I accepted, with some alacrity, your Council's invitation to present this lecture since it reflected a growing awareness of the need to pay particular and urgent attention to the correct use of the human operator in the design of aircraft and their systems. My experience suggests we have paid only lip service to human factor requirements and have relied on the adaptability of aircrews to sort things out once the aircraft enters service. We are also faced with the paradox that, the cleverer we become at inventing black boxes to usurp man, the more important it becomes to define the role, the response, the performance and the limitations of man. Any human factor assumptions we make in the early conceptual stages will critically affect the course of the development. If these assumptions are poorly based we shall finish up with an aircraft of limited effectiveness and the exciting new developments in avionics, now being offered will be substantially wasted.