No one present can be complacent about the standard of aircraft reliability and his contribution to it. This applies to all concerned, to those responsible for the requirement, those responsible for the specification, all those concerned in the design and manufacture of airframes, engines, equipments and components and finally, the user and his servicing organisation. Significant improvement in reliability will result only from a contribution by everyone involved. It seems that in recent years the attention given to reliability has been out of balance with that given to all the other desired qualities. Those responsible for the requirement must be prepared to sacrifice performance or perhaps time, or variety, or pay more, for a gain in reliability; they must be given some indication of the rate of exchange to help them in this judgment. The designer must have this problem of balance and compromise clearly in mind and must play his part in clarifying the issue. Generally we have striven after the best performance possible and because weapons systems take so long to develop this tendency is probably more pronounced. But if you cast your minds back, systems which were regarded as being designed somewhat conservatively have often, overall, given the best service. Thus my first point is that there must be a conscious compromise between performance and reliability, associated of course with the time-scale and cost of the project. The designer must give equal consideration to reliability and to maintainability (the two go together of course) as to performance and other qualities.