The work of the Greenwich Observatory throughout the three centuries of its existence has been characterized by the painstaking efforts of its eminent directors to attain an ever-increasing degree of precision in pinpointing the positions of the heavenly bodies, with a view to the improvement of the science of navigation. The pursuit of this purpose, in accordance with the express desire of its founder King Charles II, has been assisted by the steady improvement in the accuracy of the instruments with which it has been equipped, and these have naturally also been applied to investigating problems of a purely theoretical nature. Nevertheless, the tradition pioneered by the first Astronomical Observator (or Astronomer Royal) John Flamsteed (1646–1719) whom the King in 1675 charged with rectifying the coordinates and motions of the heavenly bodies, has remained predominantly practical and utilitarian.

Inertial navigation has been in airline use for some five years and a substantial amount of experience has been built up. The system seems to have fulfilled the expectations of operators. In this paper, which was read at a meeting of the Institute in London on 8 January 1974 with the President in the Chair, Mr. Edwards of British Airways discusses its accuracy and the cost of ownership.

In 1969 a paper was presented to this Institute by F. J. Sullings of the then B.O.A.C. which described some of the engineering aspects of INS and predicted in some detail the costs of operating such equipment for a fleet of twelve B747 aircraft. It is the purpose of this paper to refer back to those early predictions and to make comparison with what has actually been realized. Sullings also referred to the anticipated navigational accuracy of the equipment and this paper will demonstrate that the anticipated accuracies have consistently been exceeded since the first use of the equipment by B.O.A.C. in May 1970. Finally, since the equipment has now been in use for five years, it is considered appropriate to review some developments in which airlines are taking an active interest.

This paper was presented at a joint meeting of the Institute with the Institution of Electronic and Radio Engineers in London on 15 January 1975. The theme of the meeting at which six papers were discussed (a selection of which will be published in the Journal) was Advances in Airborne Equipment for Navigation and Freight Control.

Modern data processors because of their increasing power and flexibility are increasingly used for a variety of functions in modern aircraft, both civil and military. It might seem that a flight control system could be designed of the form shown in Fig. 1, with a powerful central processor taking in signals from all the relevant sensors, gyros, pressure sensors, radar, &c., and operating the control surfaces so as to drive the aircraft along any desired course. But such a system would be quite inadequate in two vitally important aspects: there is no facility for inputs from the aircrew and no account has been taken of failure cases. These and other factors drive the control system designer inexorably towards a total system structure very similar to the type currently used in operational aircraft. There are of course a wide variety of such systems, but most of them are characterized by a number of common features.

Position fixing with the Omega hyperbolic navigation system requires the use of charts or tables unless the receiver itself is able to display the geographical coordinates directly. Plotting position lines on Omega charts is a simple operation but owing to their small scale (1 : 2, 187, 400 for the Mediterranean area) it is impossible to obtain a satisfactory accuracy of fix, while the use of Omega tables becomes particularly laborious when frequent fixes are required.

A Device known as the Simplified Astro Platten (S.A.P.) is presently being marketed by the Bucks. Gear and Engineering Co. Ltd., of Middle Lane, Mount Pleasant, Aylesbury. It consists of a large rectangular plastic sheet some 29 in. by 16 in. on which are engraved two graduated semicircles with parallel diameters separated by a space of 2 inches. This sheet, on which pencil lines may be drawn and which can easily be cleaned when the lines are no longer required, is housed in a stiff plastic protective envelope. A mimeographed booklet of instructions includes examples and answers, for practice. There is no indication of the principles on which the device is based but the idea is certainly not new.

In 1974 Dr. David Lewis was awarded the Institute's Gold Medal for his work on indigenous navigation methods in the Pacific, and his many remarkable feats of practical navigation. The following account is of perhaps the most remarkable of his voyages which was an attempt to circumnavigate the Antarctic Continent on his own. The first part of the voyage, which culminated in January 1973, was mentioned in the formal citation for the award; the second part, which is every bit as remarkable, finished in Capetown in March 1974.

No one had ever sailed single-handed through the Southern Ocean to any part of the Antarctic continent, not even by way of Drake Passage from Tierra del Fuego, which involves a crossing of only about 400 miles of open sea. Since the sole practicable Antarctic landfall for a small vessel is the Antarctic Peninsula (formerly Graham Land) below Cape Horn, Australia, some 6000 miles to the west, was a far from ideal starting point. However, this was where I was working so that there was no alternative but to make Sydney the point of departure.

