TO/FROM Indicator
The TO/FROM indicator on the HSI/OBS for the VOR has confused student pilots for many years but the concept is quite simple if you follow some simple rules.
- The TO/FROM indicator DOES NOT show if you are going to or from the VOR.
- The TO/FROM is independent of the aircrafts heading.
The TO/FROM shows where you are with respect to the VOR dependent on the Course Set on the HSI/OBS
Let’s put this in practice.
Here is an OBS with the course set at 300o. Remember on an OBS we set the course using the OBS knob (sometimes this says CRS), this is the course we want to home into or away from the VOR.
The CDI (Course Deviation Indicator) shows that we are 2 dots to the left of the 300o Radial, as this is a 10-dot scale and full scale on a VOR is 10o, we are 6o Right of the 300o radial.
The TO/FROM is showing FROM.
So, let’s draw what we can see.
1. Draw a line on the course heading (300o) through the VOR. Add an arrowhead to the front to the line and a tail on the back of the line.
- Now draw a line at 90oto the course through the VOR.
- In the area the areas behind the 90o, in the area where the Tail is, write TO as this is the TO area. Write FROM in the areas in front of the line, this is the FROM area.
4. From the CDI we can see we are in the FROM area and we are to the right-hand side of the 300o centre line – look at the line in the direction of the arrow. So, we must be in this Red marked area.
- We are flying a VOR so full-scale deflection is 10°, the inner circle is 2oand as this is a 10-dot scale, each dot is an extra 2o, so in this case we are 6o (Centre + 2 dots).
- Draw a line at 6oin the red area, we must be on this radial.
- From here we can see the QDR (306o) and the QDM (306-180 = 126o).
Remember this indication is irrespective of aircraft heading and if you are flying to or from the VOR, it is where you are in respect to the VOR and the Course you have set in the OBS or HSI.