The object of this paper is to present various practical solutions to the problems of inertia navigation in a descriptive rather than a mathematical form. Inertia navigation is an automatic bump of locality, a dead-reckoning device which, starting from a known point, seeks to find position. Other dead-reckoning devices measure speed, which is only relative to the fluid sea or air. Inertia navigation measures accelerations, which are absolute, and hence builds up a measure of speed. The accelerometer is, therefore, a good starting point for our survey.

When I presented my address to the Institute last year, I took as its theme ‘The Place of Navigation in Modern Air Transport’. Then I endeavoured to put before you some general thoughts and considerations, which I hoped might be stimulating to the further work of the Institute and its Members in the general field of air navigation.

When there is relative movement between an observer and a wave source the observed frequency changes by an amount depending on the relative velocity. This is the doppler effect, and it has been realized for a number of years that it might be the means of measuring the speed of an aircraft over the ground, using radio waves transmitted obliquely and received again at the aircraft after being scattered at the surface of the Earth. By 1937 radio techniques had developed so far that letters patent were granted for systems which then appeared to be practical. A number of severe problems remained, however, and not until the close of the war did development programmes to resolve these problems make headway. Since that time equipments have been successfully produced, both here and in the United States of America, and sufficient operational experience has been gained for the value of the process as an aid to navigation to be assessed.

In recent years the problem of preventing collision in the air has become urgent because of increased speeds and traffic densities. Some operators now install what have come to be known, perhaps optimistically, as ‘anti-collision’ lights, and at the meeting of the third Air Navigation Conference of I.C.A.O., it was suggested that one or other of these systems, or some new system, should be adopted internationally. Agreement was not reached at that meeting, and the question was discussed again by the Airworthiness Committee as an ‘exchange of views’ item in July 1958. The present memorandum was prepared mainly for the use of the representative of the United Kingdom at that discussion.

When considering the navigational performance of doppler systems it is not sufficient to examine only the inherent capability of the radar system, since the overall navigational accuracy achieved is a product of the complete ensemble—the doppler, the aircraft, its pilot, the heading reference, instrument transmission linkages, and so on.

During the period prior to the formation of an independent surveying service as part of the Royal Navy, the making of hydrographic surveys was a haphazard affair often dictated by circumstances rather than as part of a well ordered and integrated scheme. Ordinary serving officers of the Navy were encouraged as part of their duties to obtain information relating to depths, sea-marks, time of tides, setting of the currents, &c.; especially when on a foreign station. In home waters, although the same directive applied, the Admiralty authorities also sought to improve the standard of charting by helping, and in some cases commissioning, private individuals to carry out hydrographic surveys of various parts of the coast. The valuable contribution made by these ‘amateurs’ is shown by the number of charts they produced, particularly during the first half of the eighteenth century. Although the printed charts have survived as a tangible record of their labours, little is known of the methods they employed and the difficulties that confronted them. In the case of Lewis Morris, however, the fact that he was an antiquary, literary scholar, philologist and mineralogist and attained greater fame in fields other than surveying, has meant that a considerable amount of his manuscript material has survived.1 From a surveying standpoint this material includes a number of letters and memoranda sent by Morris to the Admiralty and other interested persons, the original manuscript plans of his survey of the Welsh Coast and a rough survey notebook in which he jotted down his observations while out in the field. The latter is probably unique as, for obvious reasons, field notebooks are inevitably destroyed as the finished product emerges. It is thus possible to obtain a well documented and comprehensive picture of the way in which a zealous individual like Morris set about the stupendous task of surveying hundreds of miles of coastline and inshore waters in the interests of safer navigation.

The regulations governing visual avoidance of collision in the air and the carriage of aircraft lights were originally based on marine practice and extended to include the third dimension in aviation. These regulations were established first by the International Convention for Air Navigation and finally by the International Civil Aviation Organization.

Whenever the subject of air traffic control is discussed reference is made to what are described as ‘areas of high traffic density’. This is a misleading expression because the areas referred to are those in which the traffic density is high in relation to the capacity of the air traffic control system, not to the airspace itself. It is probably true to say that there are in fact only three areas where traffic density is high in relation to the volume of airspace. These are the arrival and departure paths at busy aerodromes and the area occupied by a number of aircraft flying in close formation. Elsewhere the traffic density is not such as to create congestion in the air. It is the traffic control system which becomes overloaded, not the airspace. In this paper an attempt is made to isolate some of the factors giving rise to this state of affairs and to discuss ways of achieving a better state of balance between airspace capacity on the one hand and control capacity on the other.

The continuous data (groundspeed and drift angle) given to high accuracy by airborne doppler equipments, could be adapted for handling by automatic computers which, accepting certain other inputs, can be designed to extract a great variety of information. This paper attempts to outline the contribution that such computers could make to long-range civil air navigation.

There are three aspects of collision avoidance in the air which require mathematical investigation:

• (a) discovery and evaluation of the risk;

• (b) the remedial manœuvre;

• (c) the probabilities associated with (a) and (b).

