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: The invention is described in the environment of a binary data magnetic recording and reproducing system and comprises a binary to non-consecutive zero code converter for encoding the input binary data into a non-consecutive zero code which, in turn, is recorded on the magnetic medium. In recording, a flux transition occurs for each ONE of the non-consecutive zero code. A bipolar peak detector detects the flux transitions and thus detects the presence of the recorded ONEs. The peak detected signals are utilized to continuously trigger a mono-stable multivibrator having a period whereby the multivibrator relaxes to its stable state in the absence of a ONE which denotes the presence of a ZERO. The peak detected signal and the output of the mono-stable multivibrator are utilized to synthesize a clock signal from the recorded non-consecutive zero data.