Using any two or more radio navigation aids, a pilot can determine their current location. This is known as a position fix and it is a useful backup to visual navigation, particularly if you are unsure of your position.
You can get a position fix from:
If you find your radial (QDR) from two different VORs, your position will be at their intersection.
A fix is easier when the two radials are at roughly 90° to each other.
A position fix from two NDBs is achieved in much the same way as the above fix from two VORs.
A position fix can be done by finding your radial from a VOR and your radial from an NDB. The intersection of the two radials is your position.
A position fix from two DMEs is possible, but more difficult to work out while airborne.
Once you have your distance from two different DMEs, you can draw a circle around each DME. Your position will be where the two circles intersect.
However, this gives two possible positions so you must have a rough idea of your location to know which intersection is your current position.
The easiest type of position fix to do while airborne is with a co-located VOR and a DME. First, find your radial from the VOR and draw it on your chart. Next, measure your DME distance along this line to find your current position.
A co-located NDB and DME can be used to fix your position in the same way as with the VOR/DME position fix.