In this lecture the aim is first to establish of position of “airworthiness” in the field of “safety”. To draw a comparison, airworthiness is but one element of a complex jigsaw puzzle in which all the pieces must properly interlock in order to produce a satisfactory safety picture. This parallel applies too in the sense that if the shape of one of the elements is altered, all the adjacent elements must be altered to maintain a perfect fit. Arising from this, it is clear that, if safety and efficiency of air transport are to increase, then airworthiness provisions must be ever more closely linked with the conditions under which the aeroplane operates. The second aim is to draw attention to those airworthiness matters to which the designer could most profitably direct his efforts.