Plotting — Page 478, Lesson 476

Let's start with the plotting symbols and the shorthand that ties radio navigation into your chart work. These Q-codes are the language of direction-finding, and you'll see them constantly. QTE is the true bearing of the aircraft from a DF station. So if a Direction Finding station tells you your QTE, they're giving you the true bearing from them to you. QDM is the track (magnetic) from the aircraft to the DF station. Notice the contrast — QDM is magnetic, and it's the track you would fly to reach the station. QDR is the bearing (magnetic) of the aircraft from the DF station. So QDR is magnetic, and it's the bearing from the station to you. Now, the VOR versions. A VOR Radial is sometimes referred to as VOR QDR — it's the magnetic bearing of the aircraft from a VOR beacon. And VOR QDM is the magnetic track from the aircraft to a VOR beacon. So the radial is what the VOR tells you about where you are relative to it; the QDM is the reciprocal you'd fly to get there. One more term before the symbols: Isogonal — a line on the chart joining places of equal magnetic variation. And Convergency — the angle between two selected meridians at a given latitude or latitudes. Now the standard plotting symbols. These are the ones you should always use, and always record the time of each occurrence. A position line at 1115 UTC is plotted as a true bearing. A two position line fix at 1121 UTC — that's where two position lines cross to give you a fix. A radar fix at 1510 UTC. And a DF station, VOR, NDB or VDF facility has its own symbol. Now the simplest form of plot. You get it by plotting the positions of two fixes. Provided the aircraft has been flying a single heading during the interval between the fixes, a straight line joining them represents the track. That's Figure 28.1, Track Made Good. A track determined this way — between two fixes, with only one heading flown in between — is called a Track Made Good, or TMG. You measure it on the chart in the usual way. And the distance measured along the TMG gives you a method of calculating the actual ground speed. In Figure 28.1, the distance flown in 30 minutes is 100 NM, so the actual ground speed must be 200 kt. That's the whole point — the TMG gives you both your true path over the ground and your true speed over the ground.