1. A system for developing an engine model comprising: a module for generating a state variable model of an engine, said module receiving a plurality of inputs to an engine representative of a particular flight condition and generating a set of estimated engine parameters representative of said engine model; means for comparing said set of estimated engine parameters to a set of measured engine parameters for generating a set of residuals; and a neural network module for receiving said set of residuals and said engine inputs during a training phase and generating a set of estimated residuals.