This page is a copy of a post I made on Frugalsworld quite a long time ago. It's also available on simtechnique in french and on Escadron 111 in spanish.

There are two ways to pinpoint an exact location in F4 as far as airbases or airstrips are concerned:

1. The airbase has a Tacan station collocated - to fly to it you select the tacan channel and follow the bearing pointer to the station. You'll end up overflying the airbase.
That's where you see this line in the TCN list: SEOUL 046X 25 110.9 19/01 18/36 105 37°22N 124° 13'E

- 046X is th Tacan channel - you select it with the T-ILS button on the ICP and then by entering the channel on the ICP scratchpad, see the SP manual for further info.
- 25 is the TCN range 25Nm means it's a terminal area tacan only for approach and not wide navigation.
- 110.9 is the ILS frequency, It's selected automatically when the associated tacan channel is entered - note that ILS is activated automatically after having contacted the tower.
- 19/01 18/36 are the runway orientation
- 105 is field elevation in feet
- 37°22N 124° 13'E are the latitude and longitude for the field. Usefull for entering the coords in the DEST page of the DED if you want to make that selected location appears as a steerpoint in the flight computer.

Now when you enter a tacan channel in the system, you have to use the HSI (Horizontal Situation Instrument) to navigate. That's the instrument below the body attitude.

First switch the HSI on TCN mode using the HSI mode button on the left panel of the instrument. it means the HSI will work according to the inputed TCN. NAV mode means it works relative to the selected steerpoint.
Now, Each tacan emits 360 radials. One for each degree of the circle. Each radial is a half line starting from the station to the infinity. It means that for instance the radials 30° and 210° are on the same direction but are definitely two different radials.

With the HSI, you select a radial with the CRS knob. the value of the radial displays in the up right corner of the instrument. When a radial is selected, the CDI (the needle in the intrument centre) gives you your deviation relative to the radial.

In this example, you're flying a heading of 270 with radial 300 selected and the radial is on your left side. As 300 - 270 = 30 you have an attack angle on the radial of 30°. It means you are approaching the radial with a 30° angle. As you approach the radial, the deviation of the CDI will start to decrease until it's centred. At that point, it means you are on the radial. If you want to follow it, you have to turn to a heading of 300° and keep the radial centred.

Now this is a basic course on radio navigation because obviously, there are much more concerns such as to TO/FROM indicator meaning if you're flying TO the station or FROM the station. That information is given by the red triangle on the instrument. More to come on that later.
Here is a picture that might help understanding the big picture: It's been taken for an alignement on a runway:

2. The airbase or airstrip has no collocated tacan and then it's position is given by a radial from a known tacan in the vincinity and by a distance indication given by the DME (Distance Measuring Equipment) which is in the up left corner of the instrument. The distance given is the distance in Nm between your actual position and the selected station.

So in the tacan list you'll find:
Kojo HS 09/27 180 R135° 054X Dme25 38°48.04'N 125°17.84'E

- 09/27 is runway orientation
- 180 is field elevation
- R135° 054X Dme25 is the airbase location.
It means the airbase is on the Radial 135° FROM Tacan 054X (WONSAN) at a distance of 25 Nm.
So you have to fly to Wonsan using the above method, directly to the station, when overflying Wonsan, you select Radial 135°, center the CDI and keep it centred. It means also that your heading should also be around 135°. It depends on how wide your turn above the station will be. Don't go turning to a heading of 320°, that the wrong side and may leads to confusing readings.
When the DME shows 25 Nm with a centred CDI, you are above Kojo HS.
With a little experience, you'll be able to skip the overflying of the known Tacan station.
-38°48.04'N 125°17.84'E is the latitude and longitude of the airbase/airstrip.