ATM Modernization, Commercial

Europe Moves on Datalink

By George Marsh | May 1, 2007
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The day when pilots and air traffic controllers in Europe can bid farewell to routine voice messaging — for sector handovers, ATC clearances and the like — is coming closer as datalink communications take hold.

This year, some 350 aircraft equipped with VDL Mode 2, the selected digital VHF datalink complying with ICAO’s Aeronautical Telecommunications Network (ATN) standard, will benefit from datalinked communications while traversing Europe’s densely congested airspace, and many more will follow. Operated by 15 airlines, these aircraft have been dubbed "pioneers" under Eurocontrol’s Link 2000+ datalink program.

On the ground, controllers less engaged in communicating with pilots will be able to handle more traffic. Eurocontrol expects Link 2000+ to boost traffic-handling capacity by 11 percent in core airspace by the time all the relevant Air Navigation Service Providers (ANSP) are equipped for Controller Pilot Data Link Communications (CPDLC) and 75 percent of all en-route flights are made by CPDLC-equipped aircraft.

A major milestone expected this year is the final ratification of an Implementing Rule (IR) for the datalink. At this writing, Eurocontrol was about to enter a formal consultation with all stakeholders on a draft rule formulated by its regulatory unit. A two-month consultation period, which began in March, should lead to final agreement on the service to be provided under Link 2000+, on the VDL Mode 2 datalink technology needed to support it and on implementation dates.

A workshop has been set for June to finalize a package that can be sent to the Single European Sky committee of the European Commission. After the EC has carried out its own vetting process, Eurocontrol anticipates the implementation rule can become effective by the end of the year.

"This will be highly significant because the rule will help us to synchronize implementation of datalink in the air and on the ground," said Martin Adnams, Eurocontrol’s Link 2000+ program manager. "All the relevant dates will be there and the agreement will be binding on aircraft operators and Air Navigation Service Providers."

Indications for agreement on the datalink service are positive. Unofficial soundings with the Joint User Requirements Group of the International Air Transport Association suggested the proposed implementation dates "can be lived with," provided the ground side is readied on time.

Equipage incentives

The IR will clear the way for mandates that aircraft flying through core European airspace at Flight Level 285 or higher must be VDL Mode 2 equipped for CPDLC operations, and that some 15 control centers on the ground must be equipped to support datalink service.

However, Eurocontrol is applying a more subtle approach to equipage than this suggests, seeking mandates as a last stage in an extended process that also includes a funding-assisted pioneer phase and an incentivization phase to stimulate early airborne equipage.

The first 15 airlines to equip, the so-called pioneers, have done so with a degree of financial subsidy. Eurocontrol provided some 20,000 euros ($26,400) per aircraft for about half of the 350 aircraft. The subsidy has been the same irrespective of aircraft type or airline, even though actual cost varies widely depending on whether the installation is new or a retrofit, the type of aircraft, its age and certification requirements. Further direct funding recently was discontinued once the funds set aside by Eurocontrol for this purpose had been spent.

The pioneer datalink operators are Scandinavian Airlines, American Airlines, Airbus Transport International, Air Europa, Air Berlin, FedEx Express, Lufthansa, Hapag-Lloyd, Finnair, Aeroflot, Alitalia, LTU, Niki, Malev and Lufthansa City Line. Already between them, the airlines are generating more than 200,000 CPDLC flights per year.

Link 2000+ is due to transition from the pioneer phase to the incentive phase at the end of 2007. Implementation will then be further encouraged using alternative funding sources, and perhaps later by allowing route-charge credits for equipped aircraft. This will be justified to other airspace users by the fact that such aircraft place less load on the ATC system.

Further formation of a critical mass of pilots, controllers and engineers will be encouraged by the operating experiences of the pioneers.

For a start, enabling pilots and controllers to work less hard at communications saves time and reduces fatigue. There is reduced voice channel congestion, and misunderstandings that commonly mar voice communication are avoided. Flight crews will have to log on once for a flight across Europe, with the datalink parameters passed on to successive control centers automatically as the flight proceeds.

Many pilots are favorably inclined to datalink already, being familiar with the benefits of the less capable but established Aircraft Communications Addressing and Reporting System (ACARS). Having clear and retrievable messages delivered in a timely and unobtrusive manner has strong appeal for them.

"Once they have seen the system in action, pilots want it as quickly as possible," Adnams said. "…The pioneer scheme has been highly successful and has provided the kick-start that datalink needed."

