Method and apparatus for in-situ detection and isolation of aircraft engine faults

A method for performing a fault estimation based on residuals of detected signals includes: determining an operating regime based on a plurality of parameters; extracting predetermined noise standard deviations of the residuals corresponding to said operating regime and scaling the residuals; calculating a magnitude of a measurement vector of the scaled residuals and comparing the magnitude to a decision threshold value; extracting a mean direction and a fault level mapping for each of a plurality of fault types, based on the operating regime; calculating a projection of the measurement vector onto the mean direction of each of the plurality of fault types; determining a fault type based on which projection is maximum; and mapping the projection to a continuous-valued fault level using a lookup table.