CPDLC Coming of Age

CPDLC Coming of Age

Data communications between pilots and air traffic controllers are designed to replace routine voice exchanges and to link an air traffic control agency’s ground automation systems with flight deck avionics to support ATC clearances, instructions, traffic flow management inputs, and flight crew requests. However, as Aimée Turner reports, significant infrastructure issues still need to be resolved if European Controller Pilot Data Link Communications (CPDLC) are ever to fulfill their potential.

Controllers are increasingly able to deliver instructions with a click of a mouse, without the need to use voice frequencies, an advance that is paving the way for an aircraft’s flight management system to receive the complex digital instructions necessary to make trajectory-based operations a reality.

Europe’s data link mandate was first fielded back in 2009, with an applicability date of 2013. But equipage rates both on ground and in the air did not develop as expected, hampered by serious technical issues that severely reduced the availability of data link for ATC use, initially delaying the mandate by five years.

Those initial CPDLC failures led the European Union in 2016 to appoint the SESAR deployment manager to resolve the issues and relaunch the program. It has since managed to help turn around the situation, reporting significant progress in efforts to boost the airline and ground equipage baseline necessary to allow the future vision of a system-wide digital exchange of information between aircraft and ground. Today, it reports that 80% of eligible aircraft are now equipped with the requisite CPDLC avionics, twice as many as in 2018.

One of the technical challenges that continues to weigh on the industry has been the ICAO ATN protocol creating too much overhead for the capacity of the VHF Digital Link Mode 2 (VDL-M2) system, which is used to support data link between aircraft and ground stations. The technology supports Airline Operational Control (AOC) as well as Air Traffic Services (ATS), and the industry believes that it is not a question of if, but when this will become congested and therefore potentially performance-limited, when air traffic volume picks up pace again.

Complex infrastructure issues still need to be resolved if European Controller Pilot Data Link Communications (CPDLC) are ever to fulfill their potential.
Complex infrastructure issues still need to be resolved if European Controller Pilot Data Link Communications (CPDLC) are ever to fulfill their potential.

Complementary technologies, including the terrestrial LDACS (L-band Digital Aeronautical Communications System) are being developed, which support data link but are also expected to evolve to support navigation functions and voice communication in the future. Iris satcom is already being tested as a data link-compliant satellite system.

The LDACS system is a valid candidate for the ATC community to use as a replacement for VDL, but it will take several more years for the SESAR Joint Undertaking to prove it capable of replacing VDL and for avionics vendors to develop certified LDACS radios. LDACS is certainly not as advanced as the Inmarsat Iris system, which is already being flight tested and will likely be the first alternative to VDL to be used operationally for CPDLC. (See Inmarsat Flight Trials page 30.)

Europe Develops Future Perspectives on Air/Ground Data Communications

air ground data

The evolution of the air traffic control air/ground data link is inextricably linked to the SESAR vision to bring trajectory-based operations to Europe, according to SESAR 3 Joint Undertaking experts Olivia Nunez and Ruben Flohr, who outlined the status of research on air-ground data communications for Aerospace Tech Review.

By continuously and collaboratively (pilot and ATC) optimizing the 4D-trajectory of a flight against evolving operating circumstances, like weather and traffic, the flight always remains as close as realistically possible to the airline’s requested flight trajectory.

SESAR 3 JU research is focused on the execution phase; the high traffic density of the European airspace, with its many short hauls (less than 2-3 hours), justifies this, as its complexity requires intensive ATC decision-support to keep all trajectories optimized.

“Our solution work aims to build on a reliable bidirectional data connection between flight deck and the ATC systems, the so-called Aeronautical Telecommunications Network-Baseline 2, consisting of the downlink of the flight management system predicted trajectory, called the extended projected profile, and a clearance uplink, via controller-pilot data link communication,” said Flohr.

When the autopilot follows the FMS plan, the EPP describes the optimum trajectory within the constraints known, allowing ATC to accommodate the aircraft’s performance when resolving conflicts or building sequences. This will reduce the need for inefficient early descents, for example.

Regarding CPDLC, the SESAR 3 JU, with its members and partners, is working on new clearances for uplink and auto-load, after pilot acceptance. The first is the enhanced vertical clearance. By knowing the EPP, a vertical clearance is composed to avoid intermediate level-offs, improving the efficiency of vertical profiles. The second is the 2D trajectory revision, substituting two sequential instructions of vectoring (conflict resolution) and resume own navigation. The composite clearance improves the predictability for ATC, pilot and FMS, allowing immediate re-optimization.

