The Risk of Aircraft Navigation Modernization

We love technology. If you’re reading this, you at least can use a computer, possibly have an RSS reader, probably have an interest in geeky things, so I don’t need to go into proving that statement, methinks.

One problem with some new technologies, however, is dependence. Certain technologies become “the way” we do certain things. The “home phone” is all but gone. The magnetic compass has fallen to personal GPS units. Hell, paper maps have fallen to them as well.

With recent legislation, so too will ground-based navigation for aircraft in the US.

[FAA] NextGen will transform the aviation system from relying on ground-based navigation to one that uses new technologies, such as global positioning systems (GPS) and Automatic Dependent Surveillance-Broadcast (ADS-B).

I’ve written letters to my congresspeople about this (letters, which too have been obsoleted by politicians auto-responding with form letters), as it’s a very bad idea. Satellite navigation is an extremely valuable system that definitely should be allowed in the cockpit, but not at the expense of mothballing the terrestrial navigation radar systems.

GPS Constellation

Satellites are big bullseyes. Nearly every semi-modern country from China to the US to North Korea to France to Iran to probably the Australians can shoot down satellites. There are at most 40 GPS satellites in play. That’s only 40 targets. There are several hundred ground-based nav radar installations in the US alone. Nothing short of thermonuclear war is going to wipe those out in one salvo. To make matters worse, while there are at most 40 satellites (probably closer to 30), one does not need to outright destroy all of them, or even most of them, to render the GPS system globally defunct. Just knocking enough of them hard enough to rotate or leave orbit would suffice. In order to have good precision, a GPS receiver needs at least six, but preferably nine-to-twelve satellites in the visible sky, so even just rendering 20-30% of the satellites inoperable will have a devastating impact on the precision and utility of the system.

Lastly, it is trivial to impersonate a GPS signal and deceive listening receivers. The public GPS spectrum is well-known and voluminously documented. You can build a multi-signal transmitter for around $100 and completely disrupt the working system. Someone with a transmitter on a commercial flight could trivially cause course drift, and possibly toy with elevation information. Depending on how much the pilot trusts GPS over the other instruments, very bad decisions could be made. Yes, I’m well aware of the encrypted government-use band. It’s still quite vulnerable.

This change was inevitable: A lot of younger pilots are all for it, as it bottoms-out the instrument learning curve; The government (FAA) is big on it because they will save a lot of money by installing overpriced GPS receivers in exchange for maintaining the nav radar network; and as I already said, the technology is invaluable in the cockpit. My first Garmin receivers, “way” back in the mid-1990s, were designed for cockpit mounting, even. But this technology should be an augmentation, not a replacement. As once pilots become accustomed to it, their ability to navigate will forever be linked to the availability of this high-value, fragile, target.