Article

The stakes are high as the aviation system evolves

12 May 2025

This covers

Skyway

Network performance

Communications, navigation and surveillance

Civil-military cooperation in aviation

Airspace design and utilisation

Jorge Pereira, Head of EUROCONTROL’s Communication, Navigation, Surveillance and Security Unit, Civil-Military Cooperation Division, highlights the importance of seamlessly accommodating and integrating military air operations in air traffic management digitalisation programmes.

The international aviation system is evolving to respond to the exponential growth in global mobility and to the resulting increase in air traffic levels, with aviation communications, navigation and surveillance (CNS) infrastructure undergoing a digital transformation.

In parallel, the aviation enabler infrastructure is increasingly impacted by performance disruptions and threats, ranging from the jamming and spoofing of satellite signals to cyber-attacks or the saturation of the aeronautical radio-frequency spectrum.

Military operations are impacted by such system vulnerabilities, which are amplified by the drastic connectivity and automation increase with a cumulative influence not only on (cyber) security and robustness/ resilience, but also on interoperability. In addition, the aviation infrastructure needs to address sustainability challenges to support the move towards greener aviation, to meet the specific requirements for new entrants – such as unmanned aerial operations – and new users of airspace, such as fifth-generation fighters, and also to explore emerging concepts related to high- altitude and space operations.

As the war rages in Ukraine, the European security and defence posture calls for stronger solutions and initiatives to address military aerial mobility requirements through arrangements to handle flights with mismatched aircraft equipage, and also to take advantage of the ongoing CNS digitalisation to deploy a true civil-military interoperable and robust CNS system capable of seamlessly accommodating and integrating military air operations.

Every year, the European aviation network processes hundreds of thousands of military flights operating under general air traffic (GAT) status. These flights rely on a communications, navigation and surveillance (CNS) infrastructure which is frequently owned/ operated by civil air traffic service providers.

Military (TACAN and UHF) infrastructure is scattered and insufficient in certain geographical areas (see Fig. 1 for TACAN), and military flights operating as operational air traffic (OAT) regularly require ATC services from civil air navigation service providers relying on the civil CNS infrastructure. Many of these flights are conducted by military aircraft that are not suitably equipped with the required systems for (civil) ATM/CNS capabilities.

Figure 1 - ECAC TACAN Conventional Redundancy FL150 (civil AIPs)

In such cases, compliance with the applicable ATM/ CNS requirements or alternative accommodation solutions (e.g. exemptions/derogations) are an absolute imperative. Compliance or accommodation can be achieved in multiple ways as decided by the national regulatory authorities. Arrangements to handle non-equipped military (or State aircraft) flights must remain in place. An example of other options is to take advantage of performance-based technical solutions, enabling the reutilisation of available military capabilities, hence reducing integration and technical constraints. Such military capabilities are usually jam- resistant and more robust against RF interference or other disruptive attacks, offering additional security benefits.

Spectrum efficiency, security and robustness/ resilience challenges, the use of common technical standards and procurement synchronisation are some of the transversal aspects to consider when future infrastructure solutions are delineated.

As a result of digitalisation and an intensive data- sharing environment, it becomes vital to guarantee a mechanism to permanently monitor the level of CNS performance, continuity and availability of the underlying CNS infrastructure at Network level. Such tasks are presently performed by the EUROCONTROL Network Manager.

CNS evolution is not only about the introduction of new cutting-edge technological solutions, but also the removal of an excess of certain infrastructure segments. When CNS overprovision is to be tackled and the CNS aviation infrastructure starts to be rationalised/ optimised, a number of principles must be observed, including the recognition of national responsibilities, the retention of minimum operational networks (MONs) and mandatory civil-military coordination prior to the planning stages.

Many States operate CNS infrastructures configured in accordance with local and specific air traffic service and military command and control organisations. Fragmented service provision and infrastructure configuration is a reality across Europe. This causes interoperability gaps and mismatches that call for transnational harmonisation efforts to be made in the context of ATM/CNS deployment planning.

The recent regulatory developments in the European Union (e.g. recast of interoperability regulations and the new conformity assessment framework) place a new emphasis on the national regulatory context and call for further harmonisation initiatives to ensure homogeneous levels of cross-border air traffic service provision and infrastructure support. Such harmonisation efforts must be based on national plans and infrastructure configurations.

In addition, these harmonisation efforts must consider military requirements during the deployment of new technology improvements leading to the implementation of a common-use civil-military CNS infrastructure. The need for special handling must be minimised.

The ATM Master Plan and the future CNS Evolution Plan are key references to ensure wider coherence and CNS interoperability and resilience across Europe. The CNS Evolution Plan is to be developed by the newly established CNS Programme Manager who maintains a very good level of consultation with the national military authorities. Adding a military dimension to these documents is of utmost importance in order to ensure that the resulting infrastructure can seamlessly accommodate military operations at the appropriate level of interoperability, performance and security/ resilience.

"Operational/cost benefits will be the basis for military adherence to new concepts and a new technology environment."

The determination of military requirements (interoperability, safety, spectrum efficiency, security, etc.) that need to be reflected in CNS PM deliverables, is an ongoing activity building upon excellent coordination levels maintained between national military authorities, EUROCONTROL, the European Defence Agency (EDA) and NATO.

