Aviation structure failures mostly relate to fatigue damage accumulation and fatigue crack development. Therefore, one of the most important issues in assessing fatigue is development of scientifically based methods for fatigue damage evaluation and structural elements’ lifetime calculation in variable load conditions. These methods make it possible to choose the optimum shape and size of the structure at the design stage and to control the real process of damage accumulation in structures during their operation. In point of structure load-bearing capacity, when a large part of its resource structural material is operated with defects but the operation time is determined by defect development time until its critical dimensions, the methods that make it possible to detect the defects at an early stage and to predict the remaining structures with cracks resources become actual. One of the perspective diagnostic methods that allow dealing with these tasks is the acoustic non-destructive testing method based on the acoustic emission (AE) signal parameter analysis. The practical use of this method is related to the interpretation of the diagnostic measurement data. Protruding problem must be solved by theoretical and practical research of defect origination and development obtained from AE information reading, interpretation and localization, which is recorded in the diagnostic object.