Before embarking upon the business of this paper I should like to make one or two general remarks by way of explanation.

It was suggested by two members of the Council that the present situation with regard to ancillary power services on aircraft was far from satisfactory, and that the question might well form the basis of a lecture before the Society; moreover, that such a lecture might be more interesting and valuable if presented as a joint paper by a member of an engine firm and an aircraft firm respectively. Mr. Nixon and myself have had the honour of being asked to collaborate in this connection and we trust the result will be acceptable to you.

The problem under discussion is one which concerns both aircraft and engine constructors to an equal degree. Yet although their interest in it is a common one, inevitably their viewpoints will be different. This is not to say, however, that their conclusions will clash, and I want to make it clear that in setting out my views, as those of an engine designer, I intend them to be complementary to those of Mr. Chaplin, with the hope that taken together, they will in so me measure help in leading towards a complete solution of the problem.