Data Burst

Aimée Turner examines European efforts to salvage a crucial technological enabler of the Single European Sky and assesses the likely impact on the deployment momentum of this key building block
The platform on which Europe has established datalink – the cornerstone enabler for 4D trajectory flight – has proved technically impossible due to disastrous system overloads and potentially dangerous radio interference.
The European Aviation Safety Agency (EASA) which carried out an investigation earlier this year on behalf of the European Commission warned that despite some tweaks over the past six years, the ICAO Aeronautical Telecommunication Network (ATN) Controller Pilot Data Link Communications (CPDLC) remains far too vulnerable due to the system dropping out at ten times the acceptable level of safety.
The European region is the first to use the ATN datalink solution after the FAA in 2004 abandoned their ATN plans and decided on reactivating their Data Comm plan to go with the FANS version of CPDLC which uses ACARS. The EU regulation requires equipage with ATN CPDLC using ICAO VDL mode 2 technology – the same system used without all the complexity of the ATN layer for enhanced ACARS messaging by airlines.
The VDL design specifies a common signal channel for network management and the first radios deployed had to provide service on that channel. The design allows for adding more radios providing service on distinct channels for data transmission as traffic increases.
When the various independently developed systems started trying to communicate and as the number of equipped aircraft ramped up to comply with the mandate, the gaps in ATN became apparent. Differing interpretations in implementing the ATN and VDL protocol have caused lots of ‘aborts’ of logical connections cutting off communications, which has proved to be the Achilles heel of European datalink. .
databurst“When bandwidth is constrained, problems will first materialise in the ATN datalink,” noted EASA, adding that the many ground stations at airports supporting ACARS only exacerbates poor connectivity due to radio interference.
Questions are now being asked over which agency has the competence required to approve corrections to the avionics implementations of ATN and VDL that will stop the connection aborts.
It is something which critics of European datalink suggest would have been foreseen had an organisation with regulatory authority been charged at the outset with testing or approving the way the new ATN avionics worked with the supporting networks.
In fact, datalink technology is so far from meeting its availability targets on the basis of a relatively small number of the European equipped fleet that Brussels chiefs believe they have no option other than to pull the rollout for several years until a more robust multi-frequency infrastructure is developed.
Five Years
The reality is that while many of the organisations subject to European datalink regulations have deployed the required elements, the full operation of CPDLC is now going to be around five years later than scheduled.
“Datalink is the first really hard part of the new generation ATM system that Europe has attempted to implement,” says Philip Clinch, VP of aircraft services at SITA. “It has not been clearly recognised how difficult it is to make all work together ANSP systems, shared data radio networks and airborne systems as well as the controllers and pilots.”
So what’s next? At an October 9 workshop, the Commission convened the various industry actors to help hammer out an alternative implementation framework consisting of a two-step approach that tackles both technical and legal issues.
On the technical side and as recommended by the EASA report, the European ATM research and development effort SESAR will investigate what is wrong with the radio frequency environment, the potential for a multi-frequency VDL mode 2 implementation and possible improvements to the ground radio infrastructure. SESAR will then be responsible for coming up with some tested solutions which will probably take anything up to four years.
In parallel to that, and until such validated solutions are known and reflected in a new updated legal framework, it will be necessary to suspend the current legal mandate for airlines and air navigation service providers (ANSP) to have all the necessary kit installed to be datalink-ready.
databurstThat would effectively postpone the equipage requirements by European airlines by a minimum of five years although at least that revised date would apply for both forward fit and retrofit. As for the ground implementation, the foreseen postponement would be limited to three years which would at least ensure that there is eventual Europe–wide availability.
So what do European air navigation service providers who have already invested in ATN systems and VDL stations and who have deployed the national elements of the required pan European ATN/VDL network do now?
While airlines such as Ryanair which have invested heavily in deploying datalink technology want a clear plan to ensure a return on investment, the attitude of those providing air navigation services seems relatively sanguine.
Sandra Peter for the Civil Air Navigation Services Organisation (CANSO) told the workshop that while the two-year difference between the legal obligation for the ground and for the airborne was of concern, those ANSPs that had already deployed it were happy enough to busy themselves with continuing to trial datalink.
Wrong Choice
The European Commission in an exclusive briefing for Air Traffic Management argues that it was Eurocontrol that was originally supposed to have managed this kind of network-wide initiative and that, over and above a lack of an adequate management, Eurocontrol and industry may simply have made the wrong technological choice – mainly driven by French interests.
