New Approach

David Bowen, SESAR JU’s ATM chief, explains how Europe plans to fix the troublesome VDL Mode 2 datalink solution and outline an emerging performance-based vision for the future
The sorry history of the datalink technology which Europe so disastrously adopted is well documented, writes Aimée Turner.
Two years ago it was decided that the cornerstone enabler for 4D trajectory flight was technically unusable due to disastrous system overloads and potentially dangerous radio interference.
The European Aviation Safety Agency (EASA) which carried out an investigation into the issue on behalf of the European Commission warned that despite some tweaks to the technology, messaging between controller and cockpit using the Aeronautical Telecommunication Network was liable to randomly disconnect at ten times the safe level.
That meant that the technology was so far from meeting its availability targets when only a limited number of aircraft were using it, that its rollout was to be shelved for five years until a more robust multi-frequency fix was found.
The SESAR Joint Undertaking (SESAR JU) was tasked with studying the limits of VDL Mode 2 to identify what exactly needed to be done to deliver high-quality data communications capabilities, essential to achieve the efficiency and capacity improvements required by the Single European Sky.
It found that VDL Mode 2 over one single frequency had already reached its capacity limits and that a four-frequency implementation would be a minimum requirement to support its deployment until 2025 in high density areas.
The SESAR JU also launched what was referred to as the ELSA Consortium study – to examine the prevailing end-to-end VDL Mode 2 issues and to define potential technical solutions for multi-frequency deployment and possible VDL Mode 2 improvements. Conducted by a consortium of industry stakeholders, that study is about to be presented to the European Commission.
The ELSA Consortium report will essentially advocate that the operational period of VDL Mode 2 will be maximised. More importantly, the conclusions in that final report will address the shifting technology environment as it has become increasingly clear that the European datalink infrastructure will need to evolve over the next 15 years. That is due in large part to greater capacity and performance ambitions that were contained within the 2015 edition of the European ATM Master Plan and the SESAR 2020 work programme.

“If you take a step back and take a wider view on communication strategy, the next step should move away from a specific system focus”

David Bowen, SESAR JU’s ATM chief tells Air Traffic Management that the focus of the latest report to be delivered to the Commission will be on identifying the actions needed to fix the VDL Mode 2 system to make sure it meets the requirements and is fit for purpose with regards to the original datalink regulation.
While it is now widely agreed that VDL Mode 2 technology should have been developed for SESAR in a more timely fashion, ready for the 2009 datalink regulation, the report will feature a series of recommendations which will contribute to achieving not only the immediate but also the ongoing performance improvement of VDL Mode 2 to support the implementation for the first SESAR applications that rely on datalink such as flight trajectory data exchange.
It is foreseen that those recommendations will be more widely disseminated to stakeholders after the summer break and that by that time some effort will have gone into communicating that message in the most effective way.
More importantly the ELSA Consortium study will feature a new approach, one that puts performance at the fore. That will mean that in parallel to VDL Mode 2 which will need to be used until a certain time horizon, the plan will be transition towards a basket of other technologies.
“If you take a step back and take a wider view on communication strategy, the next step should move away from a specific system focus,” says Bowen.
“In terms of a communication strategy roadmap,  the step beyond VDL Mode 2 is one where we want to move away from a specific system focus and move much more towards a performance approach which addresses questions such as ‘what do you want to do with the datalink system?’ and then asks ‘which system meets your operational need or application?’.”
“So if an airspace user wants to take part in 4D trajectory operations, for example, where it would  need to exchange 4D trajectory information, that application comes with a certain set of performance criteria and there could be two or three links which could all meet that criteria.”
“That could be a satcom link, a terrestrial link, or perhaps other future types of link. From a ATM perspective we don’t want to worry what type of link it is. All airspace users need to know is that they have a link which meets the required performance which will allow them to take part in the application.”
One future terrestrial datalink technology on which SESAR is working – what will succeed VDL Mode 2 in the terrestrial domain and which looks likely to be a prime candidate within the ATM Master Plan and the ICAO GANP – is something called L-band Digital Aeronautical Communication System or LDACS.
This should support much higher data rates and performance than what VDL Mode 2 can offer which will likely be required for some of the advanced SESAR applications in the future. Preliminary work has been conducted here within the SESAR1 programme although solely at the level of breadboard prototyping.
“The idea is that we can get that up to a decent level of maturity in SESAR 2020 so we can have standards in place and move towards industrialisation,” says Bowen who adds that the likely timeframe for availability would be 2020-2030 for this technology.

“an airline will be able to pick its technologies depending on its type of operations and platforms and make use of whichever technology fits it best as long as it meets the need of the particular operation they want to do”

“The key principle here is that we are not looking to have the same traditional approach of making a technology available and then mandate it as we have seen that that does not work, it does not fit the airline business model and has created problems in a number of systems over the years where a similar approach has been adopted,” says Bowen.
“What we want to do is to decouple the performance we are trying to achieve from the systems that can support it so we are working on the development of datalink applications to support SESAR concepts which are consistent with the ATM Master Plan. We will look at the operations that can be supported, the information that needs to be exchanged and create requirements around that.”
Bowen believes there is already a clear path toward future satellite communications becoming more widely available and more widely used and points to the fact that even in the continental en route environment, Iris Precursor using Inmarsat’s SwiftBroadband connectivity will represent an alternative for those aircraft already equipped in a relatively short time.
“An airline will be able to pick its technologies depending on its type of operations and platforms and make use of whichever technology fits it best as long as it meets the need of the particular operation they want to do,” says Bowen. “So you may have two or three options in terms of physical datalink to be able to execute a datalink application.”
Iris Precursor
Bowen says it is something that will happen gradually although with Iris Precursor capability becoming available in the 2018 -2019 timeframe SESAR is looking at some demonstration activity within SESAR that could be used to support 4D trajectory operations.
“This will not negate any elements related to the existing mandate – which is a Commission responsibility – but in terms of technical options, even within a relatively short term you will have more options on the table that you could use in oceanic or continental airspace.”
Within the airport domain, Bowen says that for some of the high data intensity exchanges on the airport surface, there could also be a variety of options, pointing to the AeroMACS (Aeronautical Mobile Airport Communications System) which has been developed within SESAR1 but also technologies such as Wifi and GSM – not necessarily supporting air traffic services but some of the AOC’s high data load or some other non safety critical data requirements within the airport domain.
“So what you can see here is that we are gradually building a patchwork of options that you can use depending on your equipage and what you want to use it for,” says Bowen. “With the LDACS system we will be looking at maturing that technology during the period of the SESAR 2020 programme offering the ability to deploy in the 2020-2030 timeframe.”
“But that won’t be saying, right you have to pull out your systems and replace it with this, but saying, OK, what you now have available is a dynamic multi-link environment with three or four links available with varying performance characteristics.”
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