Upgrading and Expanding Aircraft-Controller Datalinks Critical For Future ATM

As air travel roars back, with the International Air Transport Association (IATA) reporting that global airline traffic reached 88% of 2019 levels in March, there is a growing sense of urgency to increase the availability and quality of datalink communications between air traffic controllers and commercial aircraft.

This is especially the case since air traffic management (ATM) systems will have to account for new entrants, such as eVTOLs (electric vertical take-off and landing aircraft) and cargo-carrying drones, that will soon be sharing ever more crowded airspace. According to the Single European Sky ATM Research 3 Joint Undertaking (SESAR), the European public-private research initiative working towards a “Digital European Sky,” future ATM systems will need to provide “hyper connectivity” enabling wide-ranging data exchanges between aircraft and controllers.

“Of particular relevance is the improvement of datalink technology to dramatically increase capacity and reliability with reduced latency and addressing cybersecurity simultaneously,” Ruben Flohr, SESAR’s ATM expert for architecture and systems engineering, told Avionics International.

This goes beyond the pilot-controller text messaging that has largely been the main focus of the datalink efforts of air navigation service providers (ANSPs) over the last decade, he added, explaining that bringing an aircraft’s flight management system (FMS) into the communications loop is critical to maximizing air traffic efficiency.

“One of the most important changes from an operational perspective is the strengthening of the data exchanges between the on-board flight management system and the ground ATC system,” Flohr said. “This allows a more synchronized planning between controllers and pilots, such that both can more effectively anticipate the next steps.”

NAV CANADA Chief Technology and Information Officer Mark Cooper told Avionics International that “we are in a very exciting period as an ANSP and as an industry right now as customer needs, technological opportunities, and aircraft capabilities are changing. Many capabilities have moved from analog to digital.”

SESAR has identified four key areas where existing communications, surveillance, and navigation (CNS) infrastructure is challenged: rapid air traffic growth, spectrum constraints, cybersecurity, and new entrants such as eVTOLs.

In a comprehensive whitepaper jointly issued by EASA, FAA, Airbus, and Boeing in September 2022 aimed at “defining a blueprint for the modernization and harmonization of the aviation data communication landscape by 2035,” the regulators and aerospace manufacturers noted that controller-pilot communications are “currently supported by a set of technologies that rely to a large extent on VHF datalink and on first generation aviation SATCOM connectivity” that need to be upgraded.

“The technologies, standards and applications currently deployed for data communication in aviation … are fragmented and not systematically interoperable,” the whitepaper stated, noting “a high likelihood for saturation of the spectrum allocated to air-ground communications.”

But aviation data communication needs are expanding with the “always increasing information exchange needs in the airline operations domain,” the whitepaper stated, asserting that the “characteristics of the current aviation connectivity landscape (number of ‘connected’ aircraft, performance of existing links, lack of interoperability, etc.) are such that it is unlikely that future needs can be met without implementation of several significant, internationally coordinated changes.”

Direct data exchanges between commercial aircraft and controllers can have multiple benefits, Flohr said. “For example, downlinking the intended trajectory of the FMS enables ATC, much more often than is possible today, to provide fuel efficient separation through better accommodating the flight specific optimized climb and descend profiles,” he explained. “To close the loop, new datalink clearances will be uplinked to share the ATC intent … with the pilots for auto-load into the FMS after pilot acceptance.”

ANSPs Eye Trajectory Based Operations

This high level of data exchange will enable Trajectory Based Operations (TBO), which ANSPs, including the FAA, see as central to modernizing ATM. “Through improved strategic planning and management of traffic flows, TBO helps reduce reactive decision-making and use of static miles-in-trail restrictions,” according to the FAA.

NAV CANADA is “exploring game-changing flight data” processing that “will better integrate information from players in the aviation system to create a more consistent and predictive operation,” Cooper said. “Through Trajectory Based Operations, controllers and pilots … will have greater shared knowledge of their route, expected speed, and timings, reducing tactical intervention and extending the conflict detection horizon, while allowing us to adapt to changing weather and airport infrastructure availability more fluidly.”

But successfully implementing TBO “will require connectivity solutions that will bring significant capacity and performance enhancements over the ones currently deployed,” according to the EASA/FAA/Airbus/Boeing whitepaper. “Airline operations’ connectivity needs will continue to significantly increase, due to the continuous modernization of fleets and to the expected benefits of new data-centric … applications for optimization of operations.”

TBO enables controllers to use an “aggregate set of aircraft trajectories on the day-of-operation [to define] demand and inform traffic management actions,” the whitepaper stated.

TBO’s benefits are widespread, Flohr said, noting it “contributes to a CO2 emissions reduction through better support of flight specific-optimized descend and climb profiles.” He added: “A high capacity aircraft/ground datalink also enables the introduction of new Airline Operations Center (AOC) applications like regular airborne updates of weather, aeronautical information, and network management information … enabling the pilots to continuously keep the flight optimized in a changing environment.”

Indeed, SESAR believes airliners will need “multilink” capabilities that enable the aircraft to “switch seamlessly between different air-ground datalink technologies once they become available.”

The VHF Datalink Mode 2 (VDL-M2) currently used to support Controller Pilot Data Link Communications (CPDLC) is “performing poorly due to heavy congestion on the low bandwidth available,” Flohr said. “Very soon we will see the introduction of both a high bandwidth terrestrial datalink (LDACS) and a satellite-based datalink (SATCOM) for safety critical purposes, to complement and progressively replace the current VDL-M2 datalink … To go through the transition, it is important that airlines have the flexibility to choose which datalink technology to use, based on cost and performance considerations.”

With this “multilink vision” in mind, SESAR “is also researching the usage of public commercial datalinks,” such as via telecommunications providers, for aviation, “although this remains at a lower maturity level for time being,” Flohr said.

He added that airlines will need to deploy “technologies that can support multiple CNS functions simultaneously using the same spectrum,” explaining: “LDACS is a good example of what we call integrated-CNS technologies, which is primarily built and deployed to serve as a high bandwidth terrestrial datalink.”

Utilizing Satellite-Based Navigation Capabilities

Cooper noted that NAV CANADA has “gone through a significant shift towards satellite-based capabilities,” using space-based Automatic Dependent Surveillance “as a core surveillance source, providing coverage in areas where it has not been physically possible or fiscally reasonable to deploy radar.”

While oceanic airline operations rely heavily on satellite-based navigation, over-ground operations continue to be managed via a mix of space- and ground-based infrastructure. ANSPs increasingly are exploring using ground-based augmentation systems (GBAS) to allow aircraft equipped with a GPS antenna, a VHF antenna, and related processing technology to have a wider range of approach and landing options, increasing efficiency.

“NAV CANADA is paying close attention to this development, through platforms such as GBAS,” Cooper said. “While we are leveraging a number of satellite-based capabilities in both navigation and surveillance, our current combination of Performance Based Navigation capabilities and conventional ground-based navaids, such as ILS, serve our customers extremely well and help ensure resiliency of the system in a manner that matches prevalent aircraft systems.” He noted that the number of GBAS-equipped aircraft is “hovering around 5%,” making widespread implementation challenging at this time.

Even as global commercial air traffic returns to 2019 levels, with an expected acceleration beyond pre-pandemic levels in the near future, ANSPs have another factor to consider: incorporating advanced air mobility (AAM) aircraft into the airspace.

“The biggest challenge is in the CNS infrastructure for new entrants,” SESAR’s Flohr said. “The characteristics of drones and high-altitude [AAM] platforms are very different from the characteristics of commercial aviation, and hence they have different operational requirements that drive the need for CNS infrastructure. Added to that, the environments in which drones and high-altitude platforms operate are very different from the environment of commercial aviation.”

He emphasized this “does not imply that the multitude of drones [and AAM vehicles] will invade the airspace of commercial aviation,” explaining that “the first step in the [airspace] design is to start with segregated airspace.” But then there will have to be systems and rules in place to, for example, account for “a drone flying through ATC controlled airspace that will have to comply with normal IFR regulations and technologies.”