The four papers printed here were read to a meeting of the Institute held at the Royal Geographical Society on 17 February 1950. They present, each from a detailed experience of particular requirements, an enquiry into one of the major problems of flight operation at the moment. It is clear, both from the papers and from the nature of the problem itself, that no solution can be considered apart from its navigational aspects, and that the whole conception of control is inevitably bound up with the question of position. The problem is therefore of its essence a navigational one.

There has always been, since the very early days of aviation, some form of control exercised over air traffic, an attempt to curtail random activities. The earliest example is perhaps that of the somewhat unfortunate individual who was obliged to stand for long periods in a highly dangerous position at the end of a paraffin flare path. This example shows how soon it was realized that where a collection of individual units are all trying to get to the same place, some of them possibly at the same time, some co-ordination and orderliness must be introduced, and that this could only be achieved by some third party. It was soon seen that certain difficulties prohibited individual countries from making their own decisions on these matters and that, like the high seas, aviation requires a common ‘highway code’. With the ending of the first world war, and the beginnings of international aviation, came the formation of the International Commission for Air Navigation, which had amongst its objects the agreement between contracting states on standardization of rules of the air, and of visual and aural signals. It might well be said that, out of I.C.A.N., air traffic control was born in the period 1919–20.

Before considering in any detail the importance of precise navigation to air traffic control, or attempting to define the word ‘precise’ in this context, it seems desirable to go back to fundamentals and consider certain essential characteristics of a volume of traffic flowing between individual pairs of airports in a system comprising a large number of such airports, randomly distributed and heavily loaded.

The high concentration of aircraft near aerodromes, with consequent collision risk is well known. It is at present necessary, in poor visibility, to guarantee the indispensable commodity of safety by the sacrifice of schedule regularity and fuel economy. So long as this is the case, the problem of terminal navigation and control must be regarded as one still demanding a satisfactory solution.

In daylight and in good visibility no mandatory flying control is either necessary or desirable. The basic task of air traffic control is therefore (a) to give information so as to expedite landings and take-offs in good flying conditions and (b) to give information and instructions in blind flying conditions or at night.

This paper describes a microwave direction finding equipment and gives the results of flight tests carried out to investigate its possible use for air navigation.

The system operates in the 3.2 cm. wavelength band. The aircraft equipment consists of a receiver which sweeps rapidly over a small frequency band, a directional aerial which is scanned in bearing and a cathode ray tube display. The ground beacons are low power c.w. oscillators with an omnidirectional aerial and operate at separate fixed wavelengths to facilitate identification.

The dip of the horizon resulting from the observer's height of eye can be calculated from the formula Dip = 1′·06√H, where H is the height of eye in feet, or by Dip = 1′·93√h, where h is the height in metres. In this paper the latter form will be used so that comparison can be made with studies in international publications.

The term ‘dead reckoning’, so the Admiralty Navigation Manual (1938) says, is a corruption of the old ‘ded-uced reckoning’ or ‘position by account’, and is used to cover all positions that are obtained from ‘the course the ship steers and her speed through the water, and from no other factors.’ (The last italics are ours.) Had Master William Borough, Chief Pilot of the Muscovy Company, and presently to be appointed to Queen Elizabeth's Navy Board, come across this definition, he would have picked a two-fold quarrel with their present Lordships at Whitehall. For his use and explanation of the term is the earliest of which we have knowledge, although it does not appear even then to have been new.

The technical processes of navigation are much the same in all craft, but there are certain requirements and problems which are peculiar to ocean racing. Compared with big ship navigation, the principal differences are:

(1) The ship's speed is irregular and is not always exactly known; it is also much lower so that the tidal streams and other sets play a much more important role.

(2) The course steered is often a constantly varying one, particularly when the vessel is on the wind, or before the wind.

(3) Leeway is a far larger factor.

(4) The violence of the motion and the lack of space greatly increase the difficulty of plotting and calculating.

(5) The methods of fixing the ship are generally less exact and less readily available.

A variety of marine requirements has prompted the Hydrographer of the Navy to design a plotting diagram printed on a transparency which is now under trial in prototype form. British Admiralty chart 5028, as this project is officially called, comprises a thin sheet of flexible and transparent material slightly frosted on one side to take ordinary black lead pencil work. The plotting area is printed on the frosted side and its circular portion has a diameter of 20 inches.

When simultaneous position lines are unobtainable a running fix or transferred position line is generally used. This method depends for its accuracy on the true assessing of course and speed. If, instead of transferring one of two position lines, three are obtainable, only the course need be assessed and used to obtain a position. It is assumed that the speed is constant, or nearly so—a reasonable assumption.