A radial is a magnetic bearing from a VOR station. In a conventional environment, the aircraft used to fly inbound and outbound on radials from the different VOR stations as defined by the ATS route network.
A position estimation can be made with the intersection of two radials. As the angular signal propagates, the splay of the signal increases. Therefore, the precision of the position estimation is a factor of distance from the transmitting stations; this is known as the Dilution of Precision (DOP).
Dilution of Precision
For angular measurements, the DOP is effected by range.
Using a simple mathematical rule, commonly called the 1 in 60 rule, the effect of angular displacement of the transmitted signal can be calculated. The 1 in 60 Rule states:
‘An angle of 1° subtends 1NM at 60NM’
The performance of the transmitting station will clearly effect the accuracy of the position estimation.