Abstract: A computer-implemented method for in-flight assessment of freedom from flutter of an airplane, involving analyzing the airplane structure vibrations based on signals indicated by sensors located on the airplane structure. The computations are performed in real-time based on current measurement data collected from the sensors. For measurement data from individual sensors there are determined mode shapes of vibrations. The relevancy of modes of vibrations is determined by subtracting from the vibrations signal the particular mode of vibrations and calculating the value of decrease in the rest sum of squares.