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: Apparatus for combining positional data from OMEGA and VOR/DME radio navigation systems to provide computed positional data corresponding thereto includes a circuit for generating an OMEGA compensation in accordance with the difference between the computed value of the positional data and the VOR/DME value thereof. The computed value is provided by algebraically adding the OMEGA compensation to the positional data from the OMEGA system. The gain of the OMEGA compensation circuit is adjusted in an inverse relation with respect to the range of the aircraft from the VOR/DME station thus providing high accuracy positional data throughout the enroute flight of the aircraft without the attendant complexities and inaccuracies normally associated with the separate OMEGA and VOR/DME radio navigation aids.