Reliability modeling of phased mission UAV systems subject to probabilistic competing failures and dynamic communication dependence

Unmanned Aerial Vehicles (UAVs) serve a vital function in mission-critical operations such as post-disaster emergency response. Ensuring their reliability within dynamic Phased Mission Systems (PMSs) presents significant challenges due to the failure competition in a probabilistic manner arising from the temporal variation of local failures (LFs) and propagated Failures with Global Effects (PFGEs). In UAV-based PMSs, mission tasks are segmented into consecutive, non-overlapping phases, each characterized by distinct system configurations and component behaviors, which introduces statistical dependence across phases. Current reliability models for UAV-based PMSs often assume static relay-based communication between dependent UAVs and the ground base station throughout all mission phases. This assumption neglects the dynamic nature of UAV communication, where UAVs may switch between direct and relay-based modes depending on their relative distance from the ground station. To overcome this limitation, the work proposes a combinatorial reliability methodology that captures probabilistic failure competitions while incorporating communication mode switching driven by UAV mobility. The proposed methodology accommodates various failure distribution types and is validated through a detailed case study of a post-disaster UAV mission. Its accuracy is further confirmed via Monte Carlo simulations.