NATS is working with European partners to help predict aircraft flight paths more reliably, which will in turn improve the accuracy of potential conflicts as they are displayed to air traffic controllers (ATCOs) and help airlines adopt the best available routing to maximise environmental benefit and reduce costs.

4D Skyways is a pan-European SESAR project researching trajectory management solutions that could enable greater automation in air traffic management (ATM) tools.

Currently our systems on the ground predict live trajectories of airborne aircraft for conflict detection purposes. These ground-based tools use pre-calculated data to generate trajectory information and, because of the uncertainty in the input data, inevitably these trajectories also carry a level of uncertainty that limits the full benefits the tools can bring.

Many of the SESAR concepts being developed to improve ATM performance are underpinned by Trajectory-Based Operations (TBO), which offer a much higher-resolution view of a flight as well as a standardised method of exchanging and interpreting flight trajectory information. As part of the 4D Skyways project, we have been working to support the roll-out of TBO and enhance the planning and management of traffic flows.

The operational problem we have been working to address is the need for ATCOs to issue complex clearances for flights in vertically-constrained systemised airspace while proactively monitoring the planned vertical profile of an aircraft flying in these circumstances.

NATS and DFS are working with industry partner Indra to develop a common concept, requirements and prototype to develop conformance monitoring capabilities using downlinked aircraft ADS-C data. Once this prototype is ready, NATS and DFS will test it in parallel activities and different operating environments, with the aim of defining a concept that can be widely applicable to ATM operations across Europe.

NATS’ primary focus is conformance monitoring, which concentrates on aircraft following published ‘descend via’ or ‘climb via’ flight procedures, but will also include monitoring support for aircraft clearances to reach a waypoint above or below a certain flight level.

We completed detailed analysis to investigate possible improvements to trajectory prediction and conflict detection capabilities and ran several workshops with ATCOs to validate the usefulness and benefits of these potential changes; our results will inform future SESAR projects.

As part of our SESAR work we have also explored ways to make it easier and cheaper for stakeholders to implement TBO through a common service to provide flight trajectory information automatically and simultaneously to multiple stakeholders. A Trajectory Prediction Common Service (TPCS) would avoid the cost of implementing a separate data communications system for each stakeholder; in addition to developing the system architecture, we created a business model to show how such a service could fit into the ATM landscape alongside a SESAR-envisaged version of TBO.

Overall, our 4D Skyways research has established trajectory-based operations as a workable future solution that could significantly improve the accuracy of flight trajectory prediction and offer enhancements in the detection and resolution of potential aircraft conflicts.


The work described in this article has received funding from the SESAR 3 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement number 872320. The opinions expressed herein reflect the author’s view only. Under no circumstances shall the SESAR 3 Joint Undertaking be responsible for any use that may be made of the information contained herein.


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