Going dark: Navigating when satellite network fails

Modern aircraft are reliant on the signals from Global Navigation Satellite Systems (GNSS) to feed their different systems. Since February 2022, there has been an increase in jamming or possible spoofing of these GNSS systems that may have an impact on aviation safety. On 17 February, EASA issued a Safety Information Bulletin (SIB 2022-02) on GNSS outage leading to degradation in aircraft navigation or surveillance.

The impacted areas

The issue of GNSS jamming is particularly a problem in places near conflict zones where you may be routinely operating. Following an EASA collaborative analysis, the main affected regions are:

The Black Sea area:

• FIR Istanbul LTBB, FIR Ankara LTAA
• Eastern part of FIR Bucuresti LRBB, FIR Sofia LBSR
• FIR Tbilisi UGGG, FIR Yerevan UDDD, FIR Baku UBBA

The southeastern Mediterranean area, Middle East:

• FIR Nicosia LCCC, FIR Beirut OLBB, FIR Damascus OSTT, FIR Telaviv LLLL, FIR Amman OJAC, northeastern part of FIR Cairo HECC
• Northern part of FIR Baghdad ORBB, northwestern part of FIR Tehran OIIX
• Northern part of FIR Tripoli HLLL

The Baltic Sea area (FIRs surrounding FIR Kaliningrad UMKK):

• Western part of FIR Vilnius EYVL, northeastern part of FIR Warszawa EPWW, southwestern part of FIR Riga EVRR

Arctic area:

• Northern part of FIR Helsinki EFIN, northern part of FIR Polaris ENOR

The issues that GNSS jamming and/or spoofing could lead to

The analysis showed that the problem occurred in all phases of flight. In some cases, they lead to re-routing or diversions. It isn’t possible to predict GNSS interference or its effects. Also, the magnitude of any impact depends on the location, duration of the jamming and the phase of flight. The main thing is to be aware of where jamming is most likely, what could happen to the aircraft and what crews can do in that type of situation.

Here are the main issues that jamming could generate in your operation:

• Inability to use GNSS for waypoint navigation;
• Loss of area navigation (RNAV) approach capability;
• Inability to conduct or maintain Required Navigation Performance (RNP) operations, including RNP and RNP (Authorization Required) approaches;
• Triggering of terrain warnings, possibly with pull up commands;
• Inconsistent aircraft position on the navigation display;
• Loss of automatic dependent surveillance-broadcast (ADS-B), wind shear, terrain and surface functionalities;
• Failure or degradation of ATM/ANS/CNS and aircraft systems which use GNSS as a time reference;
• Potential airspace infringements and/or route deviations due to GNSS degradation.

The recommended actions

EASA recommends a number of mitigation measures for operators, ANSPs and National Aviation Authorities (NAAs). These measures should be considered for operations in the areas mentioned earlier in the article and extended to any other areas identified. A new version of the SIB will be published if the situation changes.

Air operators, including helicopter operators, should consider the following actions:

Reporting:

• Immediate Reporting: Ensure that flight crews promptly report any observed interruption, degradation or anomalous performance of GNSS equipment or related avionics by means of a special air-report (AIREP) to air traffic control.
• Follow-up Reporting: Ensure that flight crews report full details of what happened through your organisations management system. As an operator, ensure the report is shared with your NAA – this will help to keep EASA updated.

Risk Assessment and Mitigations:

• Operational Risk Assessment: Assess if GNSS jamming and/or spoofing poses a risk to your organisation based on where you operate and your level of reliance on on-board systems requiring inputs from a reliable GNSS signal;
• Determine Mitigations: If required, in the flight planning and execution phase you should consider the availability of alternative, conventional arrival and approach procedures (i.e. an aerodrome in the affected area with only GNSS approach procedure should not be considered as destination or alternate).
• Dispatch Limitations: Ensure that operational limitations introduced by the dispatch of aircraft with inoperative radio navigation systems in accordance with the Minimum Equipment List, are considered before operating an aircraft in the affected areas.

Flight Crew Awareness:

• Make sure your flight crews are aware of possible GNSS jamming and/or spoofing, particularly if they are flying in the areas referenced at the start of the article.
• Remind them to verify the aircraft position by means of conventional navigation aids when flights are operated in proximity to the affected areas.
• Check that the navigation aids critical to the operation for the intended route and approach are available and;
• Remain prepared to revert to a conventional arrival procedure where appropriate and inform air traffic controllers if such a situation arises.

Actions for NAAs:

• Ensure that contingency procedures are established in coordination with ANSPs and airspace users, and that essential conventional navigation infrastructure, particularly Instrument Landing Systems, are retained and fully operational.
• Implement appropriate and proactive mitigating measures as a matter of high priority, including the issuance of NOTAMs e.g. describing affected areas and related limitations (as appropriate and determined at State level).

Finally, NAAs and ANSPs should also do the following:

• Establish a process to collect information on GNSS degradations, in coordination with the relevant National Communications Authorities, and promptly notify the related outcomes to air operators and to other airspace users.
• Confirm ANSPs’ readiness to provide reliable surveillance coverage that is resilient to GNSS interference, such as ground NAV aids for conventional non-satellite based navigation (Distance Measuring Equipment (DME), Very High Frequency omnidirectional range (VOR)).
• Ensure that ANSPs' contingency plans include alternative procedures to be followed in case of large-scale GNSS jamming and/or possible spoofing events.