ICAO has outlined a range of initiatives and technical measures being undertaken to counter the threat of interference to satellite-based navigation for air transport.
The weak signals from GPS and other similar navigation satellite constellations make them vulnerable, and there has been a surge in the number of jamming and spoofing incidents – particularly around, although not limited to, areas of conflict.
Several papers submitted to the upcoming ICAO Assembly in September focus on the interference threat.
ICAO’s Council, in a proposed resolution to the Assembly, says interference has become a “recurrent and persistent challenge in several regions”.
It can degrade flight-management position data, disrupt the ability to comply with required navigation performance, lead to map shifts, and trigger false terrain warnings – as well as cause flightpath deviation, increasing the risk of mid-air collision or entry into restricted airspace.
Since satellite-based navigation also provides time synchronisation for communication networks, interference can potentially cause datalink breakdown and lead to ADS-B surveillance gaps.
In the short term ICAO is promoting simpler and more consistent NOTAM information. IATA has identified 18 different NOTAM text remarks for interference, and the paper says this diversity makes searching for warnings difficult.
ICAO has also undertaken development of a standardised implementation pack for mitigating the impact of interference, which is aims to launch in the fourth quarter of this year.
It says this ‘iPack’ – which combines ICAO guidance material and best practices from different regions – will help countries effectively manage satellite-based navigation interference occurrences while ensuring safe and efficient air navigation services.
The pack will raise awareness of interference effects and provide a risk-mitigation framework, as well as assist countries with assessing and “right-sizing” their conventional navigation infrastructure.
Longer-term measures centre on enhancing resilience to interference. ICAO is working toward a concept of complementary position, navigation and timing – or C-PNT – which closely integrates multiple sensors and introduces independent time sources.
This aims to ensure that individual airborne systems cannot corrupt others while achieving a “suitable balance” between autonomous aircraft capabilities, space-based and terrestrial systems, the paper states.
While the paper says the C-PNT actions are expected to be completed by 2030, it stresses that industry commitment and support is necessary for its successful development and implementation.
A more advanced concept – alternative PNT, or A-PNT – would provide solutions which are fully independent of satellite-based navigation systems.
This concept, the paper says, is under review by ICAO specialist groups and could take advantage of advanced inertial navigation, terrain contour matching, star tracking and advanced magnetic navigation.
ICAO is also developing a resilient navigation operational network concept, to support countries in achieving cost-effective and appropriately-sized capabilities through “optimised deployment” of ground-based navigation aids, based on traffic density, aircraft capabilities and operational requirements.
This aims to “better utilise” combinations of available conventional systems – such as VOR, DME, ILS and NDB – to support reversion during periods of interference, the paper says.
Augmentation signals for ground-based augmentation systems which provide differential correction are unencrypted and potentially exposed to falsification. ICAO commenced development of standards for authentication in 2017 and the paper says validation of these standards is foreseen by November 2027.
It adds that the European Galileo satellite constellation is progressing towards navigation message authentication capability, which will show that received navigation messages genuinely originate from Galileo. ICAO standards will be applicable in 2029, the paper states, and a future generation of receivers could support these authentication measures.
Dual-frequency capability across multiple satellite constellations could offer greater accuracy, reliability and resilience, it adds, compared with current single-frequency systems.
“This will also help mitigate vulnerabilities in respect of [interference] affecting a single frequency or constellation, ionospheric disturbances, and the risk of having insufficient satellites within a single constellation,” the paper says, although it suggests that initial operational introduction is not foreseen until 2032-35.
