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It may not always be obvious to passengers, but GPS has transformed the efficiency of civil aviation. Where once aircraft could only fly in straight lines between specific waypoints and on runway approaches, GPS-based navigation lets them take any valid route to their destination.
Now, that efficiency is under threat from GPS spoofing, a type of malicious electronic attack that’s becoming increasingly prevalent around the world.
In previous blogs, I’ve looked at the impact of GPS spoofing on two key aviation systems that rely on GPS data: ADS-B and eGPWS. For this one, I want to look at the impact on navigation, and the problems it’s causing for airlines, passengers, flight crew and air traffic control.
Aircraft navigation was more restrictive before GPS
Before the advent of GPS, aircraft were required to fly between dedicated VOR/DME radio beacons, dotted across each country. A similar radio beacon-based system, called ILS (instrument landing system), was also used at airports to guide the aircraft’s landing.
While these systems worked well—and continue to work well, as they are still in use—they limit the choice of flightpaths and runway approaches. Flying from one VOR/DME beacon to another isn’t always the most efficient route from A to B, while ILS landing beacons require aircraft to approach the runway from specific, pre-determined angles.
The many benefits of GPS for aircraft navigation
The arrival of GPS swept all of those restrictions away. Its ubiquity meant that waypoints could be created anywhere along the route, giving flight crews and air traffic control more freedom in planning and orchestrating flightpaths. At the airport, GPS meant aircraft could approach the runway from any angle and direction, giving ATC much more flexibility in sequencing landings.
By enabling wider and more efficient use of airspace, GPS has opened up thousands of new routes, enabled airports to handle more arrivals and departures, and reduced fuel burn. It has also reduced stress and radio congestion in the control tower, since ATC can give a pilot a complex arrival or departure procedure and be assured the aircraft will follow it without the need for voice communications.
In the aircraft itself, GPS can be used to help tune avionics to the correct VOR frequencies, to pull up correct navigation charts, to see nearby air traffic via ADS-B traffic, to automatically tune weather radars, and more. Better still, it doesn’t require any special equipment at the airport that’s costly to install and maintain—just avionics capable of receiving and processing the satellite signals.
The role of GPS in backup navigation systems
GPS also has a key role to play in calibrating backup navigation systems. Most aircraft carry inertial navigation systems—often called dead reckoning systems—that can continue to hold a course if radio-based systems like GPS and VOR/DME are temporarily unavailable.
Inertial navigation systems rely on sensors like gyroscopes and altimeters to measure the aircraft’s speed, heading and altitude, and use those measurements to calculate a position. The measurements are highly reliable for short periods, but drift if they aren’t regularly synchronized with an independent source of position data.
As a free, global resource, GPS is an ideal source of absolute positioning data that can be used to calibrate the inertial system. In fact, most aircraft navigation systems now fuse GPS with inertial sensors to form a highly accurate Global Positioning Inertial Reference System (GPIRS).
Unfortunately, though, GPIRS systems are vulnerable to interference if they aren’t adequately protected—and one of the most insidious forms of interference is GPS spoofing.
The impact of GPS spoofing on aircraft navigation
Spoofing is a greater threat to unprotected aircraft navigation systems than GPS jamming. In a jamming scenario, the attacker floods the GPS frequency with electromagnetic noise, causing the receiver to lose its lock on the faint GPS signals. This isn’t ideal, but it’s often not a high-risk threat as the inertial part of the system can take over until the aircraft exits the jammer’s range. Sometimes jammed receivers can act in unusual ways, so it’s important to test against the threat and understand how your systems may be impacted, but the risk is generally relatively low.
In a spoofing attack, the attacker broadcasts fake GPS signals that can cause an unprotected receiver to calculate a wildly inaccurate position. Even though there are redundant GPS receivers, both will feed incorrect data to the GPIRS as well as to ADS-B and eGPWS, meaning an attack can cause all of those systems to start operating with false position data.
The impact of a spoofing attack can therefore be wide-ranging. If it’s not detected, or if flight crew haven’t been briefed that their route will pass through known areas of spoofing, the risks can be high. In the worst-case scenarios, the aircraft can go off course, potentially into dangerous airspace, and there is higher risk of collision with terrain or other aircraft.
Outside of worst-case scenarios, the impact on pilots and flight crews is still significant. Spoofed GPS will mean systems misbehave, and misbehaving systems means increased workload and reduced options and margins. Reading the transcript of the Azerbaijan Flight J2-8243 before the tragic crash shows just how much the workload increases when GPS becomes unreliable.
GPS spoofing is a real threat to commercial aviation
It’s vital for the aviation industry to get to grips with GPS spoofing, as it’s becoming much more prevalent worldwide. While it’s most common in conflict zones, where spoofing forms part of many nation states’ navigation warfare (NAVWAR) toolkits, the equipment and know-how to transmit fake GPS signals are now widely accessible. The flight safety organization OPSGROUP found that around 1,500 commercial flights a day experienced spoofing in July–August 2024, a 500% increase over the first half of the year.
Spirent eBook: Protecting Commercial Aircraft Against GPS Spoofing Threats
Fortunately, it is possible to protect commercial and private aircraft against the risk of GPS spoofing. There are numerous mitigation strategies, from understanding where spoofing is likely to occur and briefing flight crew accordingly, to installing anti-spoofing receivers and antennas.
To help the industry take action, we’ve produced an eBook that dives deeper into the impact of GPS spoofing on commercial aviation. It looks at the risks to airlines and aircraft, and sets out a mitigation roadmap with recommended actions for the immediate, medium and longer term.
You can download it here: Spirent eBook: Protecting Commercial Aircraft Against GPS Spoofing Threats. And if you have any questions, please don’t hesitate to get in touch.
