In order to analyse quantitative radar observations of bird movements, one needs to know the dimensions of the air space surveyed by the radar. The present study shows how to calibrate the operational beam width and the maximum range of any radar for cross sections for different body sizes of songbirds. The trial used an X-band fan beam ship radar of 25 KW (Furuno Fr-2125) and a captive balloon. Metal spheres of different diameters, fastened to the bottom of the balloon at defined distances, corresponding to the radar cross sections of song birds, were moved in all three dimensions of the air space. Simultaneously to the location by radar, the position of the suspended sphere was measured by theodolites.

Captain Emden of H.M. Coastguard's Dover Strait Operations Centre discusses the problems encountered in setting up the experimental Dover Strait Surveillance Scheme and inaugurating the Information Service. The paper, which was presented at a meeting of the Institute in London on 20 November 1974 with the President, G. E. Beck, in the Chair, describes the service today, the results so far achieved and what it hopes to do in the future. A note on the results of surveillance operation between April 1973 and December 1974 will be found at page 244 of this Journal.

When I presented my address to the Institute last year, I took as its theme ‘The Place of Navigation in Modern Air Transport’. Then I endeavoured to put before you some general thoughts and considerations, which I hoped might be stimulating to the further work of the Institute and its Members in the general field of air navigation.

This year marks the twentieth anniversary of the introduction of Concorde into commercial airline service. The first commercial flights were on 21 January 1976 – British Airways from Heathrow to Bahrain and Air France from Paris to Rio via Dakar. Later in that year commercial flights to Washington/Dulles began on 24 May. Services to New York were delayed until 22 November 1977. The first flight of Concorde was some seven years earlier. The prototype took off out of Toulouse on 2 March 1969 and this was followed by 002 from Filton to Fairford on 9 April. At the time it was anticipated that this was the beginning of an era when supersonic flight would be the normal way to travel long distances. Now, in 1996, Concorde is still the world's only supersonic commercial passenger airliner in airline service. This is an extraordinary achievement. The Boeing SST proved to be too ambitious and the programme was halted in 1971 after the United States Government withdrew support, while the Russian TU 144 was beset with problems. One TU 144 crashed at the Paris Air Show in 1973. The aircraft entered internal airline service in December 1975, flying supersonically between Moscow and Alma-Ata, capital of Kazakhstan, carrying mail and freight, but it did not have the range to operate viable intercontinental passenger serives. Certainly by 1985, if not many years before, the TU 144 was out of service.

Vertical speeds of aircraft are always very slight compared with their horizontal speeds (except in the case of aerobatics) and it is first necessary to study the problem of air collisions in horizontal flight, a problem which, from the point of view of the geometry, is analogous to that of collisions at sea.

The fact that the de Havilland Comet cruises at nearly double the flying speed and nearly double the flight altitude of comparable piston-engined airliners is a measure of the great leap forward in air transport which the introduction of gas-turbine engines has brought about. It also illustrates an inherent feature of jet aircraft, for only at high speed and high altitude do turbo-jet engines, and to a less critical extent turbo-prop engines, operate at their maximum efficiency, expressed in distance flown per gallon of fuel consumed. With reduction of altitude and speed, however, the fuel consumption does not fall off proportionately and efficiency decreases rapidly. For example, even when taxying on the ground the Comet's fuel consumption is about 70 per cent of that at cruising altitude, and when flying at sea level the still-air distance flown on a given quantity of fuel is less than half of that at cruising altitude. In other words you get the best out of a jet aircraft when you are going somewhere fast, and when the length of the flight is sufficient for the aircraft to climb to its optimum cruising altitude and remain there for a considerable proportion of the flight time.

Omega is one of a wide range of navigational aids that have been developed and are in everyday use by ships and aircraft. By contrast, outside the military field as yet there has been no significant application of these aids to mobile land vehicles. The reason has been a mismatch between the perceived accuracy requirements of the potential user, what he is prepared to pay, and what technology could provide.

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.

A realistic runway capacity study for two major airports, namely Frankfurt (EDDF) and Chicago O'Hare (ORD) is presented, assessing the effect of optimal scheduling on the runway capacity and air traffic delays. The maximum position shift (MPS) runway scheduling algorithm, used in the study, was developed by Trivizas at the Massachusetts Institute of Technology (1987).

EDDF is studied in the context of 160 major European airports, with a real traffic sample from 6 July, 1990. ORD is studied in the context of 26 major US airports using a large traffic sample from 1 March, 1989. Secondary airport traffic has been assigned to the geographically nearest major hub and time compression has been used to extrapolate to an artificially denser scenario.

The results show that optimal scheduling can bring about capacity improvements of the order of 20 percent, which in turn reduce delays up to 70 percent. These results are the product of a dynamic traffic management process which has been visually validated by observing animated runway operations and monitor functions.

The study has been conducted with TMSIM, a comprehensive, object-oriented simulation tool that allows one to build an understanding of the structure and functionality of the air traffic control system, by modelling its components, their functionality and interactions, and measuring component and system performance. It features interactive route network editing (using menu/mouse techniques), complete route and airport structure modelling, independent flight and ATC objects, 3-D animation, advanced algorithms for scheduling, routeing, flow management, airspace restructuring (sectorization) and performance (capacity and communications workload) analysis.

Dr. Freiesleben, an Honorary Member of this Institute, discusses the geometry of ellipses and hyperbolae on the sphere. These are the curves which correspond to position lines based on the constant sum or difference of distances from two fixed points. Originally applied to astronomical position lines they now have a wider application to electronic fixing systems of global coverage like Omega.

