New ideas of a really fundamental character are always received with horror and alarm by the general public, and are vigorously repudiated. When Fred Hoyle, in a brilliant series of broadcasts, remarked that his physico-mathematical calculations indicated that newly created hydrogen was being continuously injected into the Universe, the B.B.C. had to take hasty countermeasures. A well-known authoress of detective stories and religious pl ys, followed by a respected professor of science, declared on the air that the earlier t lks had been merely speculative. A similar role was filled in 1543 by the theologian Andreas Osiander, who added a Preface to Copernicus's startling book De Revolutionibus Orbium Coelestium (the author having just died), to the effect that he had only intended as a mathematical hypothesis, not as a matter of fact, to picture a rotating globe revolving round the Sun. From the point of view of pure geometry it was, it is true, merely a matter of a change of coordinates. People settled back comfortably for another sixty or seventy years, until Galileo made certain awkward observations with his new telescope.

Vertical speeds of aircraft are always very slight compared with their horizontal speeds (except in the case of aerobatics) and it is first necessary to study the problem of air collisions in horizontal flight, a problem which, from the point of view of the geometry, is analogous to that of collisions at sea.

The Ministry of Transport and Civil Aviation makes extensive use of radar for the protection of aircraft en route and also in helping to bring them in on approach for a final visual landing. Since we really became interested in radar we have trained 470 PPI directors and 150 precision controllers; the latter use special equipment and cathode-ray tubes which accurately show the glidepath being followed.

Contours of constant probability density have been calculated for Loran systems in different service areas, and from these some ‘Loran navigational charts’, which indicate to the navigator the best two pairs of stations to select, are drawn up. The constant probability density contours are shown in Figs 1–6 (a) and the Loran navigational charts are given in Figs 1–6 (b). The areas covered are: Fig. 1. Japan and the adjacent seas; Fig. 2. NW. Pacific; Fig. 3. Hawaii; Fig. 4. N. Pacific; Fig. 5. NW. Atlantic; Fig. 6. N. Atlantic.

Statistics reveal that the vast majority of mid-air collisions in the past years have occurred during daytime under visual meteorological conditions in the vicinity of airports and at low altitudes. From the description of possible proximity warning or collision avoidance systems it follows that it is just this type of collision that causes technically the greatest difficulties for an operationally and economically feasible solution because of the multiple intruder problem, mutual interference, ground echoes, curved flight paths, and changes in aircraft attitude with resulting changes in aircraft speed. Under these conditions, the automatic pilot, the general introduction of which (for transport aircraft) has been recommended in the interest of collision avoidance, would be only of minor importance as it is common practice to switch off the automatic pilot whilst flying in the aerodrome traffic pattern.

Some readers of the January issue of the Journal may have noticed rather strongly discrepant statements on the subject of self-contained detection devices in the several papers on collision avoidance. For example, on page 43 Gaudillère suggests either constant bearing or constant closing speed as an indicator of impending collision between aircraft; and on pages 82–87 Whitfield and Cade suggest that ships may determine transverse velocity (and hence may identify a collision course) by using a differentiated doppler radar return. But on pages 25–26 the author of this note states that the derivatives of range and azimuth required for this use are in fact too small for successful physical measurement.

Many of the problems arising out of the use of radar in poor visibility can be laid at the door of ‘incorrect appreciation’ of the information available on the PPI, coupled with the lack of timely action to avoid, if possible, a close-quarter situation. To this must be added the over-confident ship handler who has never yet been faced with a collision situation in poor visibility and who may be complacent until too late.

In relative plotting the movement of the observer's ship is ignored. The first bearing B1 and distance a1 are laid off from a chosen origin and after a determined time-interval the second bearing B2 and distance a2 are plotted from the same point. By connecting these two points the relative course of the observed ship is obtained, which enables the observer to tell whether the other ship will cross ahead or astern, what her distance off will be, and when the intersection will occur.

The purpose of this note is to indicate how the design of radar simulators can be adapted to meet the requirements of navigational radar uses. The simulator can be roughly divided into four sections:

1. (1) Control Units, which determine the initial parameters of the target and afford a means of adjusting the rate of change of these parameters.

