I Would like to describe an approach which is being made by the Air Registration Board to the Safety of complex systems such as those used in automatic landing, or in supersonic and other advanced aircraft, since I believe that these methods may have a further application in the assessment of aircraft reliability.

Airworthiness Requirements can be considered to be of two kinds. There are empirical requirements based on engineering interpretation of past experience, and there are those which stem from a selected level of safety and which involve consideration of probability of occurrences. This paper is concerned with the second kind since it is relevant to the consideration of reliability.