This paper is concerned with the evaluation and enhancement of the mai
ntenance routines of large and complex technical systems. An 'intellig
ent decision support system' approach is suggested as a method for ove
rcoming the difficulties associated with the scale, variability and ch
angeability of such systems. The main features of the proposed intelli
gent maintenance optimization system (IMOS) are identified. A prototyp
e system is then presented and its main mathematical models of mainten
ance are introduced. Some sample test data and the results produced fr
om them are presented. Other aspects discussed include dealing with ce
nsored data, optimization criteria, the development of a maintenance m
odel selection rule base, the recognition of data patterns and models'
robustness. Results of IMOS system validation against expert advice h
ave shown a high measure of consistency.