Surveillance avionics monitoring

Proactive and comprehensive monitoring of aircraft transponder performance.

Our surveillance avionics monitoring activities focus on the proactive, comprehensive monitoring of aircraft transponder performance by analysing data provided by ANSPs across Europe.

All mandatory surveillance capabilities (Mode S ELS - elementary, Mode S EHS - enhanced, ADS-B and ACAS), required by international, regional or national authorities are periodically checked or verified on an ad-hoc basis.

Our contribution

Investigating anomalies centrally is more efficient and leads to significant cost reduction for both air navigation service providers (ANSPs) and aircraft operators.

We use monitoring tools for installation at ANSPs’ sites to systematically process surveillance data and automatically detect initial signs of deficiencies - for example, the intermittent loss of detection, double detection, faulty Aircraft Identification or faulty transponder EHS content.

A unique laboratory test bed has been developed for this kind of investigation. It is capable of thoroughly testing all the capabilities and operations of any transponder. With this test bed, it is possible to investigate and resolve transponder anomalies, so avoiding expensive flight trials.

In the context of SUR Avionics Monitoring, EUROCONTROL maintains a regularly updated list of surveillance avionics design deficiencies and the Service Bulletins produced by manufacturers to correct them.

We cooperate closely with EASA to resolve avionics issues.


The main objective of surveillance avionics monitoring is to ensure that the airborne surveillance system infrastructure used in the European air traffic management (ATM) network functions properly and performs well in support of safe and efficient ATM operations including anti-collision systems (Aircraft Collision Avoidance System ACAS).

Undetected avionics problems can potentially affect safety, reduce the Network’s capacity, generate delays and degrade efficiency. The pro-active detection of avionics anomalies therefore helps improve the Network’s overall performance.

Issue management

If irregular behaviour is identified, the issue is investigated in more detail. When an aircraft does not comply with the regulation, the operators, manufacturers and regulatory authorities are contacted to resolve the issue.

Some problems are linked to standards that do not cover specific issues or are unclear, so the SCC Unit team actively participates in standardising Mode S and ADS-B in EUROCAE, RTCA and ICAO fora in order to make the systems safer and more efficient.

Any problem detected with Surveillance avionics - or when an air-ground interoperability issue is suspected - should be reported to the SUR Avionics Monitoring cell. We will then investigate the issue and, together with the stakeholders that need to be involved, take the necessary corrective action.

Working arrangements

The stakeholder group for this activity is the Surveillance Radio Frequency and Avionic Anomalies (SURFAR), which reports to the Surveillance Steering Group (SUR SG).