ALMOST all the long-range civil transport aircraft entering service during the next few years will be equipped with some form of instrument system. It is proposed to describe here some aspects of the* developments which have been embodied in one such system, the Smiths Flight System, and to indicate its scope when applied to the operation of such aircraft.Since the war the operation of a high-performance transport aircraft on congested and competitive routes has become an increasingly complicated process. With the advent of the gas turbine, cruising speeds have doubled, and at the same time there has been a tendency towards higher standards of economy and safety. The development of the air traffic control system has brought about a demand for greater precision in navigation, and in the most congested areas by far the greatest number of flights are conducted under instrument conditions. Meanwhile, aircraft have also become more complex, and the pilots themselves are often expected to monitor the operation of the controls and instrumentation associated with the engines, electrics and pressurization as well as carry out the navigation. This extra work has had to be undertaken without any relaxation of the general vigilance which constitutes good airmanship.Improvements in the accuracy and reliability of the basic flight instruments, and the development of new types of instrument have helped the pilot. Apart from the provision of the basic information on heading, attitude and that derived from the basic quantities of pitot and static pressure, it has now become necessary to display the output of the various radio aids. The Radio Magnetic Indicator has provided an effective display of the relative bearing of two m.f. radio beacons viewed against the reference of a rotating compass card. With its extension to display the relative bearing of a VOR transmitter it is still without equal as a combined display of both absolute and relative bearing.Track guidance has become the foundation of many of the radio systems and is convenient from an air traffic control point of view. The Instrument Landing System is a three dimensional example of such a facility. From the earlier presentation of track deviation on the familiar deviation indicator, a number of flight director instruments have been developed. These are all based on the 'quickening' of the pilot's response to a track deviation signal by computing it with the other parameters: the track to be flown, the aircraft's heading, and its bank angle. The result is then displayed on a suitable indicator, which has eased the pilot's load by 410

Over the past thirty years progress in the technologies associated with navigation has been so rapid as to produce a change in the balance between the art of the navigator and the practice of the technologist. The Royal Institute of Navigation was founded at the beginning of this era and one of its major aims was to provide a forum for discussions between practising navigators, scientists and engineers. Therefore, it seems that a consideration of the technical changes should help the Institute to adapt, much as all our social institutions are adapting, as a result of wider changes brought about by science and technology.

requires that the design features are properly balanced, the interaction between software and hardware being an important factor in achieving a proper balance in design, while the approach adopted must depend on the particular system involved. This interaction is not constant, because the relative costs of hardware and software are continuously changing so that the trade-offs must be reassessed for most new designs.

FORUMVOL. XI around airports between aircraft nominally separated by given amounts, laterally, vertically and longitudinally? If this were done, nominal separation standards could be specified for each area to give a specified safety standard; they might well be found to be quite different from those currently used. Such calculations might show whether the collision risk is less on airways or off airways. Publication of traffic density maps might help pilots avoid volumes of highest traffic density.The magnitude of altitude error makes desirable height control for all automatic pilots, the standardization of altimeters and the investigation whether some other variable than pressure might more accurately be used to provide vertical separation, particularly at great heights.

The paper outlines some of the factors to be considered in the design of any complete airborne automatic navigation and control system. It is pointed out that such a system should lower the work-load on the pilot or navigator as well as contributing to flight safety. Modern engineering techniques have produced a wide range of navigation devices, and their safe and economical use in a complete system involves the consideration of a control loop including the displays and the human navigator. The paper examines this navigation loop in some detail. Some simple and some more complex methods of securing safe operation are suggested.