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Aviation History
1938
1938 - 0147.PDF
JANUARY 20, 1938. FLIGHT. 53 conditions alluded to by the powers that be as "visibility 3 minus" and described by the familiar code group CjBI. In normal conditions a transport pilot's height and course are largely left to his own discretion, though each is expected to report his position and height at reasonable intervals in order that the control concerned may keep track of the movements of all the machines in its particular area. Croydon, as the only airport which, until a few years ago, handled any considerable amount of air traffic was, very naturally, the first to be provided with one of these imaginary zones. Others have been arranged elsewhere as traffic conditions demanded. A year or so ago, for instance, Gatwick had its own zone bordering the London-Continent airway area, but with at least the temporary cessa- tion of transport operations at this centre, this is now no longer in action. The first "outside" zone to be established was that sur- rounding the Leeds-Bradford aero- drome at Yeadon, and this, in com- mon with other zones since estab- lished, consists of an air space up to 3,000 feet above sea level and covering an area bounded by a circle of five miles radius centred at the aerodrome. So far the only exception to this rule (apart, of course, from the zone at Croydon) has been that recently established at Ronaldsway, Isle of Man, in which the circle has a ten-mile radius. Other zones will, no doubt, be estab- lished from time to time as conditions warrant such arrangements. The present control system has been developed from the very early days at Croydon, and the methods in use there may, tor the purposes of explanation, be treated as those applying everywhere, though local conditions will naturally demand minor modifications. With the idea of standard- ising such methods to a very large extent, a control officers' school W:LS established some time ago in London, and the officers, many of whom are ex-transport or Service pilots, have been sent out first to Croydon or Heston, to gain practical experience, and thence to the various other con- trol airports in different parts of the country. Mr. J. Jeffs, one of the very first control officers to be appointed, has been in charge of this school, and he is now the previously mentioned inspector of air traffic control. In this capacity he will, no doubt, visit the various aerodromes in order to ensure that the system, as it develops, is fully co- ordinated, and is working, so far as possible, quite auto- matically. The Three Channels At Croydon there are three separate two-way radio sets, each working on a different frequency, and one of them designed solely for short-range work with machines which are actually inside the controlled zone. When, in bad weather, a pilot is given permission to enter this zone:— other machines having landed or been told to remain else- where at a certain height—the operator changes to the new frequency so that there is no possibility of misunderstanding. The Croydon operator at the controlled-zone equipment is in very close touch with the control officer in charge and with the look-out man who is stationed on the control- tower balcony. If, therefore, visibility is such that the pilot is forced to approach the airport on a succession of magnetic reciprocal bearings (QDMs), there is very little lag in the transmis- sion of vital information. More recently, in order that this lag shall be reduced even further, telewriter equipment has been installed, enabling — the control officer to see the actual messages and bearings which are being taken down by the oper- Spaciousness, ampleview in essential directions and carefulplanning are the necessities in the de-sign of a traffic control office. That illustratedabove (left) is the room at the new Jersey Air-port. Above and on the right are two viewsinside the control at London's terminal.One shows the D/F Plotting chart and theother the short-range controlled-zone radioequipment, one of the three radio channels.
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