[lxgr]

I would honestly not be surprised if pure GPS approaches were discontinued in the near future, giving all the spoofing incidents recently, and the shocking vulnerability of avionics systems to them. (I would have expected the GPS/INS to reject highly unplausible GPS signals in favor of the IRS, and huge clock deviations in favor of a simple internal quartz oscillator, but apparently neither is the the case.)

TLS seems much less vulnerable to spoofing, given the signal strengths involved.

The idea of an onboard TLS spoofer seems both feasible and very scary, though, now that I think about it...

[throwaway48476]

It would help if RTK was widely deployed, especially on cell phone towers.

[lxgr]

That already exists: GBAS is the aviation equivalent to RTK. It provides integrity monitoring and differential signals via VHF. It's better than WAAS, since it's ground-based, and accordingly significantly harder to drown out in a large area.

But neither WAAS nor GBAS are authenticated, so are ultimately both are spoofable.