Navigation by radio aids includes navigation mainly by reference to indications of bearing and distance indicated on VOR, DME and ADF equipment located on the aircraft. This information is derived from ground radio beacons (VOR, DME and NDBs or broadcast stations.)
The simplest form of navigation involves flying a direct track between a succession of VOR or NDB beacons which lie on or close to the desired track (see Figure 1.) This is the form of navigation employed in conventional airways navigation. The magnetic track and distance betwen successive beacons is measured and the calculated heading is flown, with corrections to allow for the effect of wind, until the next beacon is reached. Distance (and elapsed time) to the next beacon is read from DME or calculated by dead reckoning.
1. The route is plotted between radio beacons, some of which may be within controlled airspace; but the aircraft turns onto a pre-calculated track from or to another beacon before the area to be avoided is reached (see Figure 2.)
2. The direct route is plotted without reference to any paricular radio beacons and fixes are calculated along the track based on position lines plotted from radio beacons (see Figure 3.)
In practice, the simplest way of using method 2 is to pre-plot position lines during pre-flight preparation and compare actual bearings or DME ranges with pre-plotted lines (see Figure 4).