The paper has solved the actual scientific and practical problem of constructing a fuzzy expert system for control and diagnostics of helicopter aircraft engines technical state in flight modes. The algorithm for control and diagnosing of air-craft engines technical state has been further developed on the basis of a modified method of diagnostic matrices and fuzzy logic, which differs from the existing ones in that due to the introduction of fuzzy expert rules corresponding to the physics of processes occurring in aircraft engines with a free turbine, it has made it possible to increase the confidence coefficient decision-making on the presence of a defect in a particular node of the flow path of helicopters aircraft engines at the stage of helicopters flight operation. The implementation of a fuzzy expert system with the use of a Wang-Mendel fuzzy neural network is proposed, which made it possible to determine on a test example the presence of a defect in the compressor, the presence of which indicates a 1 % degree of pressure increase in the compressor.