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.