A method for managing machine operation comprising sensing a plurality of operational variables for a machine during use thereof so as to generate operational data for said variables. The operational data is processed so as to determine features within the operational data which are indicative of a divergence from a desired operational state of the machine. Confidence values associated with said features are determined and used to assess whether the plurality of features and associated confidence values are indicative of a predetermined diagnosis for said machine. A confidence value for said diagnosis is determined based upon the associated feature confidence values and used to generate a signal indicative of an operational state of the machine. The invention may be used for engine health monitoring applications and may be used for determining necessary servicing or repair work for the engine.