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Aviation History
1957
1957 - 0092.PDF
92 FLIGHT CIVIL AVIATION . . . COVER FROM COAST TO COAST THE two maps reproduced on this page show the Airport andAirways Surveillance Radar coverage that will span the United States and Canada when the new equipment now on order isinstalled. The growing chain of stations represents the first answer to the tremendous traffic-control problems in which flightson high-density routes are already involved, for they provide the essential information—a clear picture of the position situation—required before any effective control can be established. But if the multiplicity of radars is not to become excessive, the surveil-lance equipment must be of sufficient range and reliability for many years of continuous use, and duplication and field mainten-ance must make each station as infallible as it is possible to achieve. It was around these requirements that the U.S. CivilAeronautics Administration and the Canadian Department of Canada wrote their specifications for surveillance radar equipmentthat would give coast-to-coast coverage. The price of the equipment is high—C.A.A.'s order for 23radar systems is worth $9,000,000 and Canada's order amounts to $5,000,000—but in 18 months' time the United States C.A.A.controllers should have a total of 70 civil and military radar installations available with which they will be able to obtain apicture of all the traffic in all the airspace above 15,000ft, and of aircraft on the denser routes—where coverage is more closelygrouped—at altitudes below that level. Most of the new equipment is to be manufactured by theRaytheon Manufacturing Company, who are starting deliveries of their long-range radar system this summer. The company'sproject engineer, Mr. Bruce J. McCaffrey, in a paper prepared for the Canadian Aeronautical Institute, gave some simple explana-tions of the design of the equipment, and they are worth quoting here. For the best range performance, he says, a 23cm (L-band) wave-length has been selected, and signals are transmitted from the largest practical antenna that could withstand the wind and icethat would be encountered during operations over several years. The reflector is 40ft long by lift high and it is claimed that thebeam-width is "narrower than the 2.5 degrees specified." The Raytheon equipment is of the dual-channel type withtransmitter and receiver portions located adjacent to the antenna in a special hut, but the operator can be positioned up to twomiles away; the second channel is normally kept warmed-up but inactive. The limiting range—giving a 50 per cent probabilityof detection—is 88 miles; almost solid display is obtained from a small target at 65 miles. The manufacturers claim that—because Each radar installation shown on the map of Canada (above) and the U.S. (left) has an area coverage of 725,000 square miles Radars indicated by heavily outlined circles will start service from this summer; light circles indicate future coverage. of basic system design—new units can be combined with those already developed at the dictates of air traffic needs. It is generally well known that "circular polarization" canreduce the susceptibility of a radar to interference by rain or precipitation which will clutter the scope; but perhaps less wellappreciated are the mechanics by which this is achieved. The A.A.S.R. provides linear polarization for normal operation,and circular polarization can be manually selected by the operator. Effective discrimination of circular polarization between rain oraircraft return, states Mr. McCaffrey, is due to the reflection against spherical raindrops of circularly polarized waves ascircularly polarized waves; a right-handed wave becomes left- handed when it is reflected from a symmetrical reflector, just asthe mirror image of a reflected right-handed machine screw appears left-handed. An antenna which originates an outgoing right-handed circularly polarized wave cannot respond to the left-hand wave from the raindrop—and since an aircraft is not a symmetricalreflector, it scrambles the polarization of the wave it reflects, although not so completely that the antenna which originatedthe incident wave cannot respond. Other refinements of the A.A.S.R. are the inclusion of a videomapping generator and "moving target indication." The map, which can be of varying scale, is generated electronically on to theface of the operator's radar scopes, so that the geographical position of the "blip" being followed can then be pin-pointed. Movingtarget indication—inevitably reduced in the jargon of initials to M.T.I.—is a filtering process which cuts out reflections fromstationary objects and reduces the indications of the scope to those that are moving. B.E.A. COMMERCIAL APPOINTMENTS CJEVERAL new appointments resulting from changes in the*** B.E.A. commercial department have been announced by the chief executive, Mr. A. H. Milward. In future the department will be known as the commercialand sales department under its director, Mr. Philip Lawton. He is to be assisted by two general managers, Mr. Clive Adams (incharge of sales) and Mr. J. L. Grumbridge (commercial affairs); and Mr. Adams will also act as deputy to the director. Mr. Grumbridge's former post as B.E.A. sales manager will betaken over by Mr Henry Hill, together with general responsibility for the reservations branch. Mr. G. H. Wharton, now handingover his post as sales manager (North America), to Mr. John ^r011; :,s t0 become passenger sales manager, responsible to Mr.Hill; while Mr. L. R. Dougal will take charge of the London sales district. Mr. H. V. Richards is to remain responsible for B.E.A.'sagency and interline affairs. This Piaggio P.136-L am- phibian will be used in the summer to ferry passengers between Naples and Capri. The type is being assembled for sale in the U.S. by the Royal Aircraft Corporation of Milwaukee.
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