Rear-Admiral Sir Francis Beaufort, K.C.B., F.R.S. died on 17 December 1857. He was Hydrographer of the Navy from May 1829 to January 1855. We, in the Royal Naval Hydrographic Service, regard him as one of the greatest figures in the history of the navigational sciences, and lest you should think that opinion too highly coloured by professional and national pride I will quote a press notice which appeared in a New Orleans newspaper in 1844, fifteen years after Beaufort had assumed office as Hydrographer.

In 1952 the first transpolar flight by a commercial aircraft was carried out. During the six years that have since passed, S.A.S. aircraft have made 1635 flights across the arctic region representing approximately 26,000 flying hours. Our experience in polar navigation has been built up first on a large number of charter flights, then on regular flights on the sub-polar route to Los Angeles, and finally on regular flights across the Arctic Ocean to Japan.

Since the original survey by Powell, the requirement for aircraft over the Atlantic to maintain their flight-planned or recleared track has been established. The following figures covering flights made by Trans-Canada Air Lines between Canada and the U.K. during the period 8 November 1956 to 16 March 1957 are intended to provide evidence as to the accuracy of estimates necessary in recent calculations appearing in the Journal. Indications of the accuracy of navigators' found winds and of mid-Atlantic position lines are included.

Those familiar with the history of navigation aids may, with good reason, be reluctant to look upon any new aid as a panacea, but there appears to be no doubt that doppler will effect a revolutionary improvement in air navigation as we know it today. We have, for the first time, an aid self-contained in the aeroplane, independent of propagation conditions or weather, capable of giving position information anywhere over the globe with an accuracy certainly adequate to join the approach facilities at the destination aerodrome. Some of us not actively engaged in flying the world's routes tend to be influenced in our outlook by the navigation problems and facilities in high-density areas like western Europe, the United States or even the North Atlantic, and we are inclined to forget that this is only a very small part of the world route structure. The intensity of aviation activity in these high-density areas warrants the establishment of a network of radio beacons, ranges, VOR's and space pattern systems like Loran and Decca to bring order into the traffic flow, besides assisting the navigation of individual aeroplanes. When, however, we consider the immense distances flown by aircraft through Africa and India to the Far East and Australia, to South America and across the Pacific, to say nothing of Communist Asia, we begin to realize what a real dearth of navigation facilities there is over the globe.

One method of controlling aircraft is to assign each a given track, the distance between successive tracks being sufficiently great to ensure that the collision risk is very low. Most approaches to the problem of stipulating what this spacing should be, assume that the possible divergences of an aircraft about its preassigned path follow a Gaussian distribution with a standard deviation obtained by considering all the usual sources of navigational error (e.g. compass error and fixing error) together with meteorological errors due to inaccuracies in forecasting.

The R.C.A.F. Meridian Convergency Computer is designed to help the navigator get the best performance out of a precision gyro which can be compensated for Earth rate, such as the N-I, the C-8, the LDG-I and the polar-path. These gyros are characterized by a low drift rate and provision is made for the effects of Earth rotation to be compensated for at the observer's latitude. Any heading set on the gyro will remain on the gyro provided the gyro remains at the same place. The only drift observed will be the random drift of the gyro itself.

Apart from visual avoidance of other aircraft by pilots the only system of preventing air-to-air collisions at present is by means of air traffic control from the ground. With the increased speed of modern aircraft and increased traffic density on long-distance routes there is a tendency to demand further extension and development of air traffic control to solve the collision problem. The object of this paper is to examine the problems and limitations of air traffic control as a method of avoiding collisions between aircraft in cruising flight and how these are likely to be affected by future aircraft developments.

The paper reviews the influence of gaseous absorption and of precipitation of various forms in the atmosphere on the performance of centimetre-wave radar equipment, special reference being made to the phenomena to be expected at a wavelength of 3 cm, in view of the wide use of this wavelength for marine navigational radar. The greatest adverse effect is caused by widespread heavy rain, which leads to serious reductions of detection range, particularly in tropical-equatorial regions. The influence of super-refraction in the atmosphere is also discussed, and it is shown how skip effects may occur at times at certain ranges.

Synthetic training aids in use in the Royal Air Force today range from a sectioned miniature valve used in teaching basic electronics through a wide range of devices of increasing complexity until we reach the Victor Flight Simulator linked with an N.B.S. (Navigation and Bombing System) trainer, which rivals in complexity, and probably surpasses in cost, the famous ERNIE.

For the efficient use of doppler techniques it is necessary that the beam of short radio waves, emitted from the aircraft shall be reflected from the roughness of the surface or from a plane surface at right angles to the incident beam. Over land there are plenty of roughnesses from which the beam is always thrown back, but over smooth sea there would seem to be no surface feature which can reflect the beam. It therefore is of interest to know the effect of surface winds in producing waves and ripples with various slopes and secondly the frequency with which light winds occur in various parts of the world.