In the realm of aviation safety, the emergence of GPS spoofing poses a formidable challenge, distinct from traditional signal jamming. While jamming disrupts satellite signals, spoofing introduces deceptive signals to aircraft navigation systems, leading to potentially dire consequences. This article explores the defensive and offensive applications of spoofing technology by both state and non-state actors.
One important distinction we have to make is that Spoofing is not the same as Jamming. GPS signal jamming is nothing new, and nowadays has become a non-event. Check your NOTAMs and you’ll find plenty of GPS and WAAS outages across El Paso, Texas and some regions over New Mexico and Arizona. Jamming blocks the satellite signal from reaching you. Most advanced aircraft self-address the issue; they automatically disconnect the GPS and rely instead on their IRS and ground-based NAVIDs. You’ll hardly feel the disruption. Then, there is GPS Spoofing. This relatively new tactic sends erroneous signals to your aircraft, tricking it into thinking its 100nm off in a different location.
Although we haven’t seen specific states or non-state actors admit for using this technology, its defensive, and possibly offensive, uses are numerous. Rudimentary cruise missiles heavily rely on GPS and INS for navigation sources. Spoof their signals and these missiles may quickly turn into dumb bombs. Long-range drones have also entered the modern warfare, and the easiest way to kill their out-of-line-of-sight capabilities is by killing their GPS receivers’ integrity. You can find these spoofing techniques employed in all modern conflict zones. The interactive map below shows areas where GPS integrity has been compromised.
The cues that result from GPS spoofing will vary between aircraft. Some common issues include erroneous UTC clock readings, shift in GPS location, and MFD or PFD warning flags. In more advanced aircraft with heavily intertwined systems, more anomalies might surface, including:
Here's what that looks like:
So why does the airplane go completely haywire over corrupt GPS? Simply stated, modern aircraft heavily rely on satellites for everything. GPS is one of the most accurate nav sources, and other systems will often discredit their own inputs and realign themselves to agree with the satellites. Hybrid IRS/GNSS equipped aircraft are also at risk, as these systems are programmed to automatically update their location using GPS. In normal scenarios, this logic works great, and coupled with WAAS (Wide Area Augmentation System), has resulted in pin-point accuracy.
Modern pilots are too dependent on GPS as well. Children of the Magenta Line – we’ve all heard it before. But even the FAA seems to think that pilots need a back-to-basics approach with navigation training. In January 2024 the FAA published a SAFO alerting operators and pilots to brush up on their conventional ground-based NAVID skills.1 When was the last time you flew “green needles?”. In 2019, Rockwell Collins FMS units on certain aircraft, including the CRJ 200 and Boeing 717, experience a GPS glitch that rendered GPS navigation useless. Some airplanes’ MELs allowed for deferral of the units under the condition that VOR/DME/NDB become the sole method of navigation. Hundreds of flights had to fly entirely on Victor and Jet airways, VOR to VOR all across the United States. Are your VOR inspections and tests up to date?
Back to spoofing. For hybrid IRS airplanes, which constitutes the majority of modern civilian airplanes, it’s not just switching to ground based NAVIDs that’s imperative, but it’s also disconnecting the GPS from your FMS altogether. Some pilots have reported that disconnecting the GPS quickly allowed them to resume NAVID navigation just fine. However, wait a couple seconds too long and the airplane’s IRS will reset, detect an anomaly, and might block you from reverting to green needles. Time to cozy up with some light reading on your FMS’s User Guide.
The best course of action is to plan ahead. Identify possible high-risk airspace, continuously crosscheck position, employ dead-reckoning techniques as backup, monitor systems closely, and be very comfortable with your FMS and green-needle techniques.
With corrupt GPS, reliance on ATC for help can be the only way to avoid flying into a war zone. But is that even a viable solution? Firstly, how is ATC locating your aircraft? Primary Radar or ADS-B? ADS-B has many flaws, including easily corruptible and unprotected signals – more on that on a later day. But spoofed GPS signals might also corrupt ADS-B outputs. The FAA identified the effect of corrupt ADS-B on Air Traffic Management Infrastructure, which has resulted in airspace infringements and route deviations.2
The second question to ask is how far did the spoofer go with their plan? VHF radio communication is another very easily intercepted signal. Aircraft comms utilize Amplitude Modulation (AM) Very High Frequency radio waves. VHF radio transmitter/receivers can be bought very cheap. There is zero protection from outside intruders issuing false commands to civilian aircraft, or simply transmitting static to block all other transmissions. Wide spread CDPLC usage can counter that threat, but it still has not been deployed everywhere yet. Ultimately, situational awareness is imperative when flying close to critical areas.
Military aircraft navigation manufactures have already developed solutions to GPS issues. Honeywell, for example, has introduced several robust designs over the years. They integrated their IRS with Vision Aided Navigation that compares a live camera with a terrain map database that yields remarkable accuracy. The system acts as a high-altitude equivalent to cruise missiles’ Terrain Contour Matching – TERCOM – which uses a contour map of the terrain to compare it with an on-board Radar Altimeter. Other solutions include using Celestial Aided Navigation to track stars, and even a Magnetic Anomaly Aided system that measures Earth’s magnetic strength to compare with a global magnetic database. Regardless of the solution, these military grade systems are an added expense, weight, and complexity. Perhaps this should spark a reconsideration to the decommissioning of VORs and other ground NAVIDs across the United States and elsewhere as a quicker, albeit less sophisticated solution.
The rise of GPS spoofing demands a proactive and flexible response from all involved. As we adapt to the changing landscape, it's crucial to stay vigilant and innovative. By strengthening our defenses, improving training, and working together, we can tackle the threats posed by GPS spoofing and other emerging issues head-on.
