> (...) I don't believe they need GPS signal on takeoff/landing, they use older tech for that. Much older. The basic "stack" uses radio beacons, not greatly d

> (...) I don't believe they need GPS signal on takeoff/landing, they use older tech for that. Much older. The basic "stack" uses radio beacons, not greatly different from early XX century tech. The more advanced Instrument Landing System is quite a bit more complex, but in very basic terms is a set of radio beacons that define a glide path. It is local, and requires no GPS.