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Aviation History
1949
1949 - 0731.PDF
486 FLIGHT AIR RADIO Cole, and a more elaborate system with cathode-ray indica- tion and with remote indication at a number of sites is being manufactured by S.T.C. and Marconi, Instrument Landing System (I.L.S.), the agreed inter- national approach-aid, is a modification of the wartime S.C.S. 51. The "ABAS" (I.L.S.) system of instrument landing has been developed by Pye and will be installed by Marconi. At the moment it is being installed at a num- ber of airfields in the United Kingdom. If the ground installations are well sited, the system gives reasonably accurate and reliable guidance to aircraft. The azimuth transmitter or localizer provides an indication of the air- craft's position laterally with reference to the extended centre-line of the runway, the frequency being in the band 108-112 mc/s. The glide-path transmitter gives the air- craft's altitude relative to a predetermined fixed descent path to point of contact on the runway. The frequency of operation is in the band 320-336 mc/s. Marker beacons, which are low-powered transmitters working on 75 mc/s, are placed along the course and give information as to the exact distance from the touch-down point. There are usually three of these beacons—outer marker, about five miles from the end of the runway; middle marker, 3,500ft, and boundary marker, 250ft. Standard Beam Approach, while still in use in many places, is no longer being manufactured and is being super- seded by the I.L.S. system mentioned above. There is also the blind-approach beacon system known by the war- Position-finding Systems have been developed to enable aircraft and ships to find their positions by radio means, the most widely used of these being the Gee system manufac- tured by Cossor Radar Ltd., the Decca, by the Decca Navigator Co., Ltd., and the Consol, by Marconi. The first two are hyperbolic fixing systems. Gee operating on pulse and Decca on C.W. The ground stations of these three systems have a very high degree of reliability, with automatic changeover from one piece of equipment to another in the event of failures. Cossor Radar also manu- facture a simplified form of Gee known as Gee Track guides. These provide fixed tracks on which aircraft fly to a given destination and should prove valuable where the expense of a full Gee system- is not justified. Development work on a number of projects is being car- ried out in the U.K. to-day. For instance, Ferranti are engaged on distance-measuring equipment (D.M.E.) for use on 1,000 mc/s. The V.H.F. omni-directional beacon (V.O.R.) is being developed under Government contract by Marconi's. This beacon, which is situated on or near the airfield, gives the pilot an accurate bearing indication on his instruments or, alternatively, enables him to home on any radial line he may choose. Speech modulation can be used if required, thus enabling the controller to pass in- structions to the aircraft. The two equipments, D.M.E. and V.O.R., provide the necessary range and bearing information for use in a computer so that any desired track can be flown. Developments in radar include A.C.R. (airfield control radar) and A.S.M.I. (airfield surface movement indicator). (Left) An example of a modern communication by ft coversmilge of 133 to 26 kcls and 95 KC/J to 32 mc/s. (Right) V.H.f-omni-direc- tional range (O.R-8.). This diagram shows the bearing dial and one needle of the crossed-needle indicator for various positions of aircraft on and off course. time code-name of Babs. The aircraft equipment (Rebecca) also has facilities for reception of Eureka beacon signals. Much of the equipment at present in use is a legacy from the war, but mention should be made of the new Murphy high-power Eureka beacon, the frequency range being 214-236 Mc/s and the power output 5 or 1 kW as desired. Ground-controlled Approach (G.C.A.) is at present re- commended as a standby and for monitoring I.L.S. The advantage of this system lies in the fact that it does nojt require any co-operation from the aircraft other than re- sponse to instructions which are given from the ground ; thus the aircraft may be landed in conditions of poor visi- bility provided it has means of communication. At the moment of writing, no British-made G.C.A. equipment is yet available, but S.T.C. will have a complete system ready in the near future. Some details of this are : — Frequency 0080 mc/sPeak power output . 50 kW Maximum range 60,000ftMinimum range.... i^oooft Range accuracy.... ± i.per cent of range from maximum range to 12,000ft. From 12,000ft to 1,000 ft ±r2oft. Elevation accuracy . ±ioft at 4,500ft from the vehicle. Features of this British equipment are its mobility, pan- clirnatic operation and ease of maintenance. A radio link between the vehicle on the airfield and the tower provides remote display, control and monitoring. The equipment has been designed with a view to requiring the minimum of personnel necessary to operate the station. The A.C.R. which is being developed by Cossor provides the controller with a continuous indication of aircraft flying in the vicinity of the airport, whereas A.S.M.I. is used to give a display of movements of ground-based aircraft, vehicles, etc., on the airfield. Its maximum range will be in the region of 6,000 yd, with an accuracy of ± twenty yards. These equipments, together with G.C.A., provide controllers with information on aircraft position in the air or on the ground, although there is still a requirement for identification. ' -•'. Aircraft Equipment Step by step with the increase in complexity of ground installations the aircraft equipment has grown from a single M.F. transmitter/receiver which was considered adequate for pre-war civil airliners to the elaborate installations in use to-day. As a typical example of a modern installation, B.O.A.C. will shortly be putting into service Canadairs and Hermes with the following radio and navigational equipment: — (r) H.F. transmitter/receiver (Marconi AD 107/108) in duplicate. (2) V.H.F. transmitter/receiver (Standard Telephones and Cables STR23). (3) Intercom system (Ultra UL 17). (4) Automatic D/F. (radio compass) (Marconi AD 7092), in duplicate or single twin installation. (5) Rebecca. II (6) Instrument landing system (glide-path and localizer receivers) may be added.
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