Thrust laws for microburst wind shear penetration

Abstract

Two thrust guidance strategies have been developed and analyzed for the ability that they give aircraft to safely penetrate microburst wind shear during landing approach. These are used in conjunction with a pitch steering strategy that has already been shown to give improved performance by maintaining nominal glide path in the presence of microburst winds. The strategies provide valuable understanding of good thrust policy in a microburst. One of the two strategies is to control the airspeed to its nominal value, and the other strategy is to control the airspeed or the inertial speed, which ever is smaller, to the nominal value. To evaluate these strategies, a simplified 1st-order aircraft model has been used. Headwind/tailwind and downdraft microburst models have been considered separately. The safe-performance limits with respect to ability to track glide path have been plotted and compared with those for optimal trajectories. The thrust laws' performance limits are not as good as those for optimal trajectories, as expected; the thrust guidance laws cannot use the global knowledge of the wind field that the optimal trajectories use. Nevertheless, the ability of the practical strategies to safely penetrate severe microburst wind shear has been demonstrated. The best performing guidance law was that which controlled the minimum of airspeed and inertial speed to a nominal value. This demonstrates the importance of using thrust to keep the inertial speed at or above the nominal value. NOMENCLATURE