The four papers printed here were read to a meeting of the Institute held at the Royal Geographical Society on 17 February 1950. They present, each from a detailed experience of particular requirements, an enquiry into one of the major problems of flight operation at the moment. It is clear, both from the papers and from the nature of the problem itself, that no solution can be considered apart from its navigational aspects, and that the whole conception of control is inevitably bound up with the question of position. The problem is therefore of its essence a navigational one.