“As outlined in the European ATM Master Plan,” said Nunez, “the future data link will be based on the ATN internet protocol suite and will include a multilink switch between terrestrial (LDACS), satellite (satcom) and airport surface data link (AeroMACS). This is expected to improve bandwidth, latency, reliability, prioritization mechanisms and security. It also supports the rapid increase of airline-crew data traffic that is currently impacting ATN-B2 exchanges.”

For a smooth transition to the future environment, there will be ground proxies translating between the different protocols (FANS, OSI, IPS). The ATN-B2 standard (EUROCAE ED-228 / RTCA DO-350) will be updated to incorporate validation results from the following projects: DIGITS – P.J.31 now completed; ADSCENSIO PJ.38, end-date June 2023; and 4DSKYWAYS – PJ.18, end-date 2023.

ATM industry body CANSO supports the view that each of these technologies, LDACS and satellite communications systems, offers some unique benefits and technical capabilities which complement each other. Satellite systems are especially well-suited for large coverage areas with less dense air traffic, like oceanic remote and upper continental airspace regions, while LDACS is well-suited for dense air traffic areas, such as lower-level continental areas or hot spots around airports and terminal airspace. Together, they are expected to constitute the pillars of a data link multilink concept, although CANSO says this approach of integrating complementary technologies risks failing due to no organization actually “owning” the project.

CANSO therefore believes that the establishment of a common European Datalink Service Provider could prove critical in harmonizing data link provision and governance in Europe. A future DSP is, it insists, the prerequisite to ensure that the required service performance will be systematically met, while at the same time allowing for multiple commercial actors in data link service provision to be seamlessly integrated and charged. Indeed, one additional benefit of the DSP is how it will change the way that DLS is charged across Europe, with a User Pays Principle to be adopted, where each air navigation service provider pays for the service in accordance with its usage, rather than the more arbitrary and fragmented set of rates which is currently employed

Moves are underway to establish such a common provider entity, initially through an initiative known as the ATS Common Datalink Services governance for Europe or ACDLS, with a funded project called CoDE to develop parts of this. Launched in October 2021 by the A6 Alliance — a consortium of ANSPs driving ATM modernization — and Eurocontrol, with the support of the SESAR Deployment Manager, the ACDLS aims to pave the way and accelerate as much as possible the establishment of a Common European Data Link governance within the SES Digital Backbone framework. The agreed schedule foresees the selection of the future DSP by the third quarter of 2022, its establishment in early 2023, and an operational start date of 2025 — earlier if possible.

Establishment of a common European Datalink Service Provider could prove critical in harmonizing data link provision and governance in Europe, according to CANSO.
Establishment of a common European Datalink Service Provider could prove critical in harmonizing data link provision and governance in Europe, according to CANSO.

This European plan seems to mirror the U.S. FAA’s $331 million ATC data link service contract with Harris Corp. in 2012, which required Harris to subcontract with SITA and Collins to use their VHF networks. What is being envisaged is that the European ANSPs will contract with this future single DSP to secure the service they need for CPDLC, and that this single DSP will also contract with SITA and Collins to use the VHF networks they use to provide the airline data link service, as well as all other networks and technologies.

An industry insider told Aerospace Tech Review that the FAA’s expected model was preserved in the Harris subcontract with Collins/ARINC, who retained ownership of their stations, but that the Harris SITA model was different. The Harris-SITA contract provided Harris with SITA’s U.S. VHF ground stations — which used Harris computers — and an ACARS service processor, giving Harris a VHF ACARS network to provide the FAA service. The deal allowed SITA to use the Harris-owned network to provide the service it sold to airlines.

SITA had already done the same in Europe, selling VHF ground stations to many of the ANSPs — including principally DFS in Germany, Spain’s AENA and France’s DSNA — except that they used ATN routers, not a ACARS processor. The SITA deals struck with the European ANSPs also allowed SITA to use the VHF stations to provide airline ACARS service, with the ANSPs contracting in parallel with Collins/ARINC to get data link access to their customer aircraft.

ARINC also sold VHF stations to a few European ANSPs, although far fewer than SITA. Some European ANSPs did not buy stations from either SITA or Collins/ARINC and instead established VHF service contracts with both.

