This paper provides a comprehensive review of the avionics systems in Unmanned Aerial Vehicles (UAVs), focusing on their structure, functionality, and performance. UAVs have become increasingly versatile, with applications in surveillance, commerce, military, and smart electric grid monitoring. The paper aims to assess and critically review the electronics hardware within UAVs, including various algorithms used for data processing, flight control, surveillance, navigation, protection, and communication. It highlights the complex hierarchies and intricate connections between different subsystems, such as control, computing, communication, sensing, and power management. The review covers navigation strategies, path planning, obstacle avoidance, localization, target tracking, and payload integration. It also discusses the use of Single-Board Computers (SBCs) and System on Modules (SoMs) for data processing and communication. The paper emphasizes the importance of understanding these subsystems to enhance UAV reliability and performance, and it concludes with a future project design recommendation.This paper provides a comprehensive review of the avionics systems in Unmanned Aerial Vehicles (UAVs), focusing on their structure, functionality, and performance. UAVs have become increasingly versatile, with applications in surveillance, commerce, military, and smart electric grid monitoring. The paper aims to assess and critically review the electronics hardware within UAVs, including various algorithms used for data processing, flight control, surveillance, navigation, protection, and communication. It highlights the complex hierarchies and intricate connections between different subsystems, such as control, computing, communication, sensing, and power management. The review covers navigation strategies, path planning, obstacle avoidance, localization, target tracking, and payload integration. It also discusses the use of Single-Board Computers (SBCs) and System on Modules (SoMs) for data processing and communication. The paper emphasizes the importance of understanding these subsystems to enhance UAV reliability and performance, and it concludes with a future project design recommendation.