Engine health diagnostic apparatus and method

An engine health diagnostic apparatus 8 is provided for analysing health of a reciprocating internal combustion engine 4. The apparatus 8 comprises feature generation circuitry 90 for processing vibration sensor data 91 received from a vibration sensor 60 detecting vibration at a component of the reciprocating internal combustion engine 4 and generating a feature vector 80 indicating multiple features of the sensor data. Processing circuitry 94 processes the feature vector using a trained classification model which is defined by model parameters characterising a decision boundary 150 of healthy operation learnt from a training set of feature vectors captured during healthy operation of the engine 4. The model generates an engine health indication providing a quantitative indication of deviation of the feature vector from the decision boundary 150 of healthy operation.