The first three papers of this all-day symposium, held on 20th November 1969, were published in the March issue of the JOURNAL. The final papers and the discussion are printed below.It can be said that the main cause of premature failure or malfunction of any engineering component is attributable to the design being below the standard required for the environment in which it had to exist. This idea is neither surprising nor new, and applies throughout the whole field of engineering, especially in the aircraft industry which is extremely conscious of the need to design and develop its systems to suit the environmental conditions of flight.In the air-breathing engine industry this need has been recognised almost from the inception of flight. For the successful development of an aero engine there is, therefore, the need to use all the resources of past flight experience to provide initial design information for the engine and its components, and then to test the engine or components to determine that the requirements have been fulfilled.