Most civil and military aircraft developed over the past 10 to 15 years have relied upon increasingly complex avionic systems. Some units in this category have been developed to improve the presentation of information to the crew or to decrease their workloads; others have come to play a vital role in automatic flight control (such as fly-by-wire), so that it may not be possible to fly the aircraft without them (and indeed, in the case of ccv the aircraft may even be unstable without them); others again have been developed to give the crew better communication with each other and the outside world, and more detailed information from the radar system and its display. Figure 1 lists a breakdown of systems in a typical modern military aircraft in each of these categories: information and display, control, communications and radar.