Providing safe and on-time flight training is one of the most important activities of a university for educating future pilots. It therefore follows that the unreliability of the aircraft participating in the training program is resulted in delays and may also be the trigger for catastrophe. The main aim of the research was the identification of the main caused of failures. It was assumed that the concept of reliability is understood as the probability of the aircraft to fulfil the functionalities as intended. It is also assumed that the object is reparable. As a part of the research, data from the process of operation of the aircraft used in the Military University of Aviation were investigated. The reliability of two types of helicopters Guimbal Cabri G2 and Robinsson R44 has been subject of studies. In this publication the intensity of damage, unreliability and reliability of the helicopters in question as a function of time have been calculated. On the basis of the operating and maintenance data, it was concluded that the majority of the incidents were caused by technical failures in the cooling system, fuel system, impossibility to start the engine and damage to the clutch. In helicopters, the airframe itself was also characterized by high failure rate, i.e. problems with the landing gear and damage to the outside of the helicopter fuselage.