Operational/cost benefits will be the basis for military adherence to new concepts and a new technology environment. In addition, investments in solutions for compliance are to be incentivised on the basis of financial instruments, including those offered by the European Commission with regard to military mobility and Connecting Europe Facility (CEF) programmes managed through the SESAR Deployment Manager (SDM), with military involvement facilitated by the European Defence Agency (EDA), together with technical support from EUROCONTROL.

The evolution of the CNS infrastructure (Fig. 2), the need to progressively ensure its civil-military relevance, and the related civil CNS deployment initiatives have given rise to a number of civil-military interoperability challenges, which are examined below.

A future common-use infrastructure (Fig. 3) must rely on secure data-sharing based on Internet Protocol (IP) technologies, standardised SWIM services, data models and technical infrastructure profiles. Military access to such a network-centric environment is essential. However, security measures to safeguard military-sensitive information and interfacing will be paramount, too.

Air-ground interoperability will be a fundamental challenge to enable trajectory management and other advanced operational concepts. This means that, in some cases, military operators are considering the use of civil datalink services (ATN/VDL-2 followed by FCI) for controller-pilot datalink communications applications and, subsequently, for ADS-C/EPP services to support the exchange of 4D trajectory data in real time. This is more relevant as a voluntary option for transport-type State aircraft flying regularly above flight level 285.

Figure 2 – CNS Technology Evolution

Figure 3 - Common-Use Infrastructure

The move from conventional to multi-tracking area navigation (RNAV) based on ICAO’s PBN (Performance Based Navigation) concept, including the optimisation of air traffic service routes and instrument approach procedures, is a development that significantly impacts military operations.

A sufficient level of conventional means of navigation must remain in service to handle non-PBN-equipped State aircraft in line with national transition plans. In parallel with equipage exemptions, performance- based solutions will be essential for State aircraft compliance with PBN, maximising the reutilisation of military airborne capabilities (e.g. military inertials, GPS-PPS/GNSS restricted signals, TACAN, differential GPS, and enhanced visual systems).

Alternative positioning, navigation and timing (A-PNT) solutions should ideally consider TACAN (as part of a multitracking solution to be defined) as a means of navigation equivalent to DME/DME.

Military flights conducted in a mixed environment must be integrated into the surveillance chain, as they provide updated information on aircraft identification, position and other aircraft-derived parameters for safe separation in a defined volume of airspace.

The (civil) terminal and en-route surveillance infrastructure is evolving towards an optimal mix of surveillance systems, including SSR Mode S, wide area multilateration (WAM), and automatic dependent surveillance– broadcast (ADS-B) systems. In parallel, a layer of independent and non-cooperative surveillance (primary radar) systems will remain available for all flight phases in order to track non-transponding targets.

To conceal military information and prevent the disclosure of SUR data and flight identification data via public internet platforms, many military operators have decided to use Mode 3/A C only (Fig. 4). In addition, spoofing and similar threats represent a significant risk for ADS-B. Consequently, security solutions enabling the military to use surveillance infrastructure are urgently needed.

Figure 4 - Reversion to 3/A Operations

The performance of the CNS European infrastructure is being monitored on an ongoing basis, and this is organised in the context of the regulated network functions covering datalink services, altimetry, collision avoidance, GNSS and 1030/1090 MHz provision. CNS monitoring requires a significant level of civil-military coordination.

The Network Manager’s activities in the area of CNS performance monitoring entail close coordination with military operators to address cases of radio frequency interference, 1030/1090 MHz over- interrogation, GNSS outages, jamming and spoofing, transponder anomalies, altimetry errors exceeding limits and datalink provision with technical failures.

In fact, CNS monitoring results might impact State aircraft operating as GAT and might impact military infrastructure when subjected to radio frequency interference or over-interrogation. Significant civil- military coordination efforts have been facilitated by EUROCONTROL and the Network Manager to identify occurrences involving direct contact with national authorities to determine the origin of GNSS interferences and to resolve some 1030/1090 MHz over-interrogation events and transponder anomalies.

Strong civil-military coordination is also key to address 1030/1090 MHz RF pollution and over-interrogation in order to maintain safety levels and minimise impacts. In some cases, navy assets (shipborne radars) are also used.

The need for higher levels of infrastructure resilience/ robustness must be translated from buzzwords to concrete mitigating measures stemming from validated research solutions to industrialisation and deployment initiatives. A proper definition must consider the known threats (e.g. GNSS jamming and spoofing) (Fig. 5) and mitigation measures, including redundancy. It should incorporate a layered approach and assess resilience levels, considering civil systems and cross-border dimensions. Specific security and defence resilience criteria shall be considered in the elaboration of the acceptable level of service continuity for CNS infrastructure segments ranging from datalink security to ADS-B anti-spoofing/authentication or RF interference mitigation mechanisms.

Figure 5 - GNSS Jamming and Spoofing

The CNS infrastructure of the future must have a common-use civil-military nature in order to fulfil the specific requirements for various airspace users. Performance-based CNS concepts (Fig. 6) are fundamental for the military in order to achieve interoperability and compliance without prohibitive costs and cumbersome equipment retrofits.

More attention needs to be paid to security, robustness and resilience, which must be adequately addressed (including through industrial research) in order to resolve infrastructure vulnerabilities associated with automation and connectivity and to allow for the exchange of information between civil and military entities.

However, interoperability efforts should never overlook the need to maintain transitional accommodation arrangements for handling non-equipped aircraft.

CNS provision must be aligned with sustainability objectives through improved flight efficiency. New entrants and spectrum efficiency and compatibility are other aspects requiring strong civil-military coordination.