Even so, during the later SESAR-driven deployment phase that was accompanied by a swathe of regulatory packages, the Commission established a group of experts known as the Interim Deployment Steering Group (IDSG) in 2012 to help smooth the early days of the rollout of advanced Single European Sky technologies.
Its role was to steer the implementation of short term essential deployment activities identified as critical to further future deployment under SESAR. The Interim Deployment Programme included air-ground datalink as one of seven activity areas and the IDSG was specifically tasked to monitor the implementation of datalink regulation.
databurstThe Commission further argues that the so-called SES Interoperability Regulations that were all adopted between 2006 and 2012 contained no specific provisions for a high-level management task to be attributed to any organisation, nor did they include precise implementation monitoring provisions.
“When they were adopted, on the basis of very wide consultation of all stakeholders, and with the favourable opinion of the Single Sky Committee members, the need for such ‘overarching management/monitoring’ was probably overlooked or was not deemed necessary, and in legal terms, the respective parties whether operators, air navigation services providers or the member states were ultimately responsible for the implementation of those parts of regulations under their responsibility,” said the official.
So was the regulation on datalink services simply too complicated because it required ANSPs to acquire CPDLC systems at the same time as new air-ground networks shared with airline communications were being deployed – in addition to the fact that airspace users were being required to install new avionics complying with ICAO ATN standards that had never previously been implemented operationally?
The four-year period of preparation which was dominated by intense consultations among all stakeholders and by lengthy debates in the Single Sky Committee demonstrates that achieving a synchronised deployment of capability on both the ground and in the air was actively acknowledged as being a hugely complex affair.
“It was the first time, in the aviation sector, that a regulation affecting both air and ground was being discussed and adopted,” said the official. “At that time however, the referred standards including ICAO ATN standards with its constraints and limitations were known to all stakeholders. Datalink had also been deployed operationally notably by Eurocontrol at the Maastricht Upper Area Control Centre since 2001 and further validated during many years in the context of the Link2000+ programme.”
Even so, was it ill-conceived for the Commission to have expected that ATN CPDLC operations would go without any hitch once all the various stakeholders flicked their respective switches?
“At the time of adopting the regulation in 2009, there was neither indication nor precise information by stakeholders that the referred technology and standards would not work when switched, especially after more than 10 years of standardisation work, research, development and validation programmes run on those technologies,” said the official.
databurstSo why was it that no organisation with regulatory authority was charged with testing or approving the way in which the new ATN CPDLC avionics worked with the supporting ATN/VDL networks despite the fact that they are the first operational implementation of the ICAO ATN standards anywhere in the world?
Brussels points out that as regards individual avionics elements, EASA is in charge of certifying the required avionics based on the necessary standards. “More specifically as regards the conformity of constituents and systems and the verifications of systems, specific provisions of the regulation were adopted, in line with the generic ‘conformity assessment’ provisions of the Interoperability Regulation,” says the official.
SITA’s Clinch says that over in the United States where the Federal Aviation Administration is implementing its own equivalent datalink programme, the agency avoided these problems when it signed up Harris Corporation as a Data Comm Integration Services provider to integrate the required network service, work on avionics incentives and overall system testing.
Clinch points out that the Eurocontrol Centralised Services proposal has drawn attention to the benefits of having a pan European VHF datalink network to provide the services needed by CPDLC communications, something which the Commission agrees needs further investigation if better coordination of ground infrastructure is to be achieved.
Here, Eurocontrol’s director-general Frank Brenner tells Air Traffic Management that there would indeed be a very real advantage in having central mechanism to manage this area. “That’s why we have proposed such a service: the CS 9-2. This is currently progressing through a feasibility study and we will be discussing shortly with our member states how to take it forward.”
While many onlookers admit to a certain grim fascination at how all these factors will converge to create the semblance of an adequate framework, one of the principal lessons learned is that – given the complexity of the datalink community – an end-to-end validation, ideally with large scale demonstrators, followed by comprehensive implementation monitoring and management should have been central to the plan from the outset.
This could have prevented the architects of Europe’s 4D vision from wasting vital time and certainly the resources of a cash-strapped industry that still has to be convinced over the timely merits of one of Europe’s flagship projects.