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Flight Path Monitoring - Ground Supported Navigation |
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For the 4D ATM philosophy to be successful it was foreseen that non-4D equipped aircraft must be supported in their navigation. Whereas 4D equipped aircraft are generally able to cope with deviations from their planned trajectories that are due to modelling errors in their Flight Management System (FMS) or unexpected meteorological conditions, non-4D equipped aircraft are not. Together with the fact that a significant part of the total fleet of aircraft will not be equipped with 4D FMSs between the timeframe of the PHARE experiments and the year 2015, a ground supported navigation function to assist non-4D FMSs aircraft was required.
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The PHARE Demonstration 3 Flight Path Monitor (FPM) was able to provide ground supported navigation for non-4D equipped aircraft in the longitudinal direction, by providing calibrated airspeed (CAS) advisories. A non-4D equipped aircraft, is one that is able to fly its planned trajectory in 3D space but is not always able to meet the time constraints on these points.
The FPM Ground Supported Navigation (GSN) function is explained below.
The Flight Path Monitor GSN function is initiated either when medium longitudinal deviations occur or when meteorological information has been received that shows that significant changes have occurred in the meteorological conditions along the considered trajectories. Once the Ground Supported Navigation function is initiated, a number of checks are done in order to evaluate whether it is useful to start the calculation of an advisory. Checks are made on:
- The availability of meteorological information.
- The aircraft equipment.
- The feasibility of the segment for which the advisory will be calculated.
- The utility of advisories for that flight.
- The existence of a previous advisory for that flight and segment.
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A segment is a part of the System Plan for which there is a constant CAS regime. Its first and last System Plan point, the (constant) flight mode, and the CAS value define a segment. A segment is deemed not feasible if, for example, the time difference between the start point and the end point of the segment is too short to calculate a corrective advisory.
The outcome of the Flight Path Monitor Ground Supported Navigation function is either no advisory, a CAS advisory, or a replan advisory. No advisory is returned when the FPM predicts that the longitudinal deviation will not become too large for the considered segment assuming that the aircraft maintains its original CAS during that segment. A CAS advisory is returned when a feasible CAS value (other than the original CAS value) has been calculated.
Such a feasible CAS implies that the Flight Path Monitor has predicted that the aircraft will not deviate too much in the longitudinal direction for the considered segment, if the calculated CAS advisory is followed. From all possible values for the desired CAS, the one that is chosen is the one that differs the least from the original CAS value.
Besides the value for the new CAS, some other information is also returned. This information includes the flight ID and the segment where the CAS advisory is to be followed, the time and position that the CAS advisory has to be given by the controller, and the point until which the advisory applies.
A replan advisory is returned when the Flight Path Monitor predicts that, at the end point of the segment, the deviation of the aircraft will be so large in at least one direction that no feasible corrective CAS value can be determined.
Both the Trajectory Predictor and the Ground Human Machine Interface can use the output of the FPM GSN function. The Ground Human Machine Interfacecan present the advisory to the controller (at least when the advisory is a CAS advisory) and the Trajectory Predictor can generate a new feasible System Plan in response to a replan advisory.
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