The reliability study of high-altitude unmanned platforms is a very important problem [1, 2]. Platforms of this type are intended to be operational over long periods of time and are widely used in both civilian and military areas. Multi-rotor architecture of such platforms allows for the platform with n rotary-wing engines to stay operational even after k - 1 engines fail. However, failure of a part of the engines causes the increase in load on the others, which results in their reliability deterioration. Moreover, the system’s operational capability depends on the disposition of the failed engines. So, the worst case for this system is the failure of the proximately-located engines. Hence, while developing the reliability evaluation models and finding an optimal architecture of such systems, it is necessary to consider a factor of the “failure dependency”. Thus, the considered systems can be modeled by the k-out-of-n heterogeneous models, which components’ failures depend on the configuration of the failed components. Due to the wide practical application area, a lot of papers were devoted to the study of the k-out-of-n systems. In the talk a review of classic and contemporary papers dedicated to the considered class of systems will be proposed.