| > It's unclear to me how the plane is navigating though if the GPS is jammed. Very weird... RNAV (or aRea Navigation) based on VOR-DME has been a thing since (at least) the 1970's. You put in a waypoint based on a radial and distance from a navaid, and then the box in the cockpit would Do Math so you could follow a track to/from that virtual navaid. Bendix even made a cute little box for small airplanes in the 1980's that allowed you to pre-store up to 4 (or 10) such waypoint-frequency tuples and cycle through them to approximate a straight path from your origin to destination, using navaids near (but not on) your route. Given the service volume of a typical VORs, the 10 waypoints could enable a flight segment of over 2,000 km before you needed to enter more waypoints. Around the same time, the flight management systems in airliners began to have navaid databases, allowing you derive lat/lng from the angle and distance. They could even auto-select the best local navaid to use. That enabled DME-DME area navigation, which has ~10x better precision than VOR-DME. The flight management systems in modern airlines of course still have these databases and support navigation by ground-based navaid. Russia still operates their version of LORAN (Chayka), too, so that's another option. By the 1980's, LORAN receivers were pretty well automated and directly produced lat/lng outputs. LORAN has worse accuracy than GPS, about ~400 meters, but is still good enough to get you to the airport. And, as several other people have mentioned, virtually all airliners continue to carry an INS. |