LORAN? If they bring back any of the old systems to back up GNSS, I suspect it'll be that. I recall hearing somewhere that Eurocontrol was looking to bring back a minimal LORAN-C infrastructure.Gosh, it's too bad we don't have a nation-wide, ground based nav system independent of satellites, which could pinpoint your location to meters, was a fully automated rnav system, used small inexpensive receivers, and is largely unaffected by solar flares and EMP.
Wait, what is this non-functional radio in my panel.....