GPS Spoofing Now Takes Avionics In Its Clutches

Business and commercial aircraft are being led astray thanks to their sensor-fused navigation systems. A series of spoofing incidents beginning in late September has caused complete aircraft navigational system failures in some airliners and business jets overflying the Iraq- Iran area.

GPS Spoofing

“What we’ve seen since late September,” University of Texas researchers say,” is unprecedented. We have never seen commercial aircraft captured by GPS spoofing before.” The GPS spoofing has continued and as researchers at the University of Texas at Austin (UT Austin) have sought to pinpoint the sources of the nefarious GPS broadcasts, they have realized that aircraft sent off course by these signals are entirely “captured” by receiving corrupt GPS data which ends up corrupting their backup inertial navigation systems (INS) as well.

“That means that the backup system is no longer reliable as a backup,” Todd E. Humphreys, director of UT Austin’s radionavigation laboratory. Humphreys and a graduate student used “observables” obtained from low earth orbit (LEO) satellites to fix the location of a GPS spoofing signal broadcast during the September time period when a series of incidents was first reported.

Not long after the series of September spoofing incidents Humphreys’ team noted a new source of GPS spoofing in the region emanating from Israel. It picked up a “chirp jammer” broadcasting what Humphreys describes as a sort of “sawtooth” signal. He identified the Israel Defense Forces as the source of the spoofing, likely initiated to keep precision-guided missiles and rockets employed by Hezbollah off balance. The activity was covered in reporting by Israel’s Haaretz newspaper. The IDF subsequently acknowledged the jamming and though against international agreements, it has been recognized as a necessary defensive measure. Notably, it has the same effect on aircraft avionics.

Inaccurate Positions

Within the Collins system and similar systems like Garmin’s G5000 integrated flight deck, the received GPS data is “fused” – passed directly to the INS portion of the FMS which uses the information to update itself, correcting for the natural drift that inertial reference sensors have and calibrating to the same position that GPS is indicating.

“The GPS receiver eats up that false data and generates erroneous outputs,” Humphreys says. The spoofed signals have thus fooled both the GPS and INS navigation subsystems within the FMS. The resulting inaccurate position information may then be passed on to the aircraft’s autopilot, fuel/range calculation and synthetic vision subsystems among others. Spoofing has effectively captured the airplane and its crew as happened during the incidents reported in September. “This was as dangerous as it gets,” Humphreys affirms. “Pilots were as lost as they could get. They had to call air traffic control and ask for turn-by-turn directions. Requiring the GPS and INS portions of integrated avionics systems to check each other, comparing disparities in position information and calculations may seem common-sensical but “it’s not integrated in our current avionics,” Humphreys acknowledges. He points out that such cross-checking must be done rigorously, accounting for both spoofed GPS signals and the natural positional drift that comes with INS.

Humphreys pointed out that Europe’s Galileo satellite navigation system now includes digital signatures that go with the data it sends to GPS receivers to authenticate their veracity. Similar ideas have been proposed for GPS but as yet not acted on. Even then, they are not foolproof. Until fixes for the lack of cross checking in navigation systems and GPS itself are made, the danger to commercial and business aircraft from captured avionics as a result of GPS spoofing will remain high. “I think there are some people who make these avionics systems who are slapping their foreheads right now, saying, ‘We probably should have paid more attention to that failure mode and we didn’t,” Humphreys concludes.

Did you subscribe to our daily newsletter?

It’s Free! Click here to Subscribe

Source: Forbes

• 
• 
• 
• 
• 
• 
• 
•