Mr. J. F. Green, in an article on gyro failure (this Journal, 13, 78). draws. attention to a principle that is of direct importance whenever navigators are dependent, for their information, on an equipment which, though normally serviceable, can develop a gross error. His principle is the triplication of instrumentation: the agreement between the two supposed serviceable equipments is a control on the possible malfunctioning of the third.

In polar regions great reliance has to be placed on the directional information provided by a free azimuth gyro. For sufficient reliability the use of three such gyros is advocated. An analysis is made of ‘the best two out of three’ principle—taking into account the fact that in practice no two gyro readings will be identical.

It is demonstrated that for a given reliability attaching to an individual gyro, the reliability of a three-gyro system represents a vast improvement over a single instrument and that there is an optimum way of using the information presented. The advantages of middle signal selection are pointed out and the dangers associated with mean signal selection are explained. Attention is drawn to the extension of this principle to the problems of triple-signal selection in the automatic navigation system of the future.

To obtain all the available information from radar when visibility is poor, it is widely recognized that plotting is essential. No doubt plotting is carried out whenever possible, but in many merchant ships at sea today the ideal has limitations due to manning difficulties. Where the master has only one officer on the bridge to assist him it is not easy to cope with all bridge duties and carry out plotting in the usual way. To obtain full and accurate information a plotting officer must give his undivided attention to make use of the three known elements, range, bearing and own speed in order to produce the other ship's course, speed and nearest approach and follow up with the change of course and speed that may be required to keep out of the region of collision.

The International Regulations for Preventing Collisions at Sea are of the first importance to the navigator; as Marsden puts it, they are ‘the paramount Rules of Navigation’ and it follows that any trouble taken to perfect them is well worth while. They must be comprehensive and clear, simple enough for the sailor yet precise enough for the lawyer. Considering this, the wonder is perhaps that they are as good as they are. Since they are to be discussed at the International Safety of Life at Sea and Load Line Convention this year, the subject of their revision is a topical one and worth the attention of every mariner.

The story of the Regulations is not without interest. They did not, of course, spring fully fledged into being and they are little more than one hundred years old—a very small fraction of the time that man has been navigating the seas.

It is almost two years since Wing Commander Dickie's survey (11, 259) emphasized the importance of improving methods of control so as to allow more movements in a given volume of airspace. Since then, much effort in many countries has been devoted to the problem. The magnitude of these difficulties is not surprising when it is recalled that, in addition to the professional difficulties of flying, navigation and control, various sections of industry are involved, and international agreement must be obtained. At every turn there are political and commercial problems which cannot be ignored by those responsible for initiating action to solve a very difficult practical problem. This note is written in an attempt to examine once again the various possibilities for improving airspace utilization, with the object of discovering some pattern which will lead to progress.

It has been stated that at all times both the controller and the pilot must know the absolute ground position of the aircraft, but it is by no means clear that this really is a requirement. It could well be sufficient to maintain the position of the aircraft relative to the traffic pattern, for this would satisfy the pilot's aim which is to travel in accordance with his flight plan, and also the controller's aim which is to ensure safety while making best use of the available airspace.

This paper discusses the operation of a simple computer which, when used in conjunction with a doppler sensor, will enable automatic navigation to be performed. It is primarily designed for the civil air operator. A series of rhumb lines may be flown and position relative to the desired track and destination will then be displayed. Directional command signals to the pilot and autopilot enable the track to be closely followed.

A short technical description of the computer is given and the expected errors and methods of correction are evaluated. Procedures for turning corners, making diversions, regaining track and flying holding patterns are given, together with the limitations or inaccuracies of the navigational information under these conditions.

F. G. Smith describes (this Journal, 13, 109) a system for determining position from a single observation, probably lasting for a time of the order of a few minutes, of radio transmissions from an artificial Earth satellite. There are in this system two engineering difficulties which I think Dr. Smith has underestimated; these are the frequency stability and the power required. In order to establish these requirements it is necessary to consider in some detail how Dr. Smith's system would work.

The following comments have been received on Mr. E. S. Calvert's paper, published in the last number of the Journal. A further selection of comment, including a note by Captain F. J. Wylie, and possibly a reply by Mr. Calvert, will be published in the next number.

The platform shown in Fig. I is one of a series of miniature platforms developed for inertial guidance and weighs only 28 lb. It is a three-axis, four-gimbal platform permitting complete freedom of manœuvre without gimbal lock. Three miniature integrating gyroscopes are used for stabilizing the gimbal system (Fig. 2) and three miniature pendulous accelerometers provide voltage outputs proportional to accelerations experienced by the platform.

The possibility of obtaining altitude as additional information from an airborne doppler navigation equipment is reviewed, and some of the design problems involved are discussed briefly. These relate to the form of modulation used for transmission, the aerial beam shape and the direction of the aerial beams.

It is concluded that an accuracy of ±5 per cent. ±2 ft. over the range of 10–100 ft. might be possible. The work is in an investigational stage, and no specific design is described.

On page 240 of the April Journal, Wing Commander Dickie pointed out that in traffic control as we know it today, it is ground-speed and not air-speed that really matters. As he says, it is not possible for the pilot to maintain a constant ground-speed and it is for this reason that I suggest the concept whereby individual aircraft maintain constant power which, in the short term, must give constant air-speed. Slight changes in power will maintain a planned traffic pattern on any one route at any one height. Individual speeds will of course be different, and overtaking will have to be arranged by divergencies of track or height.

This equipment was originally designed as a pilot aid to facilitate the use of maps on a route flight. It was used to such an extent that several different models have been developed which fall into the category of automatic navigation equipment. However, even the new concept is still an open-loop navigation device, the loop being closed through the pilot or navigator in the aircraft who reduces the accumulated position errors to zero by direct observations. In the most sophisticated form the roller map equipment is driven automatically according to aircraft ground-speed derived from doppler instrumentation and is equipped with an aural flight programme replay device to draw the pilot's attention to salient features of his flight route.

The title of this contribution is, in itself, misleading. All our navigation is planned and devised by human beings, whatever may be the degree of automaticity inherent in any particular system. The navigation of a space rocket is just as human as that of a Polynesian canoe, despite the absence of a working navigator going along ‘for the ride’. In considering the degree of automaticity desirable for a given navigational task we are really trying to decide how best to deploy the available human effort.