At present the rate of failure of a weather radar set is of the order of 1 failure in 50 sector flights. Probably the most reliable unit of the equipment is the scanner, which is fortunate because it is the most difficult unit to locate in an aircraft by virtue of its size and the need for uninterrupted forward scanning. With its present size the installation of two scanners is not feasible. In a piston-engined aircraft a radar failure when confronted by prolonged turbulent cloud conditions means no loss of aircraft range due to the adoption of optimum turbulence airspeed. The serviceability rate afforded by a single equipment is, therefore, acceptable since speed is not critical to performance. In a jet the inability to pick a way around turbulent cells if the radar fails, necessitates, by the adoption of optimum turbulence airspeed and altitude, a considerable shortening of range. It may be that in a supersonic aircraft, an unserviceable weather radar will make the flight abortive, since the ability to become supersonic will depend on smooth flying conditions.

The main meteorological features of the atmosphere from 50,000 to 70,000 ft. which are likely to be of importance to supersonic aircraft, are the ‘polar-night westerlies’ and the abrupt rises in temperature which take place in late winter in latitudes polewards of 50° or 60°.

The polar-night westerlies blow between 50° and 70° latitude and reach high velocities, increasing with height, from 60,000 ft. during the winter months; towards.the end of the polar night there is often a sudden rise (perhaps as much as 40° C.) at about 85,000 ft., which spreads downwards and is eventually associated with the termination of the polar-night westerlies.

The increase of speed of supersonic aircraft, as well as the decrease of variability of the wind with time at heights above 50,000 ft., have remarkable effects on the punctuality of arrival of aircraft. For instance, on the route from London to New York, the probable error due to wind in arrival time of a 1500-kt. aircraft at 50,000 or 60,000 ft. is about half a minute. This is in contrast with a probable error of ten to fifteen minutes for a 400-kt. aircraft flying at 30,000 ft.

In recent years there have been a number of accidents caused by aircraft flying into high ground. The aircraft were mostly on nonscheduled rather than scheduled flights. This has resulted in much publicity being given to such questions as the licensing of the operators, the sufficiency of the radio or radar carried, and the route-experience of the pilots. These questions are of course relevant, but there is one further question which ought to be investigated and which has received little attention: it is the adequacy or otherwise of the means employed to show relief on charts.

Under present policy the only picture of the relief is on topographical maps (Fig. 1), but it is on charts (Fig. 2) that the route and aids are shown. If the pilot is to check his safety-height in the air, he can do so only by coordinating the maps with the charts. This is cumbersome when he is pressed for time, and generally he does not do it; he flies on the charts using flight altitudes that have been pre-calculated, and the maps remain in the navigation bag unused.

This paper describes an experimental system of representing the reading on an altimeter in the form of a digital code, and controlling the standard I.C.A.O. secondary surveillance radar transponder to give a corresponding pulse pattern.

Different code arrangements are examined and their capacity noted. A possible use of the system in collision avoidance is suggested for use outside areas of close air traffic control. This use would require little additional equipment.

The possibility of completely automatizing the navigation of merchant ships has been the subject of a recent study and prototype anti-collision radar equipment has already been engineered and evaluated. Indications are that, particularly from an economic point of view, there is little likelihood of such equipment going to sea in the foreseeable future, if it is accepted that a principle aim of any such system should be to reduce manning requirements below three watch-keeping deck officers and a captain. The main reason is that complex navigational problems exist at the beginning and end of the voyage and the presence of a trained watch-keeping deck officer offers the most economic solution to these problems. Detailed analysis of these navigational problems shows that the simple application of automatization techniques to existing equipment offers improved, standards of navigational efficiency and thus increased safety and higher productivity. A new radar plotting system, the Decca 969/ARP, is designed to assist a single watch-keeping deck officer to navigate more efficiently by automatizing certain difficult navigational tasks now performed manually.

That the economic need for automatic or semi-automatic navigational equipment and the design of such equipment is a relatively complex matter is illustrated by the recent very full report issued by the U.S. Maritime Administration. It was clear by 1958 that new navigational radar equipment would be required; a design study was therefore commenced.

Many airborne doppler radars in use at present work with several beams in fixed directions and a pair of beams switched in sequence. In this paper, which was presented at the convention held in Dusseldorf in May 1961 (Journal, 14, 480), a new type of doppler radar is described in which a single beam is rotated around the vertical axis with a uniform angular velocity, keeping the depression angle constant. With this type of radar, combined with certain circuits in the transmitter-receiver, the frequency tracker and the data stabilizer, it is possible to measure the velocity of positive as well as negative values (including zero); it also allows easier functioning of data-stabilization. Further, a small and lightweight radar system may be constructed in this manner. This type of doppler radar is considered to be of particular use for small, low-speed aircraft.

