Reliability study of (k-out-of-n)-systems is of interest both from theoretical and practical points of view. There are many investigations devoted to reliability-centric analysis of (k-out-of-n) systems, i.e. systems consising of n components, which are operable while at least k of system components are functioning. Application of such models can be seen in many real-world phenomena, including telecommunication, transmission, transportation, manufacturing, and service applications. A probabilistic study of a real-world k-out-of-n system often helps to develop an optimal strategy for maintaining high system-level reliability. The crucial application in this area is the reliability study of high-altitude unmanned platforms that are intended to be operational over long periods of time and widely used in both civilian and military spheres. 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, that 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 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''. In present paper a reliability function of a heterogeneous (k-out-of-n)-system with independent and dependent components is studied.