In this paper, which was presented at a symposium on electronic aids to air navigation held in Paris in November 1977 (and subsequently published in the Journal of the French Institute of Navigation), the authors first analyse in detail the mental processes of an aircraft pilot and the ergonomic factors that should underlie the design of any flight data display. They then describe a cathode-ray tube display designed for use in civil transport aircraft and the modifications they found desirable in the light of simulator trials.