VOR, GPS and Area Navigation

The VOR broadcasts 360 radials, each a magnetic bearing outward from the station. You select a course with the omni-bearing selector; the course deviation indicator then shows whether you are left or right of that course, and a TO/FROM flag tells you whether the course leads to or away from the station. A crucial point is that a VOR indication does not depend on your heading — it reflects only your position relative to the selected radial. GPS works differently: a satellite-based receiver computes your precise position, groundspeed, and course anywhere, and it enables area navigation (RNAV), which lets you fly directly between arbitrary waypoints instead of station to station. GPS depends on receiving several satellites and uses integrity monitoring such as RAIM, so a prudent pilot keeps traditional navigation skills sharp in case of an outage. Distance measuring equipment (DME) complements these aids by reading out the nautical-mile distance to a DME-equipped station like a VOR/DME or VORTAC. DME measures slant range — the straight-line distance to the station — rather than horizontal distance, so directly overhead a station it shows roughly your height above it, and many units also display groundspeed and time to the station.