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Aviation History
1951
1951 - 0066.PDF
44 FLIGHT INTERNATIONAL NAVIGATION-AIDS Are We on the Right Track ? A Critical Comparison of American and British Methods : The Case for the Decca Navigator System By C. B. BAILEY-WATSON TEN years ago, radio and radar made it possible forour slender defence forces to counter the violation ofEngland in the magnificent and immortal Battle of Britain. As the war progressed, both radio and radar pro- gressed and, to some extent, that progress is still going on. To-day, extraordinary things can be done by telecommuni- cation—rocket missiles can be controlled, guns can be laid, echoes can be received from the moon, television is in thousands of homes—these and countless other dreams of scientists have become reality. And yet now, as the year 1951 begins, there is still dissension about the basic naviga- tional-aid system which shall be internationally adopted for aircraft. Why is this? It is a patently absurd situation in the light of technical practicality. To some extent, it can be ascribed to the enormous possibilities of the field, and the rapidity with which ever-newer developments have followed hard on the heels of their predecessors. But, equally, it can be ascribed to some muddled thinking, and the rather un- savoury machinations which are international politics. Whatever the cause may be, the effect is deplorable from every point of view. It is now commonly recognized that the possibilities of radar dazzled the " planners " to such an extent that no other means of solving the problem was seriously considered in the early days of (P)I.C.A.O. and I.A.T.A. Again, the war- time attitude of neglecting cost and manpower requirements was a trap which engulfed virtually everyone concerned. Furthermore, although initially a British discovery, radar was developed on such an enormous scale by the United States that, coupled with that country's ascendancy in com- mercial aviation and, equally, its overwhelming financial resources, American wishes were thus invested with undue emphasis at the international discussions, and this to the detriment of claims put forward by sponsors of a British navigational aid with exceptional capabilities. In effect, only the two systems, one American and one British, enter the picture. There are many who hold that the American ideas of which should become the international standard have been shown to be unpractical on a variety of counts. There is now some indication that, after years of being passed over and discredited, the system devised and so obstinately developed by the Decca Navigator Company is at last receiving the appreciative attention of at least some sections of the international bodies. It is not necessary to go over all the ground covered by the international discussions. Suffice it to say that the first difficulty was introduced by the I.C.A.O. concept of a stan- dard aid as a single type of equipment, both in terms of ground stations and airborne installations. This, certainly, had the facile merit of ubiquity and simplicity, and was bolstered by the dominant American wish to get V.O.R. (V.H.F. Visual Omni-Range) accepted as the international standard; a quite understandable desire, in view of the decision to install V.O.R. domestically within U.S. borders. To help the matter along, the U.S. authorities generously agreed to supply V.O.R. installations free of charge to the following I.C.A.O. member countries: Britain, 2; France, 2; Italy, 4; Belgium, 1; and Holland, 1. Perhaps it is unmannerly to suggest that this offer is not altogether unconnected with the fact that U.S. airlines are operated through these countries. Whether or not it is ungenerous to take this view, the fact remains that V.O.R. is extremely expensive, and its operational limitations are such that, to obtain anything approaching general coverage, a large num- ber of sets per country is required. It has been established that the accuracy of V.O.R. under reasonably favourable conditions can, by virtue of the accumulation of station errors and instrument errors, plus receiver-station errors, total up to 6 deg. For this reason, the Americans have not planned adjacent airways at less than 15 deg separation, and with ground-station intervals along the busy domestic routes of not more than 100 miles. The cost of V.O.R. is estimated by the Americans to be of the order of £12,000 sterling per ground station, but the estimate by one of the leading British radio and radar manu- facturers is between £25,000 and £30,000. It does not need skill either in arithmetic or economics to calculate what an enormous sum of money would be required to equip this county alone with V.O.R.—over and above the two installations offered free of charge. Another aspect of the situation is that not only is V.O.R. in a sense uni-directional (to cater for incoming and out- going traffic along an air corridor, two sets of equipment are required) but, in addition, it is merely a short-range (100 miles) homing aid; if a position fix is required, then D.M.E. (Distance-Measuring Equipment) also needs to be provided. In this connection, it is relevant to observe that D.M.E.— which is an entirely separate installation—would cost some- thing between £1,500 and £2,000 per aircraft. It is a com- plicated piece of apparatus which has barely reached an operational state in America.t Trials with a British- designed D.M.E. are well advanced. Against this proposal for an expensive and short-range aid system of limited performance, there exists Decca. Furthermore, the latest development of the Decca system— the Flight Log—gives the pilot a continuous pictorial dis- play of his track on a chart. This is a feature which has so overwhelmingly much to commend it that the Americans have been working feverishly to develop a comparable system for V.O.R./D.M.E. A prototype unit has, in fact, been designed; but, of course, it is hamstrung by the limita- tions inherent in the V.O.R./D.M.E. set-up. t The present situation in the United States is that some 300 V.O.R.installations have been commissioned but, so far as is known, only one route has as yet been approved for full V.O.R. operation. Asregards D.M.E., it is intended that full-scale implementation will take place first at all V.O.R. sites, and then at all J.L.S. sites. Equipmenthas been ordered and installation may be complete by the end of 1952.
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