<p>With the rapid advancements in Internet of Things, high-altitude platforms (HAPs) are revolutionizing various sectors, particularly in the realm of communication networks. As HAPs continue to exert their transformative influence across multiple domains, the aspect of reliability assumes a pivotal role in determining their triumph and widespread acceptance. The proposed study presents a comprehensive reliability analysis of HAPs using stochastic modeling. The investigation focuses on two distinct types of failures affecting a HAP: local failure (LF) and propagation failure (PF). To assess the reliability of the system employing a redundant HAP in the presence of these two failure types, a stochastic model has been developed. Considering the non-Markovian nature of the PF, the proposed model incorporates Markov and semi-Markov processes. Through extensive numerical examples, the presented study explores the influence of failure propagation probability on system reliability and throughput. This analysis provides insights into how the system’s reliability and overall performance are affected by the likelihood of failure. Furthermore, the study offers a comparative analysis of the results obtained from the Markov and semi-Markov models which provides a deeper understanding of the strengths and limitations of each modeling approach, enabling them to make more informed decisions in practice.</p>