Fix ILS DME (with back-course disabled DME incorrectly only works in the 180 degree front-course)

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Brief description of the issue:
When using Navigraph navigation data ILS are updated to correctly transmit/block the back-course depending on real installation specifics (for example in the UK, ILS do not transmit back-courses). An issue with this is it affects the function of any associated ILS DME.

For ILS without a back-course the associated DME stops working once you’ve crossed the runway threshold (ie. it only works in the front-course 180 degree arc).

This is an issue in the UK at least because generally missed approaches will use the ILS DME and we also we have some airports that have an ILS only to one runway end but use the associated DME in an NDB/DME approach to the other end. Examples would include Southampton (EGHI) and Humberside (EGNJ).

Humberside even includes a DME arc based off an ILS DME which is impossible to fly in the sim using Navigraph navdata:

The correct function should be the DME element works throughout 360 degrees as it broadcast on a separate but linked frequency to the ILS.

Detail steps to reproduce the issue encountered:

  1. Load Navigraph navigation data
  2. Fly past the runway threshold at an airport with an ILS only at one end but with no back-course (e. EGNJ)
  3. The DME stops as you cross the threshold

Build Version # when you first started experiencing this issue:
Present in but I think present in all previous builds

Moved to #third-party-addon-discussion:tools-utilities as Bugs and Issues would only cover stock Navigation Data (i.e., NavBlue) not Navigraph as indicated by the Topic Author.

I appreciate the problem only becomes evident if you use Navigraph however the issue is an underlying problem with how the sim handles ILS DME as opposed to a problem with Navigraph date. The issue is masked in the default sim data which assumes every ILS has a back-course.

My worry with this being moved is it isn’t going to register as a bug report for the underlying sim engine.

In the absence of official acknowledgement by MS-Asobo of this defect, the best way to get this visible is moving it to #self-service:wishlist where it can become voteable (which it just did).


Cheers, sounds like a fair compromise!

Am I correct in thinking that DMEs associated with an ILS are not omni-directional by default in MSFS and only become so if the ILS is attributed a ‘back course’?

If so then that does sound like a weakness in how the DME is set up and therefore I voted for this item.

Seems to be. I gather the default installation has a back-course for every ILS. In the UK (and I think a lot of Europe) the back-course is suppressed/deactivated. The DME is frequency paired but should radiate through 360 degrees regardless of the presence of an ILS back-course. If you install Navigraph data then back-courses are correctly suppressed as per real life but you lose the DME in that 180 degree sector which renders many instrument procedures impossible to fly.

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I just visited EGNJ (Humberside) to check this out. I also use Navigraph data and I see exactly what you mean. Definitely looks like a design issue with how the DME associated with an ILS is implemented in the sim.

I agree this is a stock navaid bug, probably inherited from FSX and earlier platforms. As a retired USAF Ground Electronics engineer I know that the DME is a omnidirectional transmitter/receiver and is not directly linked in any way to the range of the localizer as it certainly is in this simulation.


Newark Airport is another location where this would be a problem. The NEWARK 4 SID for departures off of runway 04L or or 04R uses the 04R ILS (I-EZA) DME to indicate to pilots when they should turn left to a heading of 290 degrees. The distance to begin the turn is 4 miles DME north of the ILS installation and is on “the back side”. Departures off of the 22L or 22R runways use the ILS 22L (I-LSQ) in a similar fashion, with a turn at 2.3 DME flying south.

Quick update, had tested without Navigraph and hadn’t reinstalled.
By chance I’ve spotted that the default navdata correctly supresses the back-course at EGAA (Belfast Aldergrove) for ILS 25 so you lose the DME past the threshold in the base sim alone, so technically it’s a full bug as opposed to just a wish list for Navigraph support.

I suggest filing a bug report to zendesk with as detailed findings as possible for this issue, including your findings for EGAA.

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