YSSY - ILS Z or ILS Y PRM 16R?

[Kapitanleutnant]

All….

Scratching my head on this one:

We were cleared the ILS 16R PRM into YSSY recently. There are two approaches into 16R using PRM…. a Z and Y.

We asked which one they'd like us to use and they again stated, "ILS PRM 16R". Asked yet again since we could not determine if they wanted us to