Question about ILS/DME bias



During approach procedure, if I tune an ILS/DME where the DME is located near the end of the runway, but is configured to give a 0.0nm range a runway threshold, after a passed the threshold and as roll towards the end of the runway, will the DME indication will start increasing or it will remain 0.0nm???



DME = Distance Measuring Equipment.

It doesn’t know what direction you come from. So, it counts down to 0 and once you pass the point it measures from, it counts up.



Thanks Allen for your answer.

I’m talking here about a biased DME. This means the DME signal has been tweak to give a 0 range at runway threshold even if the DME is located 1 to 2 nm at the end of the runway. This king of configuration is common in Europe and not in USA.



I’ve never heard of such a thing. The real question is, if you’re right next to the transmitter, will it show zero, or the distance from you to the threshold. I don’t know how that would be possible.


Since you are busy either landing or on a missed approach at that point, don’t know what it says. Since ILS beams are very narrow, I’m guessing that their is no reading at all unless there is a backcourse with DME (which I’ve never seen).

I’m curious what you would do with the DME info is you had it.


KSMX has DME on their backcourse approach.


For one, you can cross check your alt against your position to insure that you are not following a faulty ILS glideslope. This series of 3 videos explains it MUCH better than I can, but the GS is not actually a signal, but a null between two transmitted signals. A GS indication of “ON TARGET” occurs when the receiver is not receiving these secondary signals. In rare cases (such as in the video) when the primary signal is present, but the secondary signal is absent, the GS needle is centered, and no other warnings are given, REGARDLESS OF ACTUAL ALTITUDE. Many (most?/all?) approaches give DME readings and the corrosponding altitudes from either the primary ILS or other local navaids. *

*Not the opinion of an actual pilot, but one who eagerly awaits ones from actual pilots, so as to learn a little bit…


While it doesn’t answer the original question (from what I can see) there is such a beast… (biased DME) as I just learned today…