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Aviation History
1933
1933 - 0809.PDF
FLIGHT, OCTOBER 19. 1933 AIR TRANSPORT AIR TRAFFIC CONTROL By MAJOR R. H. S. MEALING (Chief Technical Assistant, Directorate of Civil Aviation, Air Ministry) Major Mealing's paper is of considerable importance in that it is in effect the first public announcement of the Zone Control system. It has been found impossible to keep incoming and outgoing aircraft to separate routes when one of the valleys, leading through the Redhill range of hills, south side of Croydon, is closed by low cloud. The Zone scheme, designed to overcome this, is first being tried out on a voluntary basis, and will, if successful, be made compulsory later Lecture (abridged) given on Thursday, October 12, 1933, before the Royal Aeronautical Society, the 566th Lecture delivered before the Society since its foundation on January 12, 1866. -|p\ EFORE one attempts to define the problem, one I-A. must divide the subject into two parts: — |ll C_) (a) The control of traffic in the air ; (b) The control of traffic on the ground. It will be agreed that the control of traffic on the ground is analogous to the control of maritime traffic in the vicinity of harbours. But the control of traffic in the air is not analogous to any other form of transport. There is no other vehicle used in transport which cannot stand still when necessary, and from the incapability of an aeroplane to remain stationary arises the risk of colli sion with another aircraft or with some obstruction on the ground should it be flying so low. The aeroplane suffers from the disadvantage that within the limits of its power to climb, it can fly at any horizontal plane, thereby seriously complicating any system devised to avoid collision. I will show, however, that we. have learnt to make use of the varying heights at which aircraft can fly to simplify the method of control. Control in the air and control on the ground are closely related, as it is a basic rule that priority must always be given to the machine in the air, and a machine on the ground must not be allowed to endanger the machine in flight. Beyond that one must treat control in the air and con trol on the ground as two separate entities. Having regard to the necessity of air transport proving itself, not by speed alone, but always by regularity, there will in the future not be enough room in the air for indis criminate flying in all directions and therefore flying must be confined to routes. By confining aircraft to routes one can establish ground facilities in a better manner, and the more easily control aircraft to avoid collision. Attempts have been made, and more will be made, to in troduce a system of automatically indicating to one air craft the presence, location, and even the bearing of another aircraft ; but I am not convinced that, although it might be made subsidiary to the system of confining aircraft to routes, it can of itself solve the problem. Confining aircraft to routes is going to make it difficult for the private owner to fly as he wishes, but one must consider his requirements only in relation to regular air transport craft to which priority must be given. This proposed method of confining aircraft to routes is not a theory, but is done every day in bad weather on the Croydon-Continental route, and has stood the test of time. My theory is nothing more than an extension of that practice. The problem becomes one of controlling air craft along an airway and then in the vicinity of an aero drome. When aircraft are following an airway it is not difficult to keep them at a safe distance from one another by in structing them to fly at different heights. Even that method can, due to the varying speed of aircraft, reach saturation point, but it will suffice for some time to come. One should now suggest what aids and facilities are re quired to enable aircraft to follow fixed routes. The most necessary is wireless. Another, very necessary for night use, is light beacons. The wireless is mostly of the direction-finding type, excellent so far as it goes, but I cannot believe that it can be as efficient as the radio \V°\ particularlv the visual directive type. We have turned our faces against the aural type, as at the time when a pilot must be mentally alert it must tend to distract him to have a continual series of noises in one ear and then in the other. The visual directive type enables a machine to follow a route, and will lead it very accurately to the aerodrome from a range of up to one hundred miles, but by itself it cannot do more. It is necessary for a pilot to have indi cated to him at frequent intervals where he is along that route. This will be by the use of short range marker radio beacons, each emitting a different signal. Light beacons are used in the same manner, and though I have heard it suggested that they are superfluous, I do not agree. Should any of the radio beacons fail, they can act, at night time, as a useful substitute. Provided aircraft are: (i) Confined to routes ; (ii) are safely spaced along that route, and (iii) fly at different heights, I see no cause for fearing collision. I have so far dealt with the operation of the machine itself, but I have yet to suggest how that control will be exercised. It rather seems that all routes will be divided into sections with a control officer in charge of each. Each control officer will have in front of him an indicator telling him where each machine is and its height along their own section of the route. Where routes cross, as they must somewhere, there arises the necessity for aircraft, on different routes and on points where they cross, to fly at different heights. This method must, however, become complicated if all aircraft of greatly varying speeds follow the same route, therefore by the time we have the mail carrier and fast passenger aircraft flying at 500 m.p.h. and yet are obtain ing useful service for carrying cargo from the old air tramp which might continue to fly at 200 to 300 m.p.h., we must consider either that these two classes fly on different routes or that possibly the fast machines will fly very high. When we do reach such speeds it is going to be more necessary than ever to prevent indiscriminate flying and the natural corollary to indiscriminate flying is the confining of aircraft to routes. The control of traffic on an airway is not going to be so difficult as the control in the vicinity of an aerodrome. It is at an aerodrome that aircraft converge, and for that reason even to-day we have found it necessary to request certain aircraft to wait until other machines have been helped in, in conditions of bad visibility. Croydon is cursed by having the range of hills rising to nearly 1,000 ft. known as the North Downs, which act as a barrier to 50 per cent, of the Continental aircraft. In bad weather the pilot has the choice of flying in or over the clouds above the hills and then has to come down through the clouds over a busy aerodrome, which can be most unpleasant. His alternative is to follow the line of one of the valleys which penetrate this range of hills, and this is done regularly. That method of approach for an incoming machine is all right until an outgoing machine happens to use the same valley at the same time. Aircraft have been known to pass one another in a valley, but that is very dangerous and should not be allowed. The most natural suggestion is to use one valley for incoming machines and another for outgoing machines— in other words, institute one-way traffic. I made the same suggestion many years ago, and only after much consideration did I admit that I was defeated. The reason is that often one valley is closed from a meteorological point of view and the other remains open ; thereby is one's system of one-way traffic defeated. One must permit both incoming and outgoing traffic to 1049
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