In the development of instrument systems for the purpose of flight control, traditional designs have consistently failed to solve three particular operational problems:

• (a) The difficulty of transition from instrument to visual flight conditions at the final stages of an instrument approach to land in bad weather.

• (b) The preservation of instrument control when the pilot±s attention is, for any reason, directed away from the appropriate instruments. Preoccupation with other duties, lack of concentration due to fatigue, keeping a look-out for other aircraft, &c, are examples of situations when the maintenance of accurate flight control may be lost.

• (c) The effective monitoring of the accuracy and precision with which an automatic pilot is achieving its selected function. Admittedly this can be achieved by the pilot continuously watching his appropriate primary instruments, but this tends to be extremely monotonous, and to a considerable extent reduces the advantages to be derived from effective automatic control. This particular problem reaches its peak under high altitude, high-speed, conditions of cruise of a jet transport, and in the final stages of an automatic approach, automatic flare, or automatic landing, on any type of aircraft.