Finding Commonality in Air-Ground Data Communication Strategies

A joint effort between the U.S. and the European Union identifies criteria in transitions toward achieving airspace harmonization.

Data communications has been introduced domestically in both the U.S. and EU. Due to differing requirements and operational needs and the availability of different data communications technologies with existing fleets and aircraft offerings, different initial technical paths were chosen by each region. As implementation programs successfully progress past initial stages, operational concepts and technical provisions continue to evolve, and operational capabilities beyond the current implementations are required. In order to avoid divergence beyond initial individual data communication programs, the U.S. and EU data communication programs established a set of convergence objectives. As the programs continue toward more advanced operations, a strategic path toward those convergence objectives needed to be established.

The U.S. and EU have developed an air-ground data communications strategy under the auspices of the U.S.-EU memorandum of cooperation, a joint venture whose objective is to help address research and development-related issues to support technology implementations. Steve Bradford, chief scientist for the FAA’s NextGen Program, and Michael Standar, chief strategies and external relations at the SESAR Joint Undertaking, have overall responsibility for the system-level integration of the more than 25 action plans currently in the works under the venture, including the strategy document. The aim of the strategy document is to objectively describe the short-, medium- and long-term ongoing activities and plans of the U.S. and the EU and to operationally and technically address the common challenges and opportunities that exist to achieve interoperability and harmonization.

The key objective of the developed strategy is to guide and drive the future investment plans of the government and the industry in the U.S. and Europe as well as worldwide and to facilitate convergence to common equipment and minimize unnecessary divergences and investment risks. This joint effort involved multiple stakeholders from the government, regulators, Standards Management Organization (SMO), and the service and manufacturing industry. As such, it captures the known needs and requirements of airspace users. The actions and activities this strategy identifies will need to be further worked together with the airspace-user community. The aim is to move the necessary elements of the strategy and the results of the actions into the International Civil Aviation Organization’s (ICAO) Global Air Navigation Plan/Aviation System Block Upgrade (ASBU) framework in order to ensure globally harmonized use of air-ground data communications in ATM operations.

The strategy document focuses on three principle elements around which harmonization needs to be achieved: data communications ATM service applications, communication network(s) over which the applications are running, and physical link(s) over which the applications’ data are transmitted and the networks interface.

From this, a consolidated U.S./EU air-ground data communications roadmap was developed. The roadmap represents the short-, medium- and long-term on-oing and planned developments and implementations in the U.S. and in the EU. The roadmap also includes a view for oceanic operations.

Consolidated U.S. and Europe air-ground data communications roadmap.

The comparison of this roadmap for ATM operations in their respective continental and oceanic airspaces points to a target-harmonized environment based on ATN/IPS for the network, Baseline 2 (B2) for the ATM operational service applications, and a mix of current VDL Mode 2, new high-bandwidth satcom, a new terrestrial physical data link and other means suitable for ATM operational services.

For the area of applications, there is agreement that B2 is the convergence target to achieve harmonization.

An ACARS network has been deployed in the U.S. to support the use of FANS 1/A applications in the short-term. In the mid-term (pending the outcome of further benefits studies), the U.S. plans to introduce an ATN/IPS network to support FANS 1/A, B2revB, and future applications.

Europe has deployed an ATN/OSI network to support the use of B1 applications in the short term and plans to leverage this infrastructure to support B2 applications in the midterm. In the long term, Europe plans to deploy an ATN/IPS network and for the longer future intends to support the evolution of B2 to more advanced B3 applications.

Evolution to target harmonized environment.

For the area of physical links, the U.S. and EU will start with their existing VDLM2-based networks. While both the U.S. and the EU agree that a new high-bandwidth SATCOM capability is probably required in the longer term, the use of existing and emerging high-bandwidth satcom may also be used in the short and medium terms to supplement existing capabilities and help transition to the long term. There is also a need for a new supplemental broadband terrestrial link capability in the long term, although the exact nature of the operational usage of this link is still under development. Because standards development is a time-consuming process, it has been recommended that efforts begin in AEEC, RTCA and ICAO to develop standards for these future technologies.

