RESILIENCE: Loud & Clear?

Paul Ravenhill discusses what needs to be in place in an effort to develop resilient communications for a digital future

ATM appears to be on the cusp of a bright new digital future.

A digital future in which remote towers and virtual centres offer new ways of providing air traffic control. Central to this vision is the idea of services. Rather than vertically integrating all elements of ATC into monolithic area control centres, various data services will be provided to ACCs using System Wide Information Management SWIM).

These services will provide a common view of all the data necessary to provide ATC: for example, flight, surveillance, Meteo and CNS. These new services could be provided by new entrants and over a wide area – for example in Europe for a Functional Airspace Block (FAB), or an industrial partnership like Borealis covering several FABs or even across the whole of Europe by the Network Manager.

In the future, rather than host a raft of different systems, an ACC will contain a set of controller work positions that are able to subscribe to the services necessary to provide the ATC service for the designated airspace.

In working out how to deploy this digital future resilience needs to be uppermost in our minds – and we need to think about resilience in two ways. Firstly, resilience for an individual ACC in terms of how these data services are provided – do we achieve the necessary redundancy through multiple providers? Or through multiple instances from the monolithic provider? Does competition or regulation define the cost and innovation of these services?

But we also need to think about the resilience of the overall ATC service. A great advantage of subscribing to a flight service over SWIM is that the location of the controller work position is really rather immaterial. If one CWP isn’t available, a different one can subscribe to the same service and take over – even if it is in a different ACC.

The ability of a network of virtual centres to be reconfigured in terms of airspace designations in order to cope with the loss of an ACC, or perhaps even to cope with significant shift in air traffic flows as occur with geopolitical events such as the current situation in Eastern Europe is going to be a huge step change in the resilience of ATM.

Building on current success for ground comms

This digital virtual future requires new ways of thinking about connectivity. Consider the shift from a visual tower to a remote tower. You need confidence that the cameras and displays are able to replicate the controller’s view to enable the ATC service, but you also need confidence that ground-ground communications will be sufficiently robust to enable a continuous service.

The same is true for virtual centres – traditionally for most ACCs the Flight Data Processor (FDP) is in the same building as the controller work positions; but it doesn’t need to be so long as the communications link can support the service. It is not unusual for an air navigation service provider (ANSP) to have one FDP supporting multiple airports (the so-called Hub and Spoke model) but the ground-ground communications will be very specifically designed around the operational requirements and may make use of bespoke communications protocols.

The connectivity required for virtualisation needs to be sufficiently robust so as to not be reliant on specific links or bespoke protocols and data formats. This form of digitalisation is well underway and bearing fruit in initiatives like AIXM and initial SWIM deployment.

It does require everyone to take cyber security seriously; but there are no show-stoppers. IP-based ground-ground networks (as power the internet) are used in many sectors such a banking, to provide secure services and can be procured from many third party telecommunications providers. Eurocontrol’s Pan European Network Service (PENS) demonstrates how collective bargaining can achieve price benefits and leverage the providers’ know-how for the benefit of ATM.

For ground-ground, the issue is to define service level agreements that support operational requirements without requiring costly specific add-ons for ATC. We should define the services we use around the available quality of service not pay through the nose for the additional continuity that no other sector seems to require.

Learning from the past for air-ground comms

Air-ground data communications is on the other hand by no means as clear cut – and is littered by historical problems caused by ATM’s desire to invent new solutions rather than adapt to what is already available.

What we have been learning from SESAR over the last decade is that it is environmentally much more efficient to allow an aircraft to define its own trajectory based on the minimum set of ATC constraints required for safety.

The initial idea of a precise gate-to-gate 4D trajectory is being replaced by new tools – like extended AMAN – that integrate the aircraft in to a sequence of arriving aircraft – that is, they deal with uncertainty in the trajectory where to do so at the least cost for the most benefit. For these tools to work, and to support demand capacity balancing, aircraft trajectories and ATC clearances will need to be synchronised across all ACCs and airborne systems. Without a new air-ground data communications infrastructure, digitalisation just won’t happen.

The solution is not resolving issues with VDL2 deployment. The quality of service required to support a digital future will require more in terms bandwidth, continuity, availability and timeliness than VDL2 was ever designed to provide. New datalinks are required; truly resilient air-ground communications are likely to require SESAR’s multi-link concept – where high performance requirements are met by multiple datalink working in concert, most likely one terrestrial and satellite link to reduce common modes of failure.

Solid progress is being made on a satcom solution. Inmarsat’s Swift Broadband safety service (SB-S) is being developed with the support of the European Space agency (ESA) IRIS programme and SESAR to achieve the emerging performance requirements – including the addition of extra security measures that just weren’t necessary when VDL2 was developed. IRIS is a great example of adapting a commercial offering to aviation’s needs. It also demonstrates that Inmarsat, as a commercial provider, is able to mobilise the necessary resources and finances to develop and deploy new technology. Kudos to them.

The positives from the satellite domain are made even more stark by the lack of progress on a terrestrial link. The original proposal from SESAR – a new L-band system referred to as LDACS stalled due to lack of clarity on requirements. A key goal of SESAR2020 must be to re-energise LDACS and ensure that a VDL2 replacement is available to support digitalisation.

But solving the datalink availability issue is only part of the problem – we need to learn from past mistakes and in particular the slow and fragmented rollout of VDL2. Successfully deploying complex distributed systems requires strong co-ordination – think about the Eurocontrol programmes of yesteryear – BRNAV, RVSM, 8.33 – they all succeeded due to strong programme management and really should set the ambition for the SESAR Deployment Manager.

As well as strong programme management, success will also need a better approach to regulation and standardisation. Current standards for ATC datalink cover the application, the network protocols and datalink in one or more documents. Applications operating over the FANS are not interoperable with those designed to operate over the ATN.

As we start to introduce new datalinks, shift to ATN/IP we need to rethink how datalink standards are written – separating applications, from network protocols and datalinks and defining performance requirements that enable aircraft operators greater flexibility to design a communications package that supports their connectivity requirements.

For a resilient future, let the competition in

Robust communications are the key enabler of a digital and more resilient ATM service. As citizens of the world we take mobile connectivity for granted; aircraft passengers are now often better connected to the outside world that the pilot is. Communications, and in particular air-ground datalink, is the weak link that could topple our virtualisation dreams.

PBN and GNSS already provide a strong basis for navigation for years to come – although a greater emphasis on the need for long term DME replacement as a terrestrial back-up would support increased residence. The core systems in GNSS – GPS, Galileo, EGNOS  – are not aviation-specific , they are multi-use constellations from which aviation benefits.

A combination of ADS-B and wide area multilateration (WAM) is able to provide a robust co-operative surveillance service – one that will be significantly strengthened when Aireon starts to provide satellite-based ADS-B. Aireon is another example of a commercial undertaking being able to mobilise resources for aviation’s benefit – it is hosted on Iridium which is a multi-use constellation.

Again and again, success in CNS is achieved where a commercial operator is able to leverage existing assets. IRIS is part of Inmarsat’s overall aeronautical service which is hosted on its network of geo-stationary satellites that support maritime and other safety and commercial services.

The aeronautical service, and in particular the IRIS enhancements to SB-S are only really possible because of the ability to make use of the existing space assets.

As in industry we need to learn from where we are to achieve a resilient future.

Paul Ravenhill is a director of UK-based ATM consultancy Think Research