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Aviation History
1946
1946 - 1616.PDF
184 FLIGHT AUGUST 22ND, 1946 Lights for London Airport New Unit Control System to be Installed at Heathrow : Telephone Relays Provide Infinite Flexibility THE unit control system for airfield lighting whichis now ready to be installed at London Airport(Heathrow) was demonstrated last week to senior officials of the Air Ministry and Ministry of Civil Aviation at the New Southgate factory of Standard Telephones and Cables Ltd., where it has been designed and constructed. For the purpose of the demonstration (which was also in the nature of a final official test of the equipment) a "pilot's eye" model of the airport's runways with a complete representation of the approach lights, contact (or flarepath) lights, taxiway, and obstruction lights, was erected so that it was possible simultaneously to observe the functioning of the entire system from the viewpoint of both the air traffic control officer and the pilot of the approaching aircraft. The system was explained and demonstrated by Mr. E. M. S. McWhirter, engineer in charge of remote control at the factory. Two great requirements that had to be borne in mind in planning the system were that it should be completely flexible and capable oi being extended whenever necessary without intertering with the operation of the lighting already installed. Moreover it had to provide in- stant control of the great number of lights and other electrical services spread over an area of some 16 square miles. The first stage of construc- tion of the London Airport requires air- field lighting for three runways, each cap- able of being used in two directions, but when fully developed to nine runways, the airport will consume as much electricity as a fair-sized town. Ac- cordfngly, the power system has been planned on the basis of an 11,000-volt main ring cable fed from an outside supply over two separate routes, and with supply transformer sub-stations strategically placed as near to the load centres as possible. Present requirements are catered for by 12 of these sub-stations through which are fed some 300 lighting circuits and more than 2,000 different fittings, and 555 relay units are distributed among the dozen sub-stations and the control centre. This equipment is arranged so that the addition of new units will permit a further 40 services to be controlled from each sub-station, that is, a total of 480 additional services, and as the airport grows stage by stage from its present three runways to the final nine, extra racks and more sub-stations can be added as necessary. Something Entirely New For such a lighting system the control unit obviously had to be something entirely new. No system existed which would provide the complexity of controls required with the almost instantaneous response and flexibility demanded for an airport, and after some two years' de- velopment work, Standard Telephones and Cables Ltd., QUICK AND EASY : Detachable switch panels on the control desk canbe removed without tools, and connections are plugged in. collaborating with the Air Ministry Works Directorate, has produced the new unit control system which, it quite reasonably claims, will make London airport the best- equipped airport in the world in this important respect. Extensibility The control desk itself is built in units—something like an expanding bookcase—so that new sections to control addi- tional runways can be added without disturbing the exist- ing ones. On the left is the airfield indicator model on which the controller can see at a glance an exact reproduc- tion of the airfield lighting, and in a covered well on the extreme right is a telephone by which any fault disclosed on the mimic can be reported direct to the engineer and rectified at once. On the left of the control panel is the large knurled knob for runway selection. On top is an illuminated aircraft so that error in selection is hardly pos- sible. Wind direction and speed indicators are mounted next to the selector. Below the selector knob is the "pulse key" (of which more later) the in-pulse and out-pulse indicators, check switches, and an emergency black-out button, which we hope will never again be required. The rest of the panel is devoted to some 50 switches for '' setting up '' whatever combination of lights is required— lights which do not come on until the master pulse key is operated. Briefly, this is how the system works. The master pulse key operates a series of telephone relay units, arranged rather like the branches of a tree (the explanatory diagram looked exactly like a genealogical tree) each branch spreading out into three more branches and so capable of infinite extension. The pulse signals go shooting of! down the branches, their actual paths being decided for them by the setting-up switches, and, having lit the various lamps, return to give an " indication back " on the controller's "mimic" air- field. A check key locates any fault that may occur. As every setting-up switch has an illuminated top, these *" flash just like the lamps on a pin table as the relays click their way rapidly through the operation, and the airfield lights spring up in equally rapid rotation. The "tree" layout permits trie whole operation (irrespective of the number of lights involved) to be carried out, and indicated 1 ck, over 12 telephone wires in a ring main cable. Two lighting systems are catered for—the Drem (named after the Scottish airfield where it was first installed) with filament and sodium funnels, lead-in, totem poles, and war- time R.A.F. type flarepath lights; and a later straight- approach type comprising high and low intensity approach lights, and high intensity flarepath (or contact) lights. Other lights, such as glide-path indicators, flood lights,
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