The possibilities for technical progress in every aspect of aviation during the first half of this century have indeed appeared as a limitless horizon. Increasingly since that period, as we have moved outward toward the technical horizons, the course has become rougher, and we find ourselves in the foothills with a high and formidable range of mountains looming into view before us.

These figurative mountains are representative of the increasing interface deterrent which we are encountering at the edge of the aviation systems’ advancing fronts. These deterrents include socio-environmental and political impacts, economic factors, and the need, in many cases, for redirection and/or equivalent progress in non-aviation technical systems which interface with aviation development. Specific areas are increasing costs for R & D, increased fuel costs, environmental effects of new aircraft and air transport ground systems, changing requirements and demands of the public, increasing liability exposure, increasing regulatory constraints and conflicts, etc.