A ship domain may be thought of as the sea around his ship which the navigator would like to keep free, with respect to other ships and fixed objects. In this paper, which was read at an Institute meeting in London on 12 February 1975 with Captain R. Mayboum in the Chair, Mrs. Goodwin describes studies to determine the dimensions of a domain based on radar simulator performance and traffic surveys in the North Sea. She also suggests applications of this domain concept to marine traffic engineering problems and to traffic control schemes.

In recent years there has been an increasing interest in the sea for it is to the world a means of communication, a source of food and a source of minerals.

The writer's previous article on this subject endeavoured to show that two differing plotting philosophies were currently being offered, one in which the predicted future positions of targets were correlated in time, and the other which displayed unrelated areas in which own ship could come into close quarters with target vessels.

It is becoming common for ship's officers and pilots to attend special simulator courses to learn the handling of new ships or the navigation of particular channels. A simulator can be defined as any likeness of an object or objects, thus a simple drawing of a ship's bridge is a form of simulation, as is a function diagram or a small-scale model; full-scale models or ‘mock-ups’ are more advanced types of simulator. However a simulator is more commonly taken to be a more complicated set of full-scale models in combination with small-scale models, which usually have the ability to respond to different manœuvring actions with changes in the instruments or the surroundings.

Following traditional naval tactics when outgunned, Captain Wylie laid a smoke screen in the January issue of the Journal and discussed what ‘imply’, ‘seem to think’ and ‘suggest’. Before my actual assertion becomes entirely lost to view may I repeat that a prediction of C.P.A., based only on radar data acquired in less than about three minutes, may be seriously in error. Precisely displayed, with no indication of the magnitude of the possible error, it can mislead. To say as he does that this danger is 'supposed' is certainly to beg the question, and supports my belief that the possible size of the error in C.P.A. is still not fully appreciated.

If an analysis is made of the speed of a ship using data recorded in log-books the results are extremely disappointing, and do not reflect the accuracies of the instrumentation in use. Even data from a satellite navigator, where the speeds should have an accuracy of better than I per cent, give a I-knot band in recorded speed; in a 20-knot ship this is 5. per cent. Such inaccuracies require explanation.

To begin with one must ask what is meant by ship's speed, and different interpretations come from different people. The navigator is concerned with speed over the ground, while the naval architect or marine engineer is mainly interested in the forward speed of the ship through the water. On the other hand a compiler of ocean current data will require both the speed over the ground and the speed made good through the water, but the latter must take leeway into account. Finally, a weather routing consultant is looking for the actual forward speed the ship can achieve through the water in the prevailing weather conditions. All users of speed data may require other related information, such as the ocean currents and the leeway characteristics of the ship, which can in fact only be compiled from ship speed data. At the present time all these different requirements have to be satisfied by the speeds measured at sea and recorded in the logbooks and their abstracts. Ships' officers compile these records, but by the nature of their work they are biased towards the navigational concept of speed.

The basis of wheelhouse design is comprehended in that wonderful Anglo-Saxon word—sea-man-ship. For the design of a wheelhouse should be such that the three elements in a mariner's work—the sea, the man and the ship are linked together in the most efficient manner. At all times and in all positions in a wheelhouse the mariner should have a clear view of the scene outside and also have as many clues as possible to the direction of the ship's head—so that he may relate the ship's head and the outside situation as easily as possible.

It is generally assumed that the ideal distribution for the lateral or vertical distribution of aircraft on neighbouring tracks is as in Fig. 1, where A and B are the centre lines of the routes or altitudes. Navaids and altimeters seem to be designed with this distribution as the ideal. Where air traffic control is imperfect and there is an appreciable risk that two aircraft without longitudinal separation will be at the same nominal altitude on the same route, then I suggest that neither the distribution of Fig. 1 nor that of Fig. 2 is ideal but that Fig. 3 represents the ideal because it minimizes the risk of collision due to air traffic control failure. This hypothesis has implications for the design of navaids and altimeters and for the specification of vertical and lateral separation procedures.

Investigation into the design and accuracy of old-time instruments is always of interest. The Nocturnal probably used from the sixteenth century onwards for estimating the approximate local time at night is well known; with this primitive instrument the Pole Star was viewed through a central hole in a pair of wooden or brass discs. A pivoted arm turned to coincide with the ‘Guards’ of the Lesser Bear, the local time being deduced from an engraved scale. A seventeenthcentury improvement included an extra scale for determining the time by aligning the pointer with the Great Bear ‘Pointers’.