Some problems of the electromechanical impedance (EMI), especially its applications for structural health monitoring of aircraft bolt-joints and innovated approach of EMI prediction at loosening of bolt-joints are objectives of research. The full-scale test was performed using the Mi-8 helicopter tail beam. Effect of bolt-joint loosening was investigated by electromechanical impedance (EMI) method. It was shown that loosening of bolt-joint affects significant and stable changes of EMI parameters. It was assumed that both as the weak shift of resonance frequencies or EMI magnitude and resistance change is caused mainly by damping variation. The developed 2D model of constrained PZT based on modal decomposition approach can be used for analysis of influence of the elastic properties and geometrical parameters to properties of constrained piezoelectric transducer. This model has some advantages and can also be useful for structural health monitoring of aircraft components with different possible damages including bolt-joint loosening.