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The paper deals with damage of rotor turbine blades in condition of unstableengine running as engine surging or sudden engine stop. Three aircarft enginesafter the service with a different history were studied. In all cases, an overheatingof the engines accidentally appeared during the service. Representative bladeswere chosen from every engine and studied by light microscopy, scanningelectron microscopy, energy and wave dispersion spectroscopy. The blades wereproduced from JS6K superalloy and coated by Al and Si. This protect layer isranked among diffusion coatings. The limiting factor of the engine operationlifetime is the state of the coatings; therefore, an attempt to correlate the damagelevel of the coating with the service parameters, especially with the overheatingtemperature and the duration of this event, was made. It was found that theexposure to high temperature above the critical value only for several secondssubstantially decreases the engine-power and its durability.