DME (specifically EGCC)

[EGCC Rwy 24]

Although my question relates to EGCC, it will be exactly the same elsewhere. I suspect (hope) the question is significantly longer than the answer!

Arrivals
Aircraft will be on the ILS (I-MM or I-NN) on 109.5 MHz which is frequency paired with a DME indication on CH 32X.

"Zero range indicated at the THR of runway in use". I interpret that as meaning the DME is electronically "moved" to look as if it is at the threshold.

Therefore "160 to 4 DME" effectively equates with four miles from the threshold of the runway in use.

Am I right so far?

Departures
All the SIDs have turns based on DME from MCT. Presumably this DME kit (CH 82Y) is colocated with the MCT VOR, and it is from there that the distances are measured?

If so, that would explain why the turns when departing from 24 are at slightly longer distances than the turns when departing from 06 - because the VOR/DME is nearer to the 24 threshold.


I think I have more or less worked it out --- either that or I am entirely wrong!!



Technicalities
This bit may not be a one word answer. On the idea of a DME being electronically moved from its real position to a runway threshold, presumably this can only be done sensibly when it is frequency paired with an ILS. I can grasp (I think) the concept of a DME being moved a few hundred yards in terms of its responses, but can only see how this would work for a DME which is intended to be used from one direction of approach. Maybe Tech Log for that one?


Clarification welcome.

Thanks,

Nick

[vintage ATCO]

Nope, popular misconception, even by pilots! :D

The zero indication is a hemisphere that passes through both thresholds thus regardless of the selection of the ILS the DME will read from the nearest threshold. The zero range is not 'moved' when the ILS is changed ends.

I had an extremely long conversation with one airline (no names, no pack drill, it was several years ago) who were making allowances when turning on SIDs using DME distances from the ILS!!


VA

[EGCC Rwy 24]

Thanks Vintage - that makes sense, except I am struggling to imagine the hemisphere that you are painting! Unless we are talking about "half a globe" with the flat part laying on the ground?

If that's what it is, then I guess there is a zero indication out to a certain distance from the DME in all directions - in effect "anything less than xxx yards is zero"?

Still need to clarify that on ILS, distance is from the threshold, whereas on SIDs, distance is from the VOR/DME??

Keep it coming!

Thanks

[vintage ATCO]

Thanks Vintage - that makes sense, except I am struggling to imagine the hemisphere that you are painting! Unless we are talking about "half a globe" with the flat part laying on the ground?

Well, hemisphere is used in the definition (Annex 10??)

Still need to clarify that on ILS, distance is from the threshold, whereas on SIDs, distance is from the VOR/DME??

Depends what DME is used in the SID. If it is a co-located ILS/DME, like many are, then the distance is from the threshold even the upwind one, this is allowed for in the SID. If it is a VOR/DME distance, then it is from the facility. Remember too, that it is slant range but not a great deal of difference at SID levels.


VA

[EGCC Rwy 24]

Thanks again Vintage.

I think that clears up the approach vs SID discussion. The Manchester SID plates are clear that the distances are MCT x DME, so that's from the VOR/DME location, not from the threshold.

You mention Annex 10 ---- dare I ask Annex 10 of which publication and is it going to be on the Internet somewhere?

...and thanks for the reminder re slant distance!! I had forgotten that but as you say, for a SID, not going to make a great deal of difference.

Nick

[vintage ATCO]

ICAO Annex 10 Aeronautical Communications Volume 1 Radio Navigation Aids. Well, you did ask. . . . ;)


VA

[EGCC Rwy 24]

Phew! I got as far as the table of contents before it wanted my money --- that was daunting enough!

Thanks for the pointer.

Nick
Nick Locke's Reporting Points (http://www.nicklocke.co.uk/points)

[BN2A]

The reason for the longer time for the turn on the SID's is that from 24R you turn at 3d (24L turn at 3.2d), on 06L you turn at 1.2d all based on MCT. Avoids Knutsford and Stockport.

:cool:

[EGCC Rwy 24]

My site (http://www.nicklocke.co.uk/Points) is now sporting a few more photographs of beacons.

More pictures from all you folks welcomed with open arms (I'm going to struggle to do the whole country on my own)!

Also, information on Reporting Point history seems to have dried up a bit recently. There must be some more out there!

What's next? Someone mentioned the other day that I don't have any pictures of the "points" - he specifically mentioned DAYNE..... Halfway through explaining that there was actually nothing there, I hesitated and realised that I could always take a photo of the exact spot on the ground........ Now, then again, that might just be too mad.

Nick

PS - Thanks to Chiglet for pointing out that Trent DVOR was photogenic - shame we chose a murky day to visit!

PS - Thanks to someone else for pointing out that the Liverpool L-NDB was lurking behind a garage. Without that information, I don't think I'd have believed what I was looking at!

[bagpuss lives]

I've actually visited the spot on the ground that is DAYNE. I realise that makes me very very sad indeed and I can't even defend myself by saying I had good reason.

Didn't take any pictures though - sorry :D

I'd love to see you take a few snaps of LIVPO, KELLY, GINIS et al ;)

Ohhh and whilst I'm here :

LIVPO is soon to be renamed as it's too similar to Liverpool - confusion has ensued on more than one occasion. Keep your eyes and ears peeled ;)

There is a point called RUGER that I don't see anywhere on your site? It's directly North of BAROS, just south of the B3 centreline and is another entry / turn fix for the LIVPO hold.

There's also TORGO, south west of KEGUN and north west of REXAM. Another entry /turn fix for the KEGUN hold.

Hope these help a little :)

[Spitoon]

Dunno whether the zero ranged DME thing is still open to confusion but, just in case, here's a bit more.

If a runway that has an ILS at each end and a DME that is zero ranged to the threshold, the DME will be halfway between the two thresholds. In the simplest of terms, without worrying about slant ranges and stuff, the timing of the signal that the ground station emits is adjusted so that the two (eqidistant) thresholds look to the aircraft like they are where the ground station is and read zero.

The best way to try and describe the hemisphere is to imagine an aircraft coming at the airport from any other direction - the aircraft would also see zero on the DME when they get to a distance that is half the length of the runway away. Similarly, if the aircraft flies directly overhead the mid-point of the runway at a height that is half the length of the runway, the DME will read zero.

Hope it helps.

[EGCC Rwy 24]

Spitoon, yes that helps thanks. It confirms my mental picture of the hemisphere, as described earlier in the thread, to be correct.

Thanks for the input.

That said, I wonder how it works in a situation like Manchester with four thresholds - perhaps two separate DMEs, one for each strip of tarmac?

Nick
Nick Locke's Reporting Points (http://www.nicklocke.co.uk/Points)

[Spiney Norman]

EGCC Rwy 24..Yep, your absolutely correct. There are two TDME's at Manchester to provide the zero range for both runways. (Even though, of course, there is no ILS on 24L).

Spiney.

[LostThePicture]

I suppose it proves useful when someone want to make a VOR/DME approach to 24L though... ;)

LTP

[Spiney Norman]

LTP. You're spot on. The VOR/DME approach for 24L is primarily published for use of the MCT VOR/DME but in the event that the DME associated with the VOR is u/s then the I-MC DME may be used.

Spiney

[Pilot Pete]

Just to add a little more confusion to the melting pot..............

From a flyer's point of view flying reasonably 'big metal', during a SID such as a Honiley out of Manchester we read the plate and then turn earlier(by about 0.2nm) to ensure that the aircraft actually is starting the turn at the said VOR/DME distance!

This obviously depends on how tight the turn is and how big the aircraft is that you fly (due to the inertia.)

PP