English
Satellite signals from the Global Positioning System (GPS) play an increasingly important role in commercial aircraft. As well as making navigation more flexible and efficient, data from GPS also feeds into other core avionics systems, including enhanced ground proximity warning systems (eGPWS) and Automatic Dependent Surveillance-Broadcast (ADS-B).
But growing use of GPS in the cabin means the risks arising from a GPS malfunction are also increasing. While many things can interfere with GPS signals—from solar storms to man-made radio frequency jammers—one of the most disruptive threats is signal spoofing.
Spoofing is the (usually) deliberate act of broadcasting fake GPS signals to trick GPS-reliant systems into thinking they are somewhere else. In an aircraft, a spoofing attack can have a range of negative impacts, from triggering spurious ground proximity warnings, to causing false information to be broadcast to air traffic control and other airspace users.
In this blog, I want to look at the impact of spoofing on ADS-B particularly. I’ll show why ADS-B is vulnerable to GPS spoofing, the impacts it can have, and why airlines should take steps to protect against attacks.
ADS-B plays a key role in efficient air traffic control
ADS-B enables an aircraft to communicate its position to air traffic control (ATC) and other nearby aircraft. It’s now mandatory in the US and numerous other countries for commercial and private aircraft when flying in controlled airspace.
Whereas radar – also used by ATC – can only determine an aircraft’s position, ADS-B transmits additional useful information including flight number, registration, altitude, speed and heading. It consists of a transponder that takes position data from the aircraft’s GPS receiver, and automatically broadcasts it along with the other information. Since the broadcast is public, it can also be received by other aircraft and receivers on the ground.
Air traffic controllers rely on ADS-B to know which aircraft are in their airspace—or on the ground at the airport—at any given time, and where they are in relation to each other. This allows ATC to sequence takeoffs, landings and taxiing, maximizing efficiency while leaving enough separation between aircraft to ensure safety. ADS-B also provides contextual information for voice communications between ATC and the pilot.
A secondary, and important, use of ADS-B is that it can help military personnel to determine whether an aircraft is ‘friend’ or ‘foe’. A passenger aircraft broadcasting its flight number and registration can easily be identified as a ‘friend’. An aircraft that is not transmitting identification details via ADS-B may be suspected of being a ‘foe’. Although ADS-B is not the only technology used for this purpose, its pervasiveness and ease of use means it does often play a role.
What happens when ADS-B experiences a GPS spoofing attack
While ADS-B is an extremely useful system, it can only be useful when it’s receiving accurate and reliable information from GPS. If something happens to the GPS signal, ADS-B may either stop working completely, or start outputting dangerously erroneous information.
If the aircraft enters the range of a signal jammer—a powerful radio transmitter that floods the environment with electromagnetic noise—ADS-B may simply stop broadcasting, because the aircraft’s GPS receiver can no longer pick out the GPS signal.
When it enters the range of a signal spoofer, the effect can be far more insidious. If the aircraft’s receiver locks on to a false GPS signal, the ADS-B will start reporting the aircraft’s position at the co-ordinates given by the spoofed signal, rather than its actual position.
The consequences of ADS-B impairment for air traffic control
This has obvious consequences for ATC, which can no longer rely on the information it normally uses for efficient flight sequencing, ground operations, and, in some cases, runway incursion prevention. During a spoofing attack, aircraft and ATC must fall back on direct pilot communications, legacy systems where they still exist, and primary radar (if the area has coverage). In some cases, there is no way for ATC to determine the location of the aircraft and they rely on the pilot position reports, which are degraded without reliable GPS! Often, this results in ATC ensuring greater separation between aircraft reducing the airspace efficiency. The economic impact for the industry is felt in the form of delayed flights, cancellations, and higher fuel burn.
If the aircraft and ATC are unaware that a spoofing attack is happening, there is a high risk of confusion, stress, and disruption until the attack is confirmed and alternative measures put in place. And if defense forces are unable to identify an aircraft as friend or foe because its ADS-B position does not match what they are seeing, the risk of military intervention increases.
GPS spoofing is a real threat to commercial aviation
This can all sound like science fiction, but GPS spoofing is now a daily reality in commercial aviation—particularly since it’s now a common navigation warfare (NAVWAR) tactic in conflict zones and other contested territories. Globally, Spirent detects over 1500 flights a week that are spoofed - primarily in Europe, the Middle East, and Asia.
Spoofing is therefore a risk that the commercial aviation industry can’t afford to ignore, and indeed I and others at Spirent are having regular conversations with airlines and avionics manufacturers about how it can be addressed.
Spirent eBook: Protecting Commercial Aircraft Against GPS Spoofing Threats
To inform those conversations, we’ve produced an eBook that dives deeper into the impact of 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.
