The aeronautical hazard is produced not by high wind speed alone but by high wind shear, the variation of wind speed and direction from one point and time to the next. In addition to continuing problems associated with crosswind landing and frontal shear, four disturbance types are of particular concern: microbursts, wind rotors, aircraft wake vortices, and clear air turbulence. Each of these has a different effect on aircraft dynamics, and our ability to predict and respond to encounters with them differs as well. Avoiding the encounter in the first place is the safest strategy, calling for improved methods not only of sensing hazardous phenomena but of guiding aircraft around them. Avoidance is not always an open option; for inadvertent encounters, reactive, feedback control must be employed to prevent incidents and accidents.
An optimal, "belt-and-suspenders" approach to safe flight involves an intelligent combination of prediction, guidance, and control, including cooperative efforts between aircraft and the air-traffic management infrastructure. We discuss the hazards and control strategies for minimizing them, including Bayesian belief networks for hazard prediction, optimal landing-abort trajectories, nonlinear-inverse-dynamic guidance, and LQG regulators for disturbance rejection.
(Robert Stengel is a Professor of Mechanical and Aerospace Engineering at Princeton University, a Fellow of the IEEE and the AIAA, a graduate of MIT and Princeton, former associate editor-at-large of the IEEE Transactions on Automatic Control, and North American Editor of the Cambridge University Press Aerospace Series. He is the author of Optimal Control and Estimation (Dover, 1994), and he is writing a book on aircraft flight dynamics and control.)