ILS/DME

[keithl]

Hi chaps,

If you read my profile you'll see I'm now a sim instructor. Specialising in Procedural IF, one of my standard scenarios is to fail the DME so that crews have practice in the "No DME" procedures, where these are provided. This question is to maximise the authenticity of such exercises.

I know from my local air traffickers that when the ILS fails here, the DME fails with it. I suspect, but do not know for a fact, that this is not the case everywhere. I suspect it varies with the type of equipment.

Can I have a few responses indicating whether your local ILS DME wil continue to respond, after the LLZ and GP elements have failed / been switched off?

[Spitoon]

It probably depends whether the DME is only associated with the ILS. If so, and the way to tell is that the range is usually zeroed to the threshold, without the ILS there is no use for it. Well that's the technical answer anyway.

With no use, it will probably be switched off too, maybe automatically, much as every type of kit I've worked with will not radiate a glidepath if the localiser fails unless an engineer manually switches things on.

Hope this helps.

[Simtech]

On the sims I work on, the instructor has the ability to fail any or all element(s) of the ILS/DME, i.e. the localiser, glidepath and DME can be failed individually or in any combination. I don't know how this stacks up in real life, but the facility is much used.

[Tower Ranger]

If our glidepath fails we do loc/dme approaches, if the loc fails we take the ils off as you can`t use the glidepath without it.
The dme operates independantly from the ils so ndb/dme approaches are available but rarely a thing of beauty..

[Chilli Monster]

DME is independant same as Tower Ranger's - if you lose the ILS you still have a published NDB/DME approach

[keithl]

Thanks, all, that's the sort of info I'm after. It does vary from place to place. Now, if I choose to do an exercise at an a/d unknown to me, is there any way of telling (you mention DME zeroed to threshold, Spitoon) from published info, whether that a/d's ILS DME will fail (or be switched off) if the other elements fail.

In the absence of any such info, I will of course continue to BS as I always have...

[Chilli Monster]

Check out the other instrument procedures in place for the airfield - that would give you a pretty good clue.

For example. If the airfield has an ILS/DME and also an NDB/DME check the small print. If the NDB/DME is not available without the DME element then it's a big clue that it's independant operation (You'd be daft to have to lose your NDB approach if you had the ILS off for tech reasons). If however there is a timed element available to the approach it's possible that the DME is tied to another facility, and as such they've taken the 'failure' scenario into account.

[Capt Pit Bull]

As an observation, regardless of how the aids are set up / associated and turned on or off by ATC, don't forget that failures on the aircraft can deprive the pilot of one or more elements.

e.g. since an ILS/DME is 3 receivers on the aircraft, you could have a failure of the localiser and still have glideslope and DME indications.

Wierdly enough, this happened to me recently. The Nav control box glitched and succesfully tuned the Glide and assocated dme, but instead of the localiser left the nav receiver tuned to the previous frequency, which happened to be a VOR just north of the field.

Just proves the point of the importance of identing aids.


Keithl,

For an interesting exercise, try this. Find somewhere with an NDB and an NDB/DME approach, which have different minima. (generally this will involve a stepdown fix that is related to the NDB only minima, to get you past a limiting obstacle). Have the student fly an ndb/dme approach. Once they are past the final stepdown fix (i.e. they are now below NDB only minima) fail the dme. Most people will go around, but in fact it is quite reasonable to continue to the original minima. Incidentally, this is not a silly exercise - it actually hapened to me - on my initial IRT !!

CPB

[NATCA BNA]

Keith,

Here in the U.S. if the DME portion of the ILS fails then we tell the aircraft when they are over the FAF. The DME outage doesn't take out the entire ILS if air traffic control can call the FAF.

Mike
NATCA BNA