Britain is often thought of as a maritime nation. The history books certainly support this thesis with their chronicles of explorations for trade routes, of the development of overseas commerce, which became rather absentmindedly an empire, of the growth of a navy to defend these interests. As an island race which aspired to global enterprise, maritime affairs have never been far from central policy considerations as our livelihood began to depend increasingly on overseas trade routes for food, raw materials and export markets. And along the way we developed merchant and fighting marines that were supreme in their day. From this global perspective we have been and will, probably, always be a maritime nation.

D. H. Sadler has pointed out that the method I proposed in my paper (34, 247) can be improved, in his view, by the use of the formula

(1 + f) × distance = D.lat × sec(Co)

where the tabulation of Jean be found in his earlier paper (9, 371).

The possibility of reducing the current vertical separation minima in order to increase traffic capacity on economical flight levels has been discussed mainly at the RGCSP (Review of the General Concept of Separation Panel) meetings of ICAO. A collision risk model based on the mathematical model developed by Reich (1966) has been adopted for evaluation of safety of air traffic systems under consideration. This collision risk approach requires several parameters which should be estimated from empirical data on navigational errors, traffic dynamics, etc.

Multicollinearity and its effect on parameter estimators such as the Kalman filter is analysed using the navigation application as a special example. All position-fix navigation systems suffer loss of accuracy when their navigation landmarks are nearly collinear. Nearly collinear measurement geometry is termed the geometric dilution of position (GDOP). Its presence causes the errors of the position estimates to be highly inflated. In 1970 Hoerl and Kennard developed ridge regression to combat near collinearity when it arises in the predictor matrix of a linear regression model. Since GDOP is mathematically equivalent to a nearly collinear predictor matrix, Kelly suggested using ridge regression techniques in navigation signal processors to reduce the effects of GDOP. The original programme intended to use ridge regression not only to reduce variance inflation but also to reduce bias inflation. Reducing bias inflation is an extension of Hoerl's ridge concept by Kelly. Preliminary results show that ridge regression will reduce the effects of variance inflation caused by GDOP. However, recent results (Kelly) conclude it will not reduce bias inflation as it arises in the navigation problem, GDOP is not a mismatched estimator/model problem. Even with an estimator matched to the model, GDOP may inflate the MSE of the ordinary Kalman filter while the ridge recursive filter chooses a suitable biased estimator that will reduce the MSE. The main goal is obtaining a smaller MSE for the estimator, rather than minimizing the residual sum of squares. This is a different operation than tuning the Kalman filter's dynamic process noise covariance Q, in order to compensate for unmodelled errors. Although ridge regression has not yielded a satisfactory solution to the general GDOP problem, it has provided insight into exactly what causes multicollinearity in navigation signal processors such as the Kalman filter and under what conditions an estimator's performance can be improved.

In this paper, based on an article printed on the back of the March 1973 issue of the Pilot Chart of the North Atlantic Ocean, Mr Fricker analyses three collisions that emphasize the necessity for adhering to the concepts of prudence and safety underlying the Rules of the Road; they are no less essential when navigating by radar in reduced visibility. Terms such as ‘right rudder’, readily understood, have not been altered to conform to English Martime parlance.

There are three main reasons why the rules for preventing collisions at sea need revising:

Rule 21 is unsatisfactory. This is particularly the case in encounters between vessels of widely different speeds and manœuvring capabilities when Rule 19 may require an unreasonable manœuvre from the slower and more ponderous craft and Rule 21 at the same time prohibits manœuvre by the more easily handled craft.

If in an encounter the giving-way vessel does not take action in good time, Rule 21 requires that the other vessel must maintain a collision course until the situation becomes so dangerous that action by one vessel is insufficient to prevent collision. For a rule which is intended to prevent collision this seems hardly credible, but in fact Rule 21 does legislate to maintain a risk situation from a time where disengagement might be comparatively easy to a point where it is almost impossible.

It is often suggested that moderate speed in fog should be a function of the performance of the ship in question, but if Rule 21 is to be observed when vessels sight one another, then it ought to be a function of the performance of the vessel required to give way. This of course may not be known until the sighting.

Because it is unnatural to maintain course and speed into a dangerous situation, Rule 21 is frequently disregarded, particularly by navigators of fast and highly manœuvrable craft.

The Royal Air Force has no operational aircraft fitted with Omega but the author was closely associated with two assessments of the system planned and flown by R.A.F. navigators. Both series of flights used the Marconi Elliott AD 1800 equipment. The first flights were from Boscombe Down in mid-1973; the second series, arranged by the Department of Air Warfare at the R.A.F. College, Cranwell consisted of two flights over the North Pole in September 1976.

Following the initial development of 20-channel, all-in-view Global Navigation Satellite System (GNSS), GPS/GLONASS/Inmarsat-3, receivers at the Institute of Satellite Navigation (ISN), University of Leeds, a modification programme has been undertaken to allow real-time differential corrections to be sent from one 20-channel receiver to another identical receiver using a serial link between them. The differential correction software incorporates the RTCM SC-104 and RTCA DO-217 format developed specifically for GPS and adjusted by the ISN to allow simultaneous GLONASS operation.

After successful laboratory testing, real-time differential GNSS tests were successfully completed in static mode between Aberdeen and Leeds via the SkyFix differential data-link, and in dynamic mode at DTEO Boscombe Down using a C-band data-link between the ground and a receiver on board the DRA BAC 1–11 aircraft. The aims of the tests were, (i) to demonstrate real-time differential GNSS position-fixing, (ii) to establish the accuracy improvements brought about, and (iii) to examine the effects of data-link latency and satellite PDOP on the solution accuracy.