As its name says, the NDB (Non Directional Beacon) is a non-directional beacon associated with the Automatic Direction Finder (ADF) operating between 190 Khz and 1750 Khz frequencies. It is an old aid but still in use due mainly to its low maintenance cost. It also has the advantage that the NDB signal follows the contour of the ground so its range is usually much higher than for example the VORs, although it is also true that they are more affected by the weather. For more information, see Annex 10, Volume V chapter 3.2 of ICAO.
In the practice that I propose we will arrive at the Airport of Madrid Cuatro Vientos (LECU – LEVS) on the radial 5 – 6. Why these radials? Because they pass approximately by the Point Sierra of the field, one of the entry points (the other is November) of the aerodrome. Anyway you can practice the exercise in any field, just get the charts and a plotter to find the right radial. As I said this is an old aid radio, but I think it is very useful for fields that do not have other radio aids for pilots who have not been these airports before. For example my good friend Manuel told me that after flying from Andalusia (more than 200 NM) they turned around because they were not able to find S of Cuatro Vientos.
I’ve done the practice with X-Plane 10 in the Carenado Beechcraft Bonanza F33A with the SimCoders Reality Expansion Pack plugin which is the plane that I fly lately. Because speeds I do not recommend fly the exercise with faster aircraft, at least until the concepts are more or less clear. The ideal plane would be a Cessna 172 although then you will have to use the chronometer of the cellphone. I have omitted startup procedures, etc., because it is not the object of the practice.
After leaving Point W we ascend to 4500 Ft in heading 270 and after reaching this altitude and move away from the field (IMPORTANT, THE RANGE OF THE X-PLANE RADIO AIDS ARE A JOKE AND SOON THE SIGN IS LOST, TAKE ACCOUNT OF IT IF YOU FLY EXERCISE IN THIS FLIGHT SIMULATOR) we make a few turns, changes of course, etc., to “get lost” a littleAlthough it is not strictly necessary, first we are going to know where we are exactly, for this we are going to take the needle of the ADF to a side, this is, 90º or 270º, in this case I have taken it to 270º We maintain the course and we check the time the needle takes to reach 260º mark, in our case about 90 seconds. Then through a simple formula (Time = Time between markings (in seconds) / 10) we know that we are at a distance of 9 MINUTES. To know the distance in nautical miles it is enough to know the TAS or better the GS applying it to the following formula: Distance in NM to the station = TAS (GS) * minutes between marks / 10. To calculate the TAS we need the CR3, but the use of the computer is not the object of the practice so it is enough to know that we are a little more than 20 NM. of the station. As I said this information is not necessary for the practice I have proposed, but it is very simple and it is useful to know the distance we are from the station, for example my friend Manuel could have known the approximate distance to the NDB and then maybe he would not have had to turn around We are going to start the maneuvers to arrive to the field by the radial 06 of the NDB of LECU (CVT). First of all we maintain the aircraft in the heading of arrival and we check that the ADF mark indicates 10º to the left Then we must turn left 10º of ADF + 30º, I mean as we were heading 060º (the chosen heading for the arrival), we will turn left heading 020º. If the ADF we had 050º right so we would have turn right 50º + 30º = 80º, we always add 30º to the ADF reading. ATTENTION!!! MAXIMUM CUTTING ANGLE 90º Continue at 020º until the needle of the ADF needle marks 060º (chosen arrival heading to the station), starting turn taking into account the indicated speed. In this case we are practically aligned in the radial 060 from the beginning of the maneuver We keep heading and there is Point S (the urbanization to the right of the compass). The ideal would have been to enter between half and a mile to the right of the point of notification, but since it was not the object of the practice I did not take into account the drift From there it is simple, we just need to follow the procedures described in the approximation VFR charts of the field and nice land!