Review of Low-Altitude Route Planning Methods Considering Airspace Environment

The growth of low-altitude flight activities and the expansion of application scenarios place increasing demands on the safety, environmental adaptability, and coordination of multiple aircraft in route planning. Focusing on low-altitude route planning in complex airspace environments, this review systematically summarizes research progress from three perspectives: task evolution, influencing factors, and planning algorithms, so as to inform route design and the specification of operating conditions. According to the expansion of planning objects, the evolution of low-altitude route planning is divided into four stages, i.e., military penetration, civil single-aircraft, multi-aircraft coordination, and infrastructure networking, and the core constraints and optimization objectives of each stage are summarized. Regarding influencing factors, ground environments, airspace management, flight demand, and socio-ecological conditions are examined to summarize their modeling approaches, and their effects are divided intoThe growth of low-altitude flight activities and the expansion of application scenarios place increasing demands on the safety, environmental adaptability, and coordination of multiple aircraft in route planning. Focusing on low-altitude route planning in complex airspace environments, this review systematically summarizes research progress from three perspectives: task evolution, influencing factors, and planning algorithms, so as to inform route design and the specification of operating conditions. According to the expansion of planning objects, the evolution of low-altitude route planning is divided into four stages, i.e., military penetration, civil single-aircraft, multi-aircraft coordination, and infrastructure networking, and the core constraints and optimization objectives of each stage are summarized. Regarding influencing factors, ground environments, airspace management, flight demand, and socio-ecological conditions are examined to summarize their modeling approaches, and their effects are divided into constraints on route eligibility and cost factors affecting scheme comparison. Regarding planning algorithms: ①To improve trajectory feasibility in complex environments, potential-field guidance, adaptive sampling, and kinematic constraints are incorporated to improve path search and segment connection, while integrated planning and tracking and navigation uncertainty modeling bring trajectory execution and collision risk into the planning process. ②To address safety and efficiency under changing weather conditions, terrain and wind-field modeling, icing-risk constraints, and distributionally robust optimization are used to reduce flight costs, identify feasible trajectories, and mitigate delivery delays, respectively. ③To support multiple aircraft sharing airspace, integrated network design and demand modeling, quasi-dynamic traffic assignment, and combined strategic and tactical conflict management extend planning from individual missions to route networks and the allocation of spatial and temporal resources. The re sults indicate that existing planning algorithms have advanced from geometric obstacle avoidance to kinematic adap tation, navigation risk assessment, and network traffic assignment; however, management rules can hardly enter planning models directly, environmental indicators have not yet been converted into tiered route-use standards, and algorithm validation mostly remains at the level of single missions, which restricts the sustainable operation of public route networks. In the future, research on safety margins and operating conditions of heterogeneous aircraft should be conducted, and route adjustment and mission rescheduling under weather forecast uncertainty should be improved to support safe route use; capacity allocation incorporating feedback on trajectory execution deviations and alternative corridor design should also be investigated to balance operational efficiency under normal conditions with recovery capability following disruptions.