“The problem with all these arrangements in the first generation of European CPDLC implementation,” said the insider, “was that the ANSPs did not create any central organization to ensure the service worked. And when they all turned on CPDLC, they collapsed the VDL network.” It is expected that a future DSP will not change the ownership model of the underlying air-ground technologies, but will serve to harmonize the procurement and provision of the services under one agent for ANSP use.

U. S. Data Comm Program Builds on Early Success

The FAA and European aviation authorities both deliver regular updates on the deployment status of CDPLC. At one of the recent ARINC Data Link Users Forums, the FAA reported that since 2016, its air traffic controllers had cleared more than 10.6 million flights using CPDLC through its Data Comm program, saving 2.73 million minutes of radio time and nearly 2 million minutes of airspace user time, which not only prevented 140,870 readback errors but also saved 22.44 million kilograms of CO2 emissions.

Outlining Data Comm tower benefits between June 2016 and July 2021 last September, Jesse Wijntjes of the FAA and Chris Collings from L3Harris reported that key area control centers in Kansas and Indiana had been fully operational since November 2019, with the Washington control center launching 24/7 operations in March 2020.

They told the forum that although all Data Comm activities for the remaining facilities had been paused due to COVID-19, the U.S. aviation agency was continuing to work on avionics and air-to-ground interoperability and apply the lessons it had already learned to help reduce deployment risk for its remaining 17 area control centers. Indeed, the agency restarted planning and deployment activities in April 2021, although a resurgence in COVID-19 cases has impacted the resumption of deployment activities.

Paul Prisaznuk is head of standards development at ARINC, leading efforts to establish consensus in aviation technical standards. “The main takeaway in the CPDLC community from the most recent updates is the growth and success of CPDLC at major airports throughout the world,” he said, pointing to the communication times saved compared with voice, in addition to reduced delay times in and around airports.

“The outcome of that VDL collapse was that the ATC community designated the SESAR Deployment Manager to technically integrate and harmonize the service provided by the combination of the VHF network elements,” he said. “Now they are creating the single DSP to operate the data link service required by the ANSPs, using the combination of the VHF network elements.” He pointed out that the European ANSPs owning VHF ground stations means the European single DSP will use some stations owned by the ANSPs, so there will likely be a complicated combination of contracts.

The European ANSPs, together with Eurocontrol, established the governance for the ATS Common Data Link Services in October 2021, and its organizational structure provides the mechanisms necessary to procure and select a DSP and also to manage its obligations in service. The governance side is organized in two distinct levels: an executive level, which envisages the presence of the Top Management Body and the DLS Governance Executive Board, with a management level to oversee the DSP as a DMU. The executive and management bodies are responsible for the DLS strategy management, the DLS governance management, and DSP contract compliance monitoring, as well as liaising with users, airspace users and the regulator.

One candidate that could become the common DSP is understood to be the ESSP organization, which is also working with Inmarsat on the British satellite business’s Iris satellite data link program. Toulouse, France-based ESSP styles itself as an “experienced and dynamic company specialized in the operations and provision of satellite-based services to aviation” — providing EGNOS, the satellite-based augmentation system for precise satellite positioning — and already holds a pan-European certification to deliver ATC-grade CNS services. Other organizations will also be in the running for the DSP and some are likely to give ESSP a run for its money.

Eurocontrol will manage the procurement and assessment process in order to select a Datalink Service Provider and it may want its governance to extend over the new data link service provider. Busy terminal at Heathrow shown above.
Eurocontrol will manage the procurement and assessment process in order to select a Datalink Service Provider and it may want its governance to extend over the new data link service provider. Busy terminal at Heathrow shown above.

Eurocontrol will manage the procurement and assessment process in order to select a DSP, as it did for NewPENS, and although ineligible to become wholly or part of a DSP itself, it may well want its governance to extend over the new data link service provider. In fact, one of the aims of the ACDLS, under the SES Digital Backbone initiative, is common governance. The fact that DLS and NewPENS are both key pillars of the SES Backbone could mean significant convergence in terms of governance at the top level.

Inmarsat Flight Trials Recent Flight Trials are Demonstrating that Satcom Has the Capability to Sit Alongside VHF in a Multi-link Capability (with PIC)

Significant progress is being made in Europe through Inmarsat’s Iris project, which is seeking to establish a long-term replacement for VDL. Aerospace Tech Review spoke to Danny Bharj, director of technology programs at Inmarsat Aviation, about the results of the latest flight tests of a modified Alaska Airlines 737-9 being operated by Boeing for its 2021 ecoDemonstrator. Inmarsat is using this to evaluate the use of IPS-based satellite data link communications between pilots and controllers to ensure it can be securely executed.

