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Aviation History
1937
1937 - 0145.PDF
JANUARY 21, 1937. Keeping track at Croydon. In the top picture Mr. Emerson marshals the position flags on the chart in the control office. (Centre) '' Position please ! " At work on the D F board at Croydon. Pulham and Lympne are the other two stations used in plotting a "fix." (Lower picture) The short-range controlled-zone D/F set at Croydon. This is used only when communicating with machines coming in during QBI conditions. very largely on their own initiative. With new blood coming in all the time it is ob viously necessary for the system to be more automatic and mistake-proof. Hence my use of the expression "signal box." After this apologia let us return to the control system as it is at present. Described briefly, the country is divided into certain sections, known as Communication Areas, each with its central control. These areas are further reduced to what are known as Controlled Zones surrounding certain busier airports. In conditions of poor visibility no machine may enter these zones without permission from the central control and, permission being difficult -to obtain without radio, this rule virtually prohibits radioless machines—for the safety of all concerned. These bad-weather conditions apply when visibility is less than 1,000 yd. horizontally and less than 1,000ft. vertically, and carry the now well-known code group QBI. In good weather a machine's course and height are left to the pilot's discretion ; in bad weather the central control must have a check on all machines in order to prevent the possibility of collision, and must be par ticularly careful about machines which have been given permission to enter a zone. Safety Zones Ten years ago the Croydon control handled the whole of the airline traffic of this country, and the area system has de veloped quite naturally as more radio stations appeared and as the volume of traffic, and, consequently, of radio messages, increased. The present areas and zones in south-East England are shown in the sketch nap on page 50. In addition, all airport adio stations, apart from those at Gatwick md Croydon, whose zones are defined in ietaiL are now considered as having their >wn prohibited areas, enclosed within a •yhnder with a radius of five miles and a lepth of 2,000ft. In other words, when visibility is poor no machine may, without >ermission, approach within five miles of a ;ey airport unless at more than 2,000ft. Within the last year several short-range iirection-finding or D/F stations have been rected, and their duties are confined to any jecessary communication with machines 'ymg within a certain distance of the air- >ort concerned and to the job of bringing se machines in, if necessary, on con nive radio bearings. For instance, a "tot flying between Jersey and Southamp- °n would, after entering the Portsmouth rea obtain bearings from, and report to. » Portsmouth station until told to com- ramcate with Southampton. A pilot flving °™ Birmingham to Gatwick would deal (j Heston until given permission to enter e Gatwick zone and change over tb the ^wick station's frequency. A.pilot taking r °m Gatwick would normally tune in to
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