Abstract: A computer system for managing replacement components for equipment having a plurality of components, each component having a limited useful life, has a computer program module defining a duty profile comprising a plurality of usage cases for the equipment, each usage case involving two or more of the components and specified operating conditions for the involved components during execution of the usage cases. A further program module determines a theoretical useful life for each component involved in a duty profile, based on component useful life data under specified operating conditions; and sensors determine and monitor the occurrence of equipment operation corresponding to a usage case and measur actual operating conditions and number of operations. A further program module computes an adjusted theoretical useful life for a component experiencing operations, based on a comparison of actual operating conditions to those assumed for the usage case.