In preparing this lecture I found it necessary, when considering recent changes in aircraft design, constantly to ask myself the question “Is this particular change due to airworthiness requirements or does it arise from reasons other than airworthiness?” In fact, one must consider whether requirements have any influence at all on the development of trends in design. Should design be likened to a runaway horse with requirements following some way behind, or are requirements a strict rein by which the pace and direction of design is controlled?

My own answer to these questions is that the pace at which development takes place is not influenced at all by airworthiness requirements, but that requirements help to prevent design from running off the path of safety. To carry the analogy a little farther, the faster the development is, the more difficult it is to keep it running on the path of safety.