The article is a result of the authors' participation in the European project AISHA II. This project aims at realizing a breakthrough in hte technology of monitoring aircraft health by exploring the capabilities of ultrasonic Lamb waves as the basic sensing principle and by providing an integrated and multidisciplinary research path. The establishment of reliable correlations between parameters of damage and a sensor response during automatic ultrasound NDI is one of the most important conditions for successful creation of the SHM system of aircraft. The results of the theoretical and experimental investigation of this problem are discussed in our presentation