1. A method of detecting anomalies in an aeroengine, the method comprising: defining a reference behavior model and a current behavior model for a controller of the aeroengine by using time regression that models a behavior of the controller as a function of a data set relating to the controller and including measurements of past behaviors, and state and command measurements of the controller; continuously recalculating the current behavior model for each new data set; and detecting a behavior anomaly of the controller representing an operating anomaly of the engine by monitoring statistical variation between the current behavior model and the reference behavior model, wherein the reference behavior model is defined for each flight regime using an initial data set relating to the controller, wherein the current behavior model is defined for a current flight regime using a current data set, wherein each of the reference behavior model and the current behavior model is a rational filter, the reference rational filter and the current rational filter being defined using a plurality of mathematical formulae, and each formula expressing an output vector at a present instant y(t) representing a current behavior of the controller as a function of output vectors at preceding instants y(t−i) representing earlier behavior measurements, and as a function of input vectors comprising an input vector at a present instant x(t) and input vectors at preceding instants x(t−i), each input vector x being constructed by concatenating the command and state measurements of the controller, wherein each mathematical formula of the plurality of mathematical formulae corresponds to a linear equation between output vectors y and the input vectors x described analytically in the time domain by: 
 A ( q ) y=B ( q ) x with A(q) being a real polynomial having a form: 
 A ( q )=1 +a 1 q −1 +a 2 q −2 +. .. +a ra q −ra and B(q) being a real polynomial in which each coefficient is a line vector having a same dimension as the input vector x and having a form: 
 B ( q )= b 0 +b 1 q −1 +b 2 q −2 +. .. +b rb q −rb with 
 q −1 ( x ( t ))= x ( t− 1), and wherein the detecting the behavior anomaly includes extracting current zeroes and poles from the polynomials associated with the current rational filter corresponding to the current flight regime, extracting reference zeroes and poles from the polynomials associated with the reference rational filter corresponding to the current flight regime, and determining current normality indicators for the current flight regime from the current zeros and poles, determining reference normality indicators for the current flight regime from the reference zeros and poles, and determining the behavior anomaly of the controller when a distance between the current normality indicators and the reference normality indicators is greater than a predetermined value.