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Aviation History
1969
1969 - 2460.PDF
mum international, 17 July 1969 AIR NAVIGATION nearly linear system for the last stage of approach, flare and rollout. The geometry also gives good overshoot and take-off guidance which cannot be provided by an in-line angular system. The use of correlation techniques permits the design of systems at microwave frequencies which are compatible with the ICAO ILS transmissions. The hyperbolic geometry can be matched to the normal sensitivity arid rate of change of sensitivity required for aircraft couplers and control systems. The use of localiser transmitters which straddle the runway overcomes all the problems which are inherent in in-line angular systems, and the correlation techniques, which have been successfully applied in military radar and communication systems, provide time and velocity discrimination which enables the effects of interference to' be eliminated. The programme at RAE is primarily concerned with thoroughly evaluating the technique to establish its accuracy, stability, reliability and integrity. Work is sufficiently ahead for RAE to be satisfied that the objectives can be met and it is clear that the applications extend far beyond the automatic landing requirements. The following areas of work involving Gee chain closure WHEN THE SCOTTISH GEE chain closed down earlier this year after 21 years of service to aviation, Mr E. L. T. Barton, lately retired chief of telecommunications NATCS, Board of Trade, performed the closing ceremony at Lowther Hill. He called up the slave stations in turn: Great Dun Fell in Cumberland (2,788ft), Craigowl Hill near Dundee (1,400ft), and Rhu Stafnish in Argyll (709ft) all came on the air to say farewell. The day began with an informal luncheon for a group of men who had been closely associated with Gee since its inception. Gee was the highly accurate navigational system first used by RAF Bomber Command over occupied Europe during the war. The Scottish Gee chain was built immediately after the war to cover the aviation routes from Scotland to the south. It was the only civil chain built, and resulted from co-operation Mr Barton performing the switching-off ceremony with (I to r) Air Marshal Sir Walter Pretty, Mr 0. C. Dovies, Mr C. G. Phillips and Mr R. M. J. McMillan, officer in charge, Scottish Gee chain CPILS illustrate the overall potential: (a) Low cost, high quality guidance for small airports; (b) Application to runways and sites unable to fit a VHF ILS; (c) Military tactical use; (d) VTOL, STOL, and helicopter operations; (e) Missed approach and take-off guidance; curved guidance for noise abatement or obstruction avoidance; (f) Terminal area guidance, monitoring and control. The way in which CPILS works is by using two localiser transmitters and two glide-slope transmitters. The localisers are placed on both sides of the runway midway along its length and the glide-path transmitters on both sides of the runway at opposite ends. The "straddle" pattern thus produced gives a zero DDM along the runway centreline and down the glide-path in the same way as conventional ILS but the radiation pattern is hyperbolic so that the further from the transmitter centreline, the more curved the line. The C-band microwave transmissions are correlated in the aircraft in such a way that position information becomes a function of time difference and not of the relative field strengths. The accuracy of the system is therefore that of the well-proven hyperbolic navigation systems. The increased integrity is derived from a combination of correlation protection and beam tailoring. Protection against reflected signals is derived principally from the correlation process with further suppression occurring from the use of C-band frequencies which allow accurate definition of beam shapes. between industry, the airlines and Government through a committee chaired by Sir Robert Watson Watt. The RAF system first got off the ground on June 26, 1941, and met two distinct requirements. It enabled a navigator, after penetrating deep into enemy-occupied Europe, to get his aircraft back to base or locate a safe alternative before his fuel supply ran out. Coverage was not limited to home territory and targets, particularly in such places as the Ruhr which had previously been so elusive, could be located. Effectiveness of the bombing offensive also improved since accurate navigation on the first stage of the journey improved the chances of locating the target at the far end. Other wartime aids such as G-H, Oboe, Rebecca/Eureka and H2S soon followed but Gee remained for many years the basic aid to navigation for the Mosquitoes, Wellingtons, Lancasters, Halifaxes and Stirlings of Bomber Command. During the 1950s the Scottish Gee chain proved invaluable to BEA on their Scottish services. In recent times civil aviation came to rely on other electronic devices, such as ADF, VOR and radar. The RAF continued to use the Gee system, including the Scottish chain, until this year but because they too are now) turning to other systems the Scottish chain has been closed down. Severe winters Tributes were paid to the men who man the Lowther Hill station. They had a hard time in winter and were often cut off for several days at a time. Arctic conditions are common for seven or eight months of the year, only equalled in Greenland, the Canadian North and the Antarctic. It was pointed out that although they were saying goodbye to Gee this would not be the end of the four stations because over the years they have become the principal radio communications stations of the National Air Traffic Control Service in Scotland. NATCS at Prestwick exercises varying degrees of jurisdiction over all air movements in Scotland and it does so through these stations, which, because of their altitude, cover between them a substantial proportion of Scottish airspace. Now at Lowther Hill the BoT is building, not without great difficulty because of weather conditions, two large radar installations, both housed in huge radomes, to feed back to the Air Traffic Control Centre at Prestwick as a small part of the £200 million modernisation programme of the service.
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