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.

Abstract: Control apparatus for an aircraft area navigation system provides a vertical path control signal to cause the aircraft to ascend or descend along a helical surface as the craft executes a transition laterally from the inbound course to the outbound course of a waypoint whereby the craft attains the waypoint altitude when crossing the course bisector thereof while maintaining a predetermined vertical flight path angle when steered on a predetermined lateral course transition path.

Abstract: Control apparatus for an aircraft area navigation system computes a predetermined curved path from the inbound course to the outbound course of a waypoint or the inbound course to the next waypoint and provides aircraft steering signals with regard to the predetermined curved path. A bank angle bias command is applied to the apparatus for effecting transition from the inbound course to the curved path and is removed when the aircraft transitions from the curved path to the outbound course. Cross track and track angle error signals are generated with regard to the predetermined curved path for steering the aircraft thereon as the course transition is effected.