This paper describes and attempts to assess the viability of the airborne collision-avoidance system based on time-frequency techniques which is proposed, for use within ground-based control systems, by the Air Transport Association of America.

The economic requirement for reductions in horizontal separation standards on high density oceanic routes such as the North Atlantic has motivated the search for a navigation and guidance system combining compatibility with foreseeable separation criteria while at the same time remaining cost effective. In this paper, by the Executive Vice-Chairman of the International Air Navigators' Council, an attempt is made from that point of view, to suggest various systems which are envisaged as meeting the most stringent requirements foreseen. Consideration is given to accuracy requirements, avionic hardware, and optimization of crew responsibilities based on airline experience derived over the past decade. Mr. Waldman is a navigator with Air Canada, but the views expressed are not necessarily those of the Air Canada Management.

1. Introduction. In the spring of 1965, an I.C.A.O. Special North Atlantic Regional Air Navigation Meeting (NAT/ RAN) approved by a margin often to two a reduction in nominal lateral separation from 120 n.m. to 90 n.m. in the ‘principal area’. (The ‘principal area’ of the NAT Region is the area delineated by Gander Oceanic, Lisboa Oceanic, New York Oceanic, Reykjavik, Shanwick Oceanic, and Sondrestrom, South of 700 North.)

At the basic level scientific knowledge has now reached a stage at which sufficient is known to make possible almost any technological achievement in the field of navigation, if sufficient effort can be deployed in its solution. And at the project and engineering level refinements in control and planning have made possible the handling of vast and complex tasks within the necessary disciplines imposed by the available resources.

The rate of growth of air traffic in the London Terminal Area (T.M.A.) is such that the existing airports will be unable to handle it for more than a few years. If a safe and expeditious flow of traffic is to be maintained, even if more airports of the existing type are provided, ways must be found to increase the capacity of individual airports. In any case, it will be necessary to improve the marshalling of traffic between the airports and the air routes to prevent harmful interaction between the various activities. One solution put forward, tacitly assumed that the growth potentials of Heathrow and Gatwick airports were so limited, that a third, and subsequently a fourth, airport of similar design and capacity would be required.

The alternative solution relying on ideas yet to be proved, is more difficult to assess, since possible improvements in technology must be taken into account together with the changes in A.T.C. procedure which their adoption would permit. By 1967, this task had not received the comprehensive study afforded to en-route (Mediator) problems, and no specific operational requirements existed for electronic aids related to this T.M.A. problem.

For this reason, the fairly substantial amount of work which could have a bearing on T.M.A. problems being carried out in various R. & D. establishments and industry could not be directly related to the users' needs.

The last twenty-one years have seen some very striking advances in our knowledge of how animals can determine their location. In many cases we have learned that they have available a wider range of stimuli than ourselves for recognizing landmarks and for pilotage within their home area. Thus the associated senses of smell and taste are extraordinarily well developed in some species. The ability of the males of certain moths to detect the scent emitted by females at very considerable distances had long been known. More recently the extreme sensitivity, and selectivity, of fish to waterborne odours has led to an understanding of how they locate their home waters.

The navigator is frequently faced with the task of finding the course and distance along a rhumb-line between two places on the Earth's surface.

The following paragraphs tell of a two-part investigation into the methods of calculating rhumb-line courses and distances.

Part I deals with a comparison of the methods used and the results are presented in graphic form.

Part II considers the various corrections that may be applied to mean latitude sailing to get better results.

The diagrams in the paper by Y. Namikawa and Y. Yamazaki with the above title (this Journal, 22, 169) are based on a fallacious argument. Since the distance run between bearings is one of the parameters a navigator must choose, it is useless to express the error as a multiple of it. Consequently their final recommendations are also invalid.

Instead, the error should be expressed as a multiple of the shortest distance off, a distance which is not affected by the pattern of observation chosen. The navigator must then choose the angles off the bow, or more correctly off the course made good, to obtain the best fix.

