Inside GNSS Media & Research

SEP-OCT 2018

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Page 54 of 67 S E P T E M B E R / O C T O B E R 2 0 1 8 Inside GNSS 55 bility Study, Additional Resources) to support seamless GNSS operations has been abandoned. Given that GNSS is not avi- ation-specific, but a shared system not under direct aviation control, ICAO and its member States recognize that alternative CNS capabilities will remain necessary. e 12th Air Naviga- tion Conference tasked ICAO to investigate the "need for and feasibility of " an Alternate Positioning, Navigation and Tim- ing (A-PNT) system (Additional Resources). e preliminary conclusion is that while GNSS is evolving from a supplemental means to a primary means, the terrestrial navigation aids (ILS, VOR, DME) will evolve from their conventional, primary role to what some call a "Minimum Operational Network" to help ensure safety and continuity of operation in cases of GNSS out- ages. EUROCONTROL has been actively engaged in the develop- ment of mitigations against GNSS vulnerabilities, with the aim to make aviation use of GNSS as robust as possible while find- ing the right balance for retaining conventional capabilities. ICAO included the resulting "GNSS RFI Mitigation Plan" in its GNSS Manual, ICAO Document 9849, 2017 edition. A measure implemented at the European regional level is the inclusion of GPS Outage Reports by pilots in the EVAIR database ( Figures 1 and 2 ). EVAIR stands for EUROCONTROL Voluntary ATM Incident Reporting, where GNSS issues are one among many others. Pilots flying GPS-equipped aircra over a decade ago were generally not concerned by GPS outages, since they believed "GPS always works". is is a tribute to the continued quality of service provided to aviation. e three main GNSS vulnerabili- ties which can cause service outages are constellation weakness, propagation anomalies due to solar activity (ionosphere) and radio frequency interference (RFI). GPS constellation perfor- mance has been very good over many years and solar activity has not been dramatic, which leaves RFI as the main vulner- ability. One problem with RFI outages was that they were not seen – because aviation did not look for them. Now that avia- tion is making a more conscious effort to collect pilot reports, we see that GNSS outages due to RFI occur on a still rare, but nonetheless regular basis. Normally, they constitute nothing more than an operational nuisance due to the redundant CNS capabilities on board aircra and on ground. A lot more could be said on normal interference mitigation, including uninten- tional interference, intentional interference not directed at avia- tion and intentional RFI directed at aviation. However, this is not the focus of this article. Depending on the definition used, spoofing can be seen as either a special form of radio frequency interference, or as a completely separate category. Recently, the lines between spoofing and jamming have started to blur, as there can also be spoofing for denial of service, where a receiver locks up due to anomalous data – there is no RF overload but the result for receiver operation is still more or less the same. Spoofing Mitigation and the CNS Security Context e civil aviation position on GNSS spoofing some years ago was simple: it is not our problem. Spoofing was considered an advanced military capability, and therefore outside of the scope of civil aviation. If it would happen, the military would be called in to manage the situation and the affected airspace would be closed. Similar to the evolution of normal RFI to an actively managed topic, the view on spoofing is also chang- ing. Triggered in part by the Hannover GNSS repeater incident (Naerlich, Additional Resources) it is now recognized that a variety of in-between spoofing stages exist, starting at badly adjusted repeaters and evolving to whatev- er any reasonably skilled, unreasonable tin- kerer can obtain legally and cobble together with a modest investment. It is important to recognize that cur- rently, aviation is not shamelessly exposed to spoofing without any defense. While some may complain about the diverse outdated and spectrum-inefficient multi- tude of CNS systems used by aviation, this redundancy is essential to detect when there are unusual outputs from the GNSS sensor and to be able to continue the opera- tion to a safe landing. Pilots are trained to detect and deal with equipment malfunc- tion in every phase of flight. However, one FIGURE 1 Number of GPS Outage Reports in EVAIR Database. EVAIR collects reports from EUROCONTROL Member States and a large adjoining geographic area from participating aircraft operators in the Middle East and North Africa. The 2018 increase is mainly linked to events in the Eastern Mediterranean region. No . of reports absolute figures 17 2014 51 2015 494 2016 164 2017 815 2018 GPS Yearly Trends 2014 – June 2018 800 600 400 200 0 FIGURE 2 Number of Events per Flight Information Region (FIR). FIRs are anonymized to enable data sharing. Not shown are many FIR's with no events. If events accumulate in a single FIR, EUROCONTROL coordinates with and supports the State and ANSP concerned through its Network Manager function. Absolute figures - No . of reports A B C D E F G H I J K L M N O P R S T U V Q X Y W Z AA BB CC DD EE FF GG FIRs affected FIRs affected Jan – June 2018 absolute figures 300 200 100 0

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