While in the design of aircraft hydraulic equipment and landing gear, the final choice of materials used is obviously influenced by a large number of factors including space, wear corrosion resistance, fatigue and, the achievement of minimum weight at an economic cost is usually a primary consideration, the acceptable premium for each kg of weight saved varying from under £5 to over £200 depending on the aircraft type.

The range of materials available to the equipment designer is wide and it is therefore desirable to formulate some guide lines to assist the designer in making the most appropriate material selection for the type of equipment being considered.