A symposium having AIDS as its topic must include descriptions of flight and ground hardware, software programmes, and logistic support. These are dealt with only incidentally in this paper which attempts to examine the role of AIDS in the total management programme of a major aircraft system—the propulsion system. It can be accepted without too much contention that AIDS equipment can now be adequately reliable and provide flight acquired data in virtually any desired form. It is the inventiveness and imagination of prime manufacturers and operators which is being challenged to make the best use of it. The carriage in flight of equipment which does not directly contribute to performance or payload, and can require anything up to its own weight in compensatory fuel, obviously needs careful examination; but knowledge and understanding of the propulsion system characteristics can be priceless in guiding a transport system or weapon system efficiently through its life cycle.