Wind-Aware Trajectory Planning for Fixed-Wing Aircraft in Loss of Thrust Emergencies

Loss of thrust (LOT) emergencies create the need for quickly providing pilots with valid trajectories for safely landing the aircraft. It is easy to pre-compute total lost of thrust trajectories for every possible initial point in a 3D flight plan, but it is impossible to predict variables like the availability of partial power, wing surface damage, and wind aloft in advance. Availability of partial power can affect the glide ratio of an aircraft while the presence of wind can significantly affect the trajectory of a gliding aircraft with respect to the ground, e.g. - a tailwind or a headwind can aid or hinder straight line glide by increasing or decreasing the ground speed. Wind can also change the shape of turns from circular to trochoidal, moving an aircraft away from its intended position. In this paper, we present a robust trajectory generation system that can take these dynamic factors into consideration. Our approach outputs valid trajectories to a target runway in the presence of constant, horizontal wind, by using purely geometric criteria for computing flyable trajectories. We model the effect of wind on different components of a possible trajectory by taking into account the observed glide ratio of the aircraft (computed from actual flight performance data) and the horizontal wind vector. We also take into account the effect of wind on ground-speed, the effective glide ratio with respect to the ground, and the shape of turns to calculate trajectories to a virtual point in 3D space which can lead an aircraft to an actual target runway. We introduce an analytical approach for calculating the virtual point for trajectories with left-straight-left or right-straight-right Dubins path segments and a heuristic iterative approach for other cases. Our approach generates trajectories that can lead an aircraft from an initial configuration (latitude, longitude, altitude, heading) to a target configuration in the presence of a constant horizontal wind. In our experiments, the computation time for trajectories ranged from 40 milliseconds to 60 milliseconds.