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Further details on the Experimental Flight Management System
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The potential efficiency of such approaches to Air Traffic Management requires that it be possible to check trajectories against each other to identify any conflicts between them. An aircraft following an agreed trajectory can then be assured a trouble free and unperturbed flight.
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| Illustration of a user preferred trajectory (Click for larger image) |
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Preferred trajectories from several aircraft will inevitably lead to conflicts which must be resolved by constraining one or more aircraft to fly a non-optimum trajectory. Such traffic avoidance constraints may occur at any point in a trajectory and may involve changes to the lateral track, to altitudes or to timing. The aim is to modify an optimum trajectory as little as possible whilst still meeting the necessary constraints.
Within PHARE trajectory prediction was carried out both on the ground and in the aircraft. The PHARE Advanced Tools Trajectory Predictor was a ground-based tool which could generate aircraft trajectories for both the controller and other assistance tools. The PHARE concept was also based on the aircraft defining their own preferred trajectories (using internal trajectory prediction software) from constraints sent from the ground ATC system. This preferred trajectory was then sent to the ground system so that the controllers could ensure that separation standards were maintained.
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Airborne Trajectory Prediction |
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A trajectory in PHARE Demonstration 2 (Click for larger image) |
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The PHARE Experimental Flight Management System enables a range of real and simulated aircraft to take part in ATM experiments involving the exchange by datalink of detailed constraints from Air Traffic Control and predicted trajectories from the aircraft. The Experimental Flight Management Systemhad a number of mechanisms which allowed the prediction of nearly optimum trajectories in the presence of traffic avoidance constraints provided by the controller.
The basis for the Experimental Flight Management System modification process was the definition of an optimum flight in a suitable way for controlled modification. This was done by means of a Phase Table which described the typical flight in terms of a series of subphases from takeoff to a level approach to ILS intercept.
The route which the aircraft is to fly is described by a Constraint List based on a series of waypoints. This structure was also used in uplinks from ATC to specify constraints on the flight. Meteorological forecasts were used to build in the effects of wind and temperature. The performance of the aircraft was simulated by a specific model which provided information about thrust and drag with the aircraft flown as described in the phase table. The modification process worked with the above inputs to arrive at a trajectory prediction which was as close as possible to the original phase table but met the constraints.
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The PHARE Advanced Tools Trajectory Predictor |
The main role of the PHARE Advanced Tools Trajectory Predictor was to support the ground controllers in their manipulation of constraints, allowing them to model and assess the effect of their actions prior to modified constraints being sent to an aircraft. Additionally, the tool could generate trajectories on behalf of 3D aircraft.
The Trajectory Predictor provides the following services to support the PHARE Advanced Tools:
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Calculation of optimal 4D trajectories, from the aircraft current position to the last position on the planned route. |
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Generation of tubes relating to a trajectory which were used by the Flight Path Monitor to confirm an aircraft is following the agreed trajectory. |
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At the core of the PHARE Advanced Tools Trajectory Predictor was the Experimental Flight Management System (EFMS). The air-based trajectory prediction software was modified to make it suitable for use within a ground based system.
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The method for optimal prediction of trajectories is described in:
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