2. (2) Computers, which determine the range, bearing and elevation of the target from the base.

3. (3) Pulse production and video shaping circuits.

4. (4) Aerial rotation simulation.

The post-war development of air transport has temporarily out-paced the ability of the air traffic control service to provide for safe conduct which is always expeditious, and it has certainly out-moded the concept of visual avoidance. To alleviate the situation in the areas of high-density traffic in the United States, the Air Transport Association of America outlined a requirement for an airborne collision warning device.

Errors in the derived aspect, in course and speed of another vessel, or in the nearest approach, found by plotting radar ranges and bearings on a relative plot can arise in a number of ways, such as errors:

(1) in the bearing as read from the PPI

(2) in range as read from the PPI

(3) in plotting the points on the plotting sheet

(4) in estimating own vessel's course and distance run during the plotting interval

(5) in timing the plotting interval

(6) ‘blunders’.

Dectra is a long-range radio navigation system designed to give accurate position fixing coverage over specific areas, and in particular over long trans-oceanic crossings. The position of an aircraft or ship equipped with a Dectra receiver is continuously available in the form of dial indications relating to coordinates of a Dectra lattice, and in addition this information can be presented pictorially on a normal Decca flight log. The system is at present functioning over the North Atlantic, and flight trials have been in progress since May 1957. This paper discusses the experience gained and the results obtained in the trials.

When I heard about the idea to sail a replica of the Pilgrim Fathers' Mayflower from England to America, I liked the notion. It was not my idea and I had nothing to do with the promotion. What I did was to volunteer to find a British crew and sail the ship, when she was ready—to get her across the Western Ocean, the way the original ship had gone over three and a half centuries ago. I have listened to a good many pessimists who have alleged that sailormen were dead and gone in Britain today, who declared mournfully that nobody could be found to sail ocean-going square-rigged ships in this country, and averred that, in any event, no one could possibly have the least idea how to handle a museum-piece come to life, and so on and so forth, ad nauseam.

Even in good weather, visual collision avoidance by pilots is unsatisfactory for reasons which include the following:

1. (i) When on a collision course the other aircraft has no relative motion across the windscreen and is indistinguishable from other marks on the windscreen until danger is very close.

2. (ii) There is a tendency to focus the eyes on nearby objects on the windscreen instead of at infinity, especially in the absence of conspicuous cloud and at high altitude. This can cause ‘empty field myopia’ whereby a normal pilot becomes nearsighted, his eyes focusing on a location less than six feet away.

3. (iii) In modern jet fighter aircraft the pilot must give much of his visual attention to instruments in the cockpit, such as the altimeter, owing to the difficulty of maintaining longitudinal stability, especially when heavily loaded. In clear air above 35,000 ft, it is estimated the pilot flies half contact and half on instruments.

If you want to ride up a hill on a bicycle you zig-zag up it, because although you travel a longer distance you go much faster and get to the top quicker. There is some similarity between what the cyclist does and what you are trying to achieve when you are planning for a long ocean race. Your object is to find the fastest way from the start to the finish, and whether this is also the shortest way depends on a number of imponderables such as the weather you can expect, the ocean currents, and so on. On a long race, generally the shortest way is not the quickest. What you are interested in is time, and like the cyclist, in distance only so far as it affects time. What you have got to do is to use all the elements that make you go fast, and these include not only winds and currents, but also factors such as the sailing qualities of your boat in different conditions. In addition of course you have to consider how you will stand relative to the others, not only if what you expect happens, but also if it doesn't. In other words your strategy will be tempered by some estimate of the reliability of the predictions of wind directions and currents you are working on. Your overall plan, then, is likely to be partly geographical, which is concerned with finding the least-time route; and partly strategic, which is concerned with not getting caught out.

For anti-collision purposes, the identification of an aircraft requires perception of its presence, detection of its track, and determination of its relative altitude. This evaluation will be recorded by the cerebral cortex and give rise to decisions regarding the action to be taken, which will vary from one individual to another. The avoidance manœuvre will be dictated by the situation and the rules of avoidance, and will involve a psychomotor coordination. Time is the essential factor in the chain of events, since the speed of the pilot's reactions will reduce the possibility of collision.