Vertical path control for aircraft area navigation system

Abstract

In the vertical path control of an area navigation system when the aircraft ascends or descends to a waypoint with an 'at-or-above' or 'at-or-below' altitude requirement, vertical steering is effected at a constant airspeed with regard to a reference airspeed. An alert device is included to provide a warning to the pilot when the aircraft flight path angle is less than the straight line flight path angle to the waypoint for 'at-or-above' waypoints or when the flight path angle of the aircraft is greater than the straight line flight path angle to the waypoint for waypoints with an 'at-or-below' altitude requirement. Altitude error is displayed on a vertical deviation indicator of an aircraft flight instrument in accordance with the difference between the actual aircraft altitude and the altitude of the next waypoint having a firm altitude requirement. When the aircraft ascends or descends to a waypoint through the pressure-barometric altitude transition, flight path angles are computed and utilized as the vertical steering reference to avoid a steering discontinuity at the transition altitude. When the aircraft is on a descent path to a waypoint and an airspeed reduction is required, vertical angles are computed and utilized for generating the vertical steering signal whereby a speed reduction transition zone is included in the flight path to effect the speed reduction and make good the desired waypoint altitude.