3D flight path planning based on RRTs for RNP requirements

Path planning for aircrafts with both military and commercial applications is a complex problem that has gained much attention. Although many research have been presented to solve the problems, path planning that involve aircraft kinematic constraints still present computational challenges. Required Navigation Performance (RNP) is an important factor to ensure the safety of aircrafts for commercial applications. With these considerations, this paper presents an integrated path planner based on modified RRTs (Rapid Exploring Random Trees). It can rapidly generate a new 3D collision-free path in flight taking into account RNP requirements, the aircraft kinematic constraints and several other factors such as Special Use Airspaces. The proposed path planner firstly expands obstacles according to RNP requirements. Then it rapidly explores the environment through modified RRTs to generate a feasible path. Finally the initial feasible path can be shortened by pruning and smoothing method for problems without kinematic constraints or by path optimization method for problems with kinematic constraints. The pruning method based on A* algorithm and smoothing method based on B-spline curves are presented herein. Numerical simulations are performed based on the airspace environment around Beijing capital international airport using the real standard navigation data. The simulation results indicate that the proposed path planner is able to generate a 3D smooth collision-free path that complies with RNP flight operation while considering the aircraft kinematic constraints.