Officials expect improved ATC efficiency to result in fewer delays, better flight profiles and better-optimized use of airspace. Safety gains should result from reduced workload, fewer misunderstandings, the presence of a second communications channel and the ready availability of a voice channel for urgent communications. Controllers can see which aircraft are datalink equipped and which are not, and can communicate with the latter by VHF/voice in the traditional way.

‘Softly, softly’

Eurocontrol’s progressive introductory process was devised after lessons learned with previous implementations, in particular reduced vertical separation minima, 8.33kHz VHF channel spacing and Basic Area Navigation — cases where a mandate for change typically was followed by a long wait and then a last-minute rush to install the necessary equipment.

Under the organization’s "softly, softly" approach, much of the 75 percent equipage needed to produce the initially expected 11 percent ATC capacity gain is likely to be achieved during the pioneer and incentive phases. Nevertheless, it is expected mandatory equipage will be necessary to secure the full benefits.

A 14 percent improvement is calculated if all aircraft using Europe’s upper core airspace could be equipped, but exemptions for older aircraft plus military and state aircraft will prevent this from being achieved in practice. Mandatory equipage would apply from 2009 for new airframes (forward fit) and by 2014 for older aircraft (retrofit).

In terms of ground infrastructure, the Maastricht Upper Air Control Center (MUAC), which controls Europe’s busiest en-route airspace over the Benelux countries (Belgium, the Netherlands and Luxembourg) and northwest Germany, is blazing a trail, having upgraded to the necessary datalink standard in 2003. Since then, the center has used CPDLC extensively to interact with aircraft equipped with ATN/VDL2.

The MUAC center also accommodates the Future Air Navigation System (FANS) standard for GPS positioning to boost the numbers of aircraft with which it can conduct CPDLC operations. There were 26,253 CPDLC transactions during 2005 and 51,754 in 2006. Adnams predicts a quadrupling of the 2006 number this year as all the pioneer aircraft become operational.

Lessons learned at MUAC will help other control centers and ANSPs avoid operational and technical pitfalls that seem inevitable in the early adoption phases of a new technology.

Under "CPDLC 2008," a subsidiary activity within Link 2000+, a support team will advise on technical aspects, including baseline equipment, front-end processor requirements, whether to implement VDL-2 as an in-house effort or to contract the task to an outside supplier (in practice this would be SITA or ARINC), and implementation of ground-to-ground, on-line data interchange and system testing.

The team also will help with development and harmonization of procedures, human factors, demonstrations for staff, hand-over procedures, certification and safety case development. As operational experience grows, lessons learned will be shared with all datalink implementers via a web-based repository.

Ground implementation at the 15 area control centers was progressing slower than Eurocontrol wished. ANSPs DFS, of Germany, Skyguide of Switzerland, ENAV of Italy, and possibly IAA of Ireland look to be the first wave of providers due to start implementing the datalink technology next year. Germany, as the most significant territory bordering the Benelux countries covered by MUAC, will be a particularly welcome addition.

Other air navigation providers — NAV of Portugal, DSNA of France, NATS of the United Kingdom and AENA of Spain — are targeting 2010-2011 for implementation. Although Eurocontrol does not view a two-stage implementation as ideal, the IR should at least ensure that datalink service is available across the whole of the Link region by 2011.

CPDLC is just one of a range of new technologies and tools that will be required if air traffic management is to keep pace with Europe’s burgeoning demand for air travel. Eurocontrol is backing the ATN/VDL2 datalink because saturated frequencies and reliance on voice for pilot-controller communications represent a major bottleneck.

The new datalink puts extra capacity into the system and eases the pressure on high-density airspace. As Eurocontrol sees it, the R&D has been done, the standards are stable and the business case justifies the system. Results from operation over nearly four years at Maastricht have demonstrated its fitness. Link 2000+ is expected to take the program to fruition.

Future applications

The CPDLC applications chosen so far are considered the most immediately affordable and productive, but once the datalink is in place more can be done.

A prime role of Eurocontrol’s Cascade program, a successor to Link 2000+ that will coordinate the implementation of Automatic Dependent Surveillance-Broadcast (ADS-B), is to exploit and expand that capability. Its full scope is explained by spelling out the acronym — Cooperative Air Traffic Services through Surveillance and Communications Applications.

Deployed within the European Civil Aviation Conference group of countries, Cascade is expected to further migrate pilot-controller communications from voice to data by growing the range of available pre-formatted messages from the present baseline of 63 (uplink) and 26 (downlink).

Enhanced CPDLC will include provision of airport-based services such as Datalink Taxi Clearance (D-TAXI) and Datalink Operational Terminal Information Services (D-OTIS). Again, as with Link 2000+, a graduated approach to implementation, involving pioneer and incentive phases before mandates, will be adopted.

