Some discussion of the L-1011 analog system will be given before discussing the problems and advantages of digital implementation. It is the most advanced flight control system in operation today and one for which Category III certification was achieved simultaneously with the airframe certification. All L-1011s have been delivered with a full Category III system and all operators are performing automatic landings in service.

Computer techniques have made an increasing contribution to airborne navigation equipment, particularly in the field of radio navigation where in the past computers had generally been too powerful and much too costly to be of practical use. This paper sets out to review some of the progress achieved during the last decade and then to illustrate the impact this has had on airborne radio navigation equipment. In recent years computers have made very significant strides from almost every viewpoint; they have increased in capability and speed of operation, decreased in cost and power consumption, and improved in ruggedness. One characteristic that is particularly relevant to the field of radio navigation is the cost of the minimum practical computer. There is always a limit to how simple a computer can be made before it ceases to be practical and this limit is interesting because it has dropped dramatically over the last decade to a level which makes a computer competitive for solving the simpler problems which were previously solved by other means.

Many papers have dealt with the advantages of using digital techniques and digital hardware in avionic systems. Attention has also been devoted to the special problems of software and the programming of digital computers, although not much of it has been devoted to specifically avionic applications. Very little has been published on the interaction between the hardware and software aspects of the design of avionic systems or on the trade-offs which are possible between the two. This paper deals with various aspects of these trade-offs.

The purpose of this paper is to look at the nature of the advances being made in inertial navigation and in navigation displays. In avionics as a whole the advance from one generation of equipment to another can take different forms; sometimes, notably in flight control and instrumentation, the potential of new technologies is exploited almost immediately to provide more advanced operational facilities and systems become more complex. Alternatively, as in the application of solid state electronics to produce equipment for general aviation, the technology is exploited to reduce weight, volume and costs. Inertial navigation exhibits both trends but to a comparatively small degree; the basic system requirement is simple to define and has changed very little, one of the reasons being the particularly demanding nature of the technology and the very long development time scales involved.

Behavioural science research on seafarers has snowballed throughout the maritime industries of the western world in the last five years or so. The reasons for this may be quite complex, but there is one significant identifiable factor that has given impetus to this research; those countries which are most active in this specialized field extensively employ their own nationals as ships' officers, and increasingly they have had to choose whether or not they wished to continue to do so. Seafaring as a career has few attractions in competition with the wider career opportunities provided by economic growth. That growth has also provided higher standards of education for young people, and consequently a greater awareness of the career choices available to them. The difficulties in recruiting and retaining the able seafarer have become more pressing within each country.

Perhaps the main concern of the Master today should be to foresee the future and adapt himself to it, but that is true for everybody. The gradual change in his position is apparent. Sixty years ago sailing announcements always mentioned the ship's name and her Master's name together, they formed an inseparable unit; today we may look in vain for the Master's name in such announcements. Such outward signs merely illustrate a gradual decline in the Master's position within the overall shipping company hierarchy, though not in the hierarchy on board. It is the result of totally new involvements of shipping management as our society in general becomes more complex and interdependent.

This study of fifteenth-century Arab sailing directions for the Indian Ocean is translated from a paper which was published in the July 1974 issue of Navigation, the Journal of the French Institute of Navigation. The spelling of modern place names has been assimilated to that of the Admiralty Charts and Sailing Directions but other Arabic names and terms have been left in the authors' approximate transliteration. Quotations from the Arabic texts are printed in italics.

Evidence exists which demonstrates that primitive attempts to employ astronomical principles for the purposes of navigation were made by Mediterranean seamen at least a thousand years before the beginning of the Christian Era. But the significant development of nautical astronomy as a science came about at the time when the Atlantic Ocean was being opened up by maritime explorers during the Golden Age of Discoveries, and the lead at the time was taken by the Portuguese under the sponsorship of Prince Henry the Navigator.

It can be said of the oldest form of radio position-fixing for ships and aircraft, by direction finding, that two or more position lines in the form of the bearings of known radio stations provide a ‘common-reference’ fix: within the accuracy limits of the technique, all craft visiting a given spot will get the same bearings, and hence the same fix, at that spot. Similarly, the modern hyperbolic systems Decca, Loran and Omega each provide, within their respective accuracy limits, a common frame of navigational reference for all users. As the term implies, the users can fix position at will within this frame of reference without first having to undertake a calibration or similar procedure at some accurately known position.

The use of hand-held pocket calculators for navigation was discussed at an open meeting of the Technical Committee held in London on 7 May 1975 with the President; G. E. Beck, in the Chair. A number of those who took part in the discussion have prepared written contributions which are printed below with the account of the meeting.

W. D. Rushworth (Directorate of Overseas Surveys, Ministry of Overseas Development): Land surveyors, unlike navigators, do not have to do instant calculations but before we leave an area we have to carry out sufficient computations to ensure there are no blunders in the observations. Overseas in developing countries this usually means a computing session in camp every evening and until a couple of years ago this was a ponderous business, using hand cranked calculators and massive books of eight figure trig. tables. For the surveyor moving on foot these items were often a real burden so that the advent of battery-operated electronic calculators was a godsend, especially once we got calculators with pushbutton trig. functions.

In principle there is of course no difference between the navigation of small and any other kind of craft at sea. In practice, though, the differences seem more apparent than the similarities—differences due to the conditions in which the navigator works and the greater vulnerability of small craft to the elements. I propose to offer some thoughts on three types of small craft navigation which reflect these differences. In terms of sail I concentrate on ocean racing because clearly whatever is effective in that demanding game will also satisfy less urgent requirements. I then refer to single-handed navigation which brings its own problems, and end up with some thoughts on high-speed navigation as exemplified in offshore powerboat racing.

Captain R. K. Emden in his paper in the April 1975 issue of this Journal notes on page 135 that ‘the chief problem’ is ‘to identify by name and port of registry the radar “blip” deemed to be a contravening ship’, and that ‘the problem will be exacerbated as the Service expands’. In the discussion which followed Commander R. B. Richardson mentioned the m.f./d.f. receivers being used to assist ships to keep in lanes, and Captain Lusted mentioned investigations into the use of shore based v.h.f./d.f. for identifying ships.

As one of the perhaps ‘younger personnel’ mentioned by P. R. J. Rawlinson in his note (this Journal, 28, 243) I would like to make a few points. First and foremost, in agreeing with him, I can best quote the Preliminary to the Steering and Sailing Rules of the Rules and Regulations for Preventing Collision at Sea, 1965: ‘In obeying and construing these rules, any action taken should be positive, in ample time, and with due regard to the observance of good seamanship …’