Time-Controlled Aircraft Guidance in Uncertain Winds and Temperatures

The design requirements on airborne equipment which controls an aircraft so it arrives at an assigned time are mainly driven by the need for satisfactory control during descent. Assuming open-loop control during a typical descent, the final altitude and arrival time errors due to unforecast winds and temperatures aloft are determined. The fuel required for closed-loop control to reduce these errors is given. Equations of motion, suitable for on-board nominal descent trajectory computation using descent area forecasts, are derived, including the effects of winds and temperatures. A sample descent trajectory, obtained by integrating these equations with an actual forecast, is given. The design of descent controllers using feedback of errors relative to the nominal trajectory is treated. The arrival time errors and fuel usage of such controllers for different gain choices and unforecast winds and temperatures are evaluated by simulation.