Abstract: The invention relates to a method of multiple criteria decision making. In particular, a method of maintaining a complex article is described that includes the steps of; (a) taking a set of options for replacing each of a plurality of components of the complex article, (b) identifying an optimum solution set from the set of possible replacement options of step (a) that best satisfies a plurality of criteria and (c) implementing an optimum solution of the optimum solution set. The step of identifying an optimum solution set comprises the step of evaluating a plurality of potential solutions from the set of possible options defined in step (a) against the plurality of criteria.