Point to Point Navigation [Archive]

veetwo

7th Dec 2006, 22:22

You have two radials and two corresponding DME's. You wish to navigate from one to the other using only the RMI (ie Point to Point nav). Always remember that your current radial is indicated by the tail of the needle. The larger DME is always imagined to be on the outside edge of the RMI, while the smaller DME is placed proportionally closer to the centre of the instrument.

Example. You are on the 180 radial at range 20 DME. You wish to navigate to the 090 radial at range 10 DME. Your aeroplane is imagined on the tail of the needle. You then draw an imaginery line between the tail of the needle at this moment in time (180 Radial 20 d) and half way along the 090 radial, where you want to go. Half way along because you are going to 10 dme, half of your current range of 20 d. Then, parallel this line through the centre of the instrument and read the heading straight off the edge. You will get something in the range of 030/035 degrees, give or take. Thats your heading to fly!

You then need to continually (every 5 mins or so) re-assess your heading. The technique works better when the two radials are sufficiently far apart that you can perceive the angles clearly. You know when you have arrived because the tail of the needle will indicate the required 090 radial at 10 dme.

What some people do (including myself) is to use point to point to get a rough heading to fly so that you can get going in the right direction, and then plug the radial/dme in to RNAV to get an exact fix. Although it is perfectly possible to do the whole thing using only the RMI, (and it is good practice to do it every now and again) I find it needlessly increases my workload to use it all the way to the fix. If you have the means to reduce your workload, why not use it!!

Hope this helps

V2