Transitioning to a Harmonized State

It is important to facilitate the transition to the harmonized end state, taking into account the different starting points, legacy infrastructure, investments needed for the industrial developments, equipage and implementation schedules, as well as the accommodation of aircraft operating in different regions.

Given the current regulatory environment in the U.S. and Europe, airspace users are asked to comply with different equipage requirements. Considering the general commonalities in the current and target environments for the application and physical links, it is the network element (moving from ACARS in the U.S. and ATN/OSI in Europe to ATN/IPS) that poses more challenges for the transition. It should also be noted that moving toward B2 applications, in particular from a B1 environment (which is not TBO-based), presents significant operational, technical and temporal differences.

As there will be different user equipage in different regions, there is a need for coexistence and simultaneous operation for potentially all three network technologies. It is expected that as ATN/IPS becomes more prevalent, ATN/OSI and ACARS usage will start to decline.

Applications for ATS data communications implementations in SESAR and NextGen.

The objective is therefore to harmonize transition paths to reach the desired convergence state, taking into account different starting points and legacy infrastructure, different requirements for local implementation of data communication services, accommodation of long-range aircraft flying in multiple environments, and the economic impact of dual equipage and associated industrial developments.

Transition Scenarios

An important aspect of harmonization is not just the identification of and agreement to an end state, but also how to transition from current generation applications, networks and physical links to future ones. “Big bang” approaches do not tend to work well in aviation, especially when there are large numbers of equipped aircraft and ground systems that will need to change in short order. Changing equipage on aircraft is expensive and time consuming. Additionally, it is difficult to support multiple different technologies in different airspaces. Given these realities of dealing with existing and emerging technology, making maximum use of existing equipage is a viable way forward and has many benefits.

The strategy document identifies two different transition scenarios for further consideration and analysis. One is to wait until operational benefits promote regional transition. The other is to use equipment gateways to support interoperability between diverging implementations and to facilitate transition to the harmonized end state.

Under the first scenario, the plan would be to move from the current environment to an agreed-upon harmonized environment as justified by operational benefits and equipage advantages. Making extended use of current equipage allows the airlines and ANSPs to gain additional usage of their existing equipage, thus putting off the large investments required to move to the newer technologies. This may diminish the benefits of the early adopters and bring us back to a last adopter advantage, which has been determined less attractive by the user community in ICAO. However, this negative aspect could be offset by the continued experience and benefits gained with the existing technology, applying lessons learned to defining new B2-enabled services.

Conceptual gateway operation.

Additionally, there needs to be a better understanding of the benefits that will result from new equipage, as well as when sufficient numbers of aircraft with new equipage will be available. The delta in benefits between using B2 services and the existing services should also be defined in order to support the overall business case.

The second scenario introduces the potential of gateways for facilitating early interoperability between interim diverging implementations. While there was some discussion on airborne gateways for specific physical links (like satcom), a gateway on the ground may be more realistic to support multiple technologies in the most economic, efficient way.

As previously mentioned, changing equipage on existing aircraft is expensive, and the use of forward-fit only is time consuming. Therefore, an approach is needed that would allow the initial introduction of ATN/IPS while preserving backward compatibility for other equipped aircraft, ensuring that airline and ANSP investments are preserved as much as possible while providing a transition path to the envisaged end state.

As discussed in various forums, such as AEEC, there will likely not be a triple stack in the aircraft. Therefore, much of the accommodation would have to be done on the ground. This would include potentially both FANS-1/A and B1/B2 applications, meaning there would need to be ACARS to ATN/IPS and ATN/OSI to ATN/IPS translation capabilities (and vice versa).

At a conceptual level, a gateway might work for ATN/IPS, ACARS and ATN/OSI accommodation. Aircraft can fly as equipped and communicate with the gateway over their preferred protocol. The communication between the gateway and the aircraft and the gateway and the ground system would be done via supported ground protocols. Application-level data is not affected, which is advantageous. This also means that the gateway would not need to have additional mechanisms to solve application differences (e.g. between FANS-1/A and B2 as per DO-352A ).

A more detailed planned study would allow for a more accurate recommendation going forward. AVS

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