Cascade eventually will enable the sharing of air traffic information so pilots can assume greater responsibility for maintaining separations, easing the task of ground controllers and freeing them to handle more traffic.

Utilizing Mode S datalink as well as ATN/VDL2, it will address some of the deficiencies of existing radar coverage by supporting implementation of initial ADS-B. Eventually, it will facilitate cooperative air traffic services, including graphical trajectory negotiation.

Led by Program Manager Alex Wandels, who previously led the Link 2000+ effort, Cascade already is conducting trials.

Glimpses of a datalink-enabled future are being provided by other forward-looking trials. In January 2006, SAS showed, on a revenue-service B737-800, how the flight crew and air traffic controllers can negotiate a near-optimum flight path from takeoff to landing, using datalink (the Aircraft Communications Addressing and Reporting System for the purposes of the trial). The flight profile included "green" approach (Standard Terminal Arrival Route, or STAR), in which time-of-arrival closely matched ETA.

A precise four-dimensional trajectory calculated in the Smiths Aerospace flight management system was downlinked to the ground controller, along with an accurate ETA. An agreed trajectory, allowing for any controller amendments needed for traffic deconfliction, was then uplinked back to the aircraft, which subsequently flew the defined flight path.

The B737 was equipped with a Rockwell Collins multimode VHF radio that was able to support not only ACARS and VDL2, but also the VDL4 datalink standard developed in Sweden. On the ground, LFV, Sweden’s ANSP, used its Collaborative Information Exchange System information-sharing tool. The flight was undertaken as part of the North European ADS-B network program.

Knowing the ETAs of all flights to within seconds, future controllers will be able to rationalize traffic flow by accelerating or slowing aircraft in the air, or holding them at gates, so that fuel and time wasted resulting from in-flight vectoring and holding are minimized.

SAS could reduce its annual fuel burn by 28,000 tons from green approaches alone, according to Lars Lindberg, of aviation consultancy Avtech. Carbon dioxide emissions would fall by 90,000 tons and nitrous oxide by 315 tons.

CPDLC Equipment Needs

Airborne components required for Controller Pilot Data Link Communications (CPDLC) include a VDL Mode 2 VHF data radio along with a communications management unit (CMU) and a printer. The radio requires a transmit/receive antenna, separate from the VHF voice radio antenna. The Rockwell Collins CMU 900, Honeywell Mk 2 CMU and Airbus Air Traffic Services Unit (ATSU) have received certification for VDL Mode 2 operation.

In retrofit situations, a human-machine interface can be achieved by modifying a multifunction control and display unit or by providing a dedicated keyboard and printer. Some datalink clearance services, for instance those including waypoints, may require inputs from the flight management system.

The existing flight deck audio and visual alerting system should be modified to alert the flight crew to the arrival of messages. Finally, software to support Link 2000+ services must be installed, normally as an upgrade to the existing CMU or ATSU. The software encodes and decodes CPDLC messages, as well as Aeronautical Telecommunication Network (ATN) system protocols.

Upgrade requirements on the ground consist of an ATN router and a front-end processor. These convert messages selected from menus at the controllers’ workstations into the correct protocol and routes them, via VHF transmit/receive ground stations, to the addressed aircraft. The process is reversed for messages downlinked from the aircraft.

Both SITA and ARINC provide the necessary ground station upgrades to support their VDL Mode 2 communication services. Multi-stack ATN/FANS gateways at Maastricht permit both VDL Mode 2 and FANS datalink operation. Other ANSPs will be able to decide individually whether they will provide service for both datalinks.

Airlines opting for SITA ATN service in Europe include FedEx (15 A330s), Lufthansa (20 A320s), Hapag Lloyd (20 B737s) and Air Europa (19 B737NGs). ARINC has been selected by SAS (20 B737NGs) and American Airlines (13 B767s), among others.

Pioneer SAS achieved datalink certification in December 2003 with an initial installation on a Boeing 737-683. The airline has progressively equipped 20 of its B737NGs with the necessary avionics, including VDL Mode 2 and ATN core software. Air Europa flew its first operational flight using CPDLC on one of its B737-800s in November 2005.

Over the last 18 months, Eurocontrol supported pioneer airlines in a range of activities including certification at its Bretigny test facility of an Air Europa B737-800 retrofitted with a Rockwell Collins CMU 900, certification with EAD Aerospace of an Alitalia MD-80 aircraft fitted with a Collins CMU 900 and interoperability testing of Airbus FANS-B ATSU software prior to certification on a Finnair A320. — George Marsh

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