European datalink crippled by ATN capacity show-stopper

The cornerstone enabler for 4D trajectory flight appears to be technically impossible due to disastrous system overloads and potentially dangerous radio interference, writes Aimée Turner.

The European Aviation Safety Agency (EASA) which carried out an investigation into datalink on behalf of the European Commission warns that despite some tweaks over the past six years, messaging between controller and cockpit using the Aeronautical Telecommunication Network remains far too vulnerable as the system is liable to randomly disconnect at ten times the acceptable level.

The Commission is now warning that because the datalink technology is so far from meeting its availability targets despite only a limited number of aircraft currently using it, it is recommending that its rollout is delayed several years until a more robust multi frequency infrastructure is developed.

“The Commission should arguably have investigated why the Eurocontrol process was not working but this will at least have the benefit of bringing the issues out in the open”

The European datalink solution is based on ICAO VDL mode 2 technology – also used for enhanced ACARS messaging by airlines – and requires an adequate number of frequencies to handle data volumes. The original design anticipated a common signal channel for network management and distinct channels for data transmission although only one channel was ultimately developed.

“When bandwidth is constrained, problems will first materialise in the ATN datalink,” said EASA, adding that the many ground stations at airports supporting ACARS only exacerbates poor connectivity through radio interference.

Philip Clinch, SITA’s VP of aircraft services, blamed a community wide underestimation of the complexity of implementing datalink over ATN as it has only ever gone through small scale trials using avionics with protocols implemented on a best efforts basis without an acceptance process by the air navigation service provider (ANSP) community. “The Commission should arguably have investigated why the Eurocontrol process was not working but this will at least have the benefit of bringing the issues out in the open,” he said.

“It is too early to conclude on the delay in implementing this technology. For the time being we expect at least a couple of years of work to fix technical problems”

Air navigation safety agency Eurocontrol tells Air Traffic Management that a multi-frequency approach would have been more secure, something it recommended over ten years ago, adding that it welcomed the Commission’s more proactive role on this.

News of the delay will come as an embarrassing climbdown by Europe which wanted datalink standards to be developed faster than its counterparts in the US, protesting that it needed to develop datalink to support 4D trajectory operations before SESAR’s 2018 target date as set out in the European ATM Master Plan.

A compromise was eventually struck that agreed a two stage standard-setting process that would allow for future applications once sufficiently mature. Now, Europe risks falling behind the US in its implementation of datalink.

“It is too early to conclude on the delay in implementing this technology. For the time being we expect at least a couple of years of work to fix technical problems,” confirmed the Commission.

Meanwhile recent datalink flight trials by EasyJet, Air France and Scandinavian Airlines across Italian and UK airspace as part of the AFD Consortium which includes NATS, Airbus Boeing, SITA and Selex and led by ENAV as part of the SESAR programme have demonstrated  increasing confidence about the use of datalink.

“KLM’s opinion is that the early equipage with [datalink] has been a useless investment because of the lack of ground service and of the technical problems”

Criticising the speed at which problems were identified, EASA is recommending that the future Deployment Manager would be best placed to roll out datalink, noting too that manufacturers of both aircraft and VHF radios will also likely to have to adapt their systems which could mean extra cost for airlines.

Indeed, Dutch carrier KLM which operates 100 equipped aircraft reports that disconnections struck randomly – mostly on its 737 NG fleet – during all phases of the flight, regardless of message or service requested. “KLM’s opinion is that the early equipage with [datalink] has been a useless investment because of the lack of ground service and of the technical problems,” it said.

Eurocontrol said it agreed that deployment should be more actively managed than was envisaged in the 2009 implementing rule and pointed out that it is evaluating whether a more central deployment and operation of datalink would benefit as part of its Centralised Services concept.

Clinch reckons any solution will likely come from those ANSPs that have already deployed VDL networks, merging them to create a European VDL service provider able to control all usage and approve pan-European implementation.

Andrew Charlton of the Aviation Advocacy consultancy comments: “Now is the time for leadership. The Commission should refund the amount spent by the airlines, and to be fair, by those few ANSPs that complied with the mandate, and we should agree a common, interoperable system across the Atlantic. Yes, that might see some delays, and some backtracking, but there is no forward tracking available, other than almost certain litigation and tears.”

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