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.

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.

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.

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.

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.

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.

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.