The following report, here printed in a slightly abridged form, was prepared under a contract with the U.S. Office of Naval Research and covers the results of research at Key West, Florida, and near Newport, Rhode Island, as well as afloat during the period January 1958 to May 1961. It has so far been unpublished. It describes the results of investigations into the use of high-magnification sextant telescopes and makes recommendations for the improvement of marine sextants and their use. It is here published with a prefatory note and final general comment by Mr. D. H. Sadler, Superintendent of H.M. Nautical Almanac Office.

In the April 1961 number of the Meteorological Magazine, A. F. Crossley discusses Hail in Relation to the Risk of Encounters in Flight. Since it is probable that the Meteorological Magazine does not readily fall into the hands of members of the Institute of Navigation the following brief summary may be of interest, though of course anyone wishing to pursue the subject further should refer to Crossley's original paper and the numerous references therein.

Recent articles in this Journal will have suggested that there is a conflict between certain mathematicians and certain mariners on the subject of the efficacy of the Collision Regulations. The controversy is really philosophic rather than mathematical and, although it would never be suggested that the mathematical system we have seen is anything but flawless in isolation, there are grave doubts that it would work, even on a planet composed solely of deep water and supporting ships staffed only with mathematicians, having collision avoidance as their single preoccupation.

When trials of civil aircraft doppler navigation systems are carried out over land the pattern of results generally show a small along-track error component and a large across-track error component, whereas when the basic doppler radar is assessed, the errors over land are about ±0·2 per cent of distance gone and ±0°.2 in drift (standard deviation). It is not possible to quote system errors for all permutations of doppler equipments and compass systems but it is suggested that a good working figure for the across-track system error component would be about ±3 per cent (standard deviation), i.e. a compass error of ±1°.7. Advantage can be taken of the inherent accuracy of the doppler radar equipment to determine the heading error from a knowledge of track made good and the mean doppler drift along that track.

The standard twin-channel civil doppler navigation computer combines aircraft heading with doppler drift and doppler distance gone to form a ‘computer track’ in coordinates of distance along and across a preset track and distance. The computer is, in effect, meaning the doppler drift between selected points and adding this value to an arbitrary datum (aircraft compass) to form the computer track. If we can determine the true track over the ground we can assume that the error between computer track and actual track is caused entirely by error in the arbitrary datum, i.e. heading error.

The system proposed by Manley (15, 172), to produce true motion on relative displays seems to suffer from two serious disadvantages which were not referred to. The first is that there would be a serious degradation in the resolution of the stored picture, since every time an original echo is rewritten into one of the Tenicon storage tubes the echo size would be increased both in range and bearing by the size of the beam spot. No doubt the full effect of this increase could be reduced by the introduction of pulse shaping circuits between the read-out and write-in points, but nevertheless the original small echo would be considerably increased in size if a number of read-out write-in operations were carried out as would be the case if the information was stored for a sufficiently long time to show true track. As an example, without applying any special pulse shaping techniques a small echo, two spot diameters long and one spot diameter wide, would be increased in size by 65 spot diameters if stored for 30 seconds (i.e. 10 scans of the aerial) and would be increased by 1890 spot diameters if stored for 3 minutes.

The second disadvantage is probably the more serious. Since any signal entering the system remains there until the stored information is cancelled, the effect of interference would be to flood the screen completely in a short space of time.

In the January number of the Journal (15, 104) Captain Wylie discussed the apparent conflict which existed between certain mariners and certain mathematicians about the efficacy of the Collision Regulations at sea. His contribution, which followed the publication in the October 1961 number (14, 379) of Mr. Calvert's ‘Comparison of Two Systems for Avoiding Collision’, was discussed in the same number by a selection of seamen and mathematicians. Followers of this controversy will be interested to read the remarks of Captain Weekes, printed on p. 271 on the subject of how imperfectly many ships' officers understand relative movement. Commander Clissold's suggestion, printed in the same discussion, that Calvert's and Hollingdale's rules should be tested on marine radar simulators is also to the point.

In June 1958 the writer submitted to the Ministry of Aviation a paper, summarized below, on the avoidance of collisions in the air. The views expressed are his own and not necessarily those of the Company for which he works.

1. The rules of the air should recognize that the information available to the pilot, whether obtained by visual or ‘electronic’ means, is likely to be limited by the following:

(a) the pilot's ‘field of view’ is at most ± 90° in azimuth and some ± 20° in elevation relative to his aircraft heading.

(b) a collision course can be recognized, but not the heading, course or speed of the other aircraft.