In his original paper, Turner drew attention to the proliferation of units used to measure the same dimension. Granted the decision to adopt a metric system in this country, there could be no question but that SI was the correct one to adopt. It is not precisely the same as the traditional metric system at present in use on the Continent, but it seemed likely that it would become so, and, as the British Standards Institution pointed out, one change from Imperial to SI was far more logical than a change to traditional metric, followed by a change to SI.

SI avoids all the difficulties mentioned by Turner, but, as B.S.I, state (and Turner indeed infers in his statement that ‘speed (will be measured) in kilometres/hour’), we cannot abandon the hour and the day, which SI would require to be expressed as 86·4 kiloseconds and 31·4496 megaseconds respectively. Angle, too, presents a problem. The radian is quite irreplaceable in some mathematical fields but one cannot express a right angle or a complete revolution as a rational figure in radians. Horscroft revives the metric grade of one-hundredth of a right angle, but, as he points out, this logically demands a new basis for time measurement.

A Recent Admiralty Notice to Mariners (No. 1555/1968) advises that a vessel trading the southern North Sea and the English Channel has been fitted with experimental direction indication lights in order to indicate to an approaching vessel the direction in which she is altering course and the duration of the alteration. The positioning of these lights are 10·5 ft. higher than the after masthead light and 4 ft. outboard on each side of the centre line, and they are coloured red to port and green to starboard. When altering course the appropriate light flashes until the vessel is steadied up on her new course.

During the summer of 1968, to celebrate his twenty-first year with the Institute, the Executive Secretary sailed his boat Jester in the third single-handed transatlantic race, from Plymouth to Newport, Rhode Island. Of the 35 starters Jester was the last of the boats which completed the course. He here describes the reasons which led him to take a route which extends the distance of the course from 3000 to 5000 miles, and gives an account of the passage and of some of the problems of single-handed sailing.

Commandant L. Oudet in his contribution ‘Lessons from a Needless Collision’ (Journal, 20, 30) may not have gone so far as to suggest that at no time ought either Tenacious or Placid to have altered course or speed then obtaining. Yet from his account this is plainly the case, a fact for which there must be some technical explanation, although he does not fully disclose it, saying rather, ‘We have not sought to teach but only to stimulate thought among Masters and their shipowners.’ No doubt others are not excluded. His pars. 2 & 3 give the facts in summary and the statement concerning the verdicts of Tenacious that ‘at 1330 she finds the bearing is steady’ plus some muttering about even worse than steady at 1340. This summary he later on amplifies slightly as to the facts:

(1) in par. 16, ‘between 1344 and 1349 … Placid made no (careful) observation.’

(2) in par. 18, ‘Placid did not detect this alteration (by Tenacious at 1340, from 130° to 160°).’

MR. J. A. Lee by his commentary (Journal, 22, 267) rightly suggests that instead of saying in my par. 1 (Journal, 21, 504), as I did after quoting Mr. Carr and Sq. Leader Scott, R.A.F. (Journal, 20, 406, sec. 2, par. 1) my words ‘—and from this deducing velocity and position of the vehicle,’ I could better have simply continued their words, ‘From this acceleration we can then, by successive mathematical integrations, deduce first velocity and secondly the displacement of the vehicle.’ Furthermore, it was superfluous and careless of me to add my quite worthless opinion as to soundness and virtue of expression on their part, but I comfort myself, and I hope also Mr. Lee, with the knowledge that there is no evidence that my opinions have ever previously had any effect whether for good or ill. To the extent, if any, that I can understand Mr. Lee's learned commentary, I believe I quite agree with him and am especially grateful for the clear definition given in his final sentence. If, however, an answer has been given to the question I raised as to the connection of Schuler's 1923 paper with inertial navigation, I am not presently aware of this.

Having followed national and international shipping periodicals of the past years, one can readily observe that a signalling device installed on a vessel giving early and permanent signalling of the ship's course and manœuvre is urgently needed. In this report I will attempt to give brief information on previously known ideas, analyse them, draw conclusions and make a new proposal.

Many readers of the Journal will have learned of the death, at the Hague on the 19 July 1968, of Jacobus Theodor Verstelle. He was aged 68. An authority of international standing on geodesy and hydrography, he was awarded the De Ruyter Medal in 1957 for ‘outstanding services in the fields of navigation and survey’ and became in 1965 an Officer of the Order of Oranje Nassau. He was elected to Fellowship of this Institute in 1955.

Much is being done to ease the burden on the Master approaching ports, and lane separation is the main thing. It would appear that the next logical step would be to penalize Masters who do not conform to the laid down traffic pattern.

It may be argued that the imposition of a penalty will be adding to the danger of a congested port approach, inasmuch as the Master will be worrying about the consequence of a wrong decision; such worrying may tend to cloud judgment.

However all Masters understand the correct ‘port approach’ technique and that therefore all other vessels will comply with such rules. A case for the imposition of a penalty is shown by the marked reluctance of some Masters to follow the lane patterns. I am speaking from experience when I say that I have seen vessels in the approaches to New York, Delaware River and San Francisco where charts show plainly approach and departure routes, deliberately steaming the wrong way in the laid down routes. It would appear that deliberate flaunting of safety features needs penalization of the person responsible, i.e. the Master.

However, before legislation can be enacted for such a penalty, it will be necessary for legislation to be enacted whereby strict conformance to the laws of approach and departure from a port is law, and not, as at present, recommended. While these routes are only recommended some Masters will still ‘corner cut’.

Mr. P. H. Sayers (this Journal, 21, 83) proposes a method of finding the observer's distance from a ship, buoy or lighthouse, the height of which is unknown, by measuring the angle between its waterline and the horizon, the angle thus found being reduced for the dip of the sea horizon for the height of eye. Table 1, an enlargement of the table which the author has used for some 15 years, gives the same information. It requires no correction for dip.

The use of the Sun's shadow is a very old method for position finding. It is easy to adapt a small spirit level to produce a shadow on a millimetre scale which will give results of sufficient accuracy to add to the interest in learning to work out position lines for the Sun; less accurately for the Moon. Schools might find this useful for theoretical and practical classes.

The illustrations explain the principles involved and the constructional details. With practice it is fairly easy to set the style to the height necessary to give a clear shadow and to record its length to one tenth of a millimetre on the scale. To avoid errors of parallax in setting the style, the pinhole sight is held at the required height at the end of the spirit level opposite to the style while the latter's height is measured with the millimetre rule which should be held, vertical, about where the shadow is found to end on the scale.

Schuler himself genially but clearly warned here and there in his 1923 paper that he had not proved his principle, and indicated that the general proof was not within the range of his own limitations, thus inviting his readers to be critical of what amounted to interesting suggestions cheerfully offered. Professor Stratton's commentary (Journal, 21, 507), ‘The Schuler pendulum and inertial navigation’, by its scope, clearness and authenticity, could make effectual the remark that Schuler's calculation of acceleration is not correct except in one and the same great circle and possibly a few other special cases. Schuler jumps to the conclusion that it holds for any spherical motion, thus neglecting much of kinematics. The following standard analysis uses the moving trihedral and the intrinsic equations of ordinary differential geometry. There are many other methods having their own advantages.

In a pungent note published in the October 1966 Journal (Bad Language, Journal, 19, 523), Wing Commander E. W. Anderson drew attention to some of the confusion that had arisen through lack of a precise and accepted navigational terminology. He suggested that if a number of the more contentious terms were defined and accepted by the Institutes of Navigation, the use of ‘bad language’ might die out. It has now been agreed that the British Standards Institution should compile a navigational glossary and to set things going the Institute has formed, under Wing Commander Anderson, a sub-committee to try to sort out some of the terms over which ambiguity has arisen.