Modified Dubins parameterization for aircraft emergency trajectory planning

This paper presents a trajectory parameterization method for calculating emergency flight paths with variable airspeeds under conditions of constant wind. The method is based on the Dubins curve; however, it has been modified to allow for acceleration along the path and finite rate of change in turn rate. The aircraft's planar trajectory from an initial condition to a terminal condition is parameterized into a small set of path-defining variables. The method uses a number of closed-form solutions and simple iteration schemes to efficiently calculate a path that meets the specified constraints. The parametrized path can then be optimized to minimize a performance objective for real-time emergency path planning. For emergency flight planning, the vertical degree of freedom is treated as a function of the aircraft state and parametric controls, and the optimization is formulated to ensure touchdown at a desired location and aircraft state. The performance of the proposed method is investigated using several test cases, including landing of a commercial jet following total loss of thrust and autorotative recovery of a utility helicopter following total loss of power.