumption increased, when A.T.C. is constrained to restrict their freedom in the vertical plane. For airlines, the economic implications of such restrictions can be severe. It is important, therefore, that A.T.C. should be able to employ lateral separation methods to a far greater extent than at present and Decca Navigator chains in Europe and North America. The Spanish chain is under construction, but all the rest are operating. In the North British and East Newfoundland chains are tracking and ranging stations for the Dectra chain over the North Atlantic QUEBEC NOVA SCQTJA
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