ATR: How have the flight tests performed?

DB: It’s tremendously exciting to be a part of the Boeing ecoDemonstrator program, which accelerates innovation by taking promising technologies out of the lab and testing them in the air to solve real-world challenges for airlines, passengers, and the environment. As part of the program, Boeing has tested the important new ATN/IPS (Aeronautical Telecommunication Network using Internet Protocol Suite) components for our groundbreaking Iris air traffic modernization solution. It has performed flawlessly during the in-flight evaluation stages. The full results are in the process of being validated by Boeing and are currently not public.

Powered by our ELERA global satellite network, Iris enables real-time collaboration between pilots, air traffic controllers and an airline’s operation center, using cost-effective, secure and highly resilient data link communications. As a result, they can calculate the shortest available routes, determine flight trajectories and cruise at optimum altitudes, while also receiving the latest digital information, such as weather updates. This not only improves airspace usage to accommodate future growth, but also allows airlines to minimize delays, save fuel and reduce the environmental impact of their operations.

ATN/IPS is currently being finalized as the global standard for air traffic control communications to and from the aircraft. And this is the first time it’s been trialed on flights, marking an important step forward in Iris’ global rollout and unlocking significant benefits in service scalability, bandwidth, and throughput for Air Navigation Service Providers and airspace users.

ATR: Boeing selected the Iris solution for testing, as it is closely aligned to its own commitment to reduce the environmental impact of modern aircraft. Can you outline the ways in which IPS-based satellite CPDLC achieves those objectives

DB: Boeing selected Inmarsat for this program in order to evaluate how satellite communications (not just ATN/IPS specifically) can contribute to reducing the environmental impact of aviation. ATN/IPS provides the same benefits as ATN/OSI, with the biggest contribution to sustainable aviation coming from 4D trajectory-based operations and constant descent profiles, which enable more capacity in the airspace and less fuel burn.

In addition to ATN improvement, satellite communications also contribute by providing secure and resilient cockpit connectivity for real-time EFB applications, such as live weather forecasts and satellite-based observation data to create more economical flight plans and adjust them on the go. By evaluating fueling decisions using real-time weather intelligence from en-route aircraft, airlines can also calculate the right amount of fuel to carry, thus reducing the additional fuel burn from carrying superfluous fuel.

Alaska ecoDemonstrator

ATR: How far have the trials demonstrated that satcom has the capability, both from a latency and a capacity point of view, to be able to sit alongside VHF in a multilink capability?

DB: When you analyze the performance of Inmarsat Iris, which uses our SwiftBroadband-Safety (SB-S) platform, it’s on a par with VDL in every aspect except one: We have significantly higher bandwidth of 200kbps versus the 31.5kbps provided by VDL, and more capacity. It’s widely accepted that VDL is nearing capacity in several regions around the world, and that moving to satcom (such as the Iris program in Europe) is a solution to that challenge. Additionally, Inmarsat SwiftBroadband has been proven through decades of use as part of FANS1/A, and our latest service, SB-S, is used by over 215 aircraft in regions across the globe and is meeting or exceeding the required performance for a number of operational uses, including the Four-Minute Mandate in China.

ATR: Have there been any operational issues, considering these trials were the first outside of European airspace?

DB: No operational issues have been experienced during the trials of ATN/IPS. We take our role in aviation safety extremely seriously and have extensively tested the solution not just in our own aviation lab in London, but also in testing with Boeing labs in Seattle prior to it taking flight.

ATR: How has end-to-end Internet Protocol version 6 (IPv6) operation — the flight management system and communications management unit through satcom — performed?

DB: Our performance was shown to meet the aviation data link requirements for Europe. We are moving to use the IPv6 standards as defined by SARPS, RTCA, EUROCAE, ICAO and AEEC, which are being written in such a way as to ensure performance is not affected compared to IPv4. The software required for IPS functionality was built specifically for this program, but what issues and small areas may still need to be validated? We may need to update elements as the industry standards activities progress. This functionality was developed on current industry standards and as the new standards are produced, there may be some amendments required.

ATR: How do the results of the demonstration impact on what Iris will be able to perform when it enters into service next year?

DB: Iris will use ATN/OSI operationally next year. ATN/IPS will not be available operationally for a few years yet. Boeing will use ATN/IPS, and the Iris infrastructure will have the capability to support ATN/IPS flight trials in 2023.