AbstractThe purpose of this paper is to develop a framework for the application of proportional hazard modelling to plant maintenance. Two regimes are investigated; a good‐as‐new regime where the hazard rate of the system is refreshed by either failure or preventive maintenance action, and a bad‐as‐old regime where only preventive maintenance action refreshes the hazard rate. The output of the analysis is the recommendation of optimal preventative maintenance plans under both of these regimes. Data for a local firm are used to illustrate the models. The inclusion of proportional hazard modelling is shown to yield improved maintenance plans in both regimes. A proposal for an adaptive scheme is made such that the maintenance plan can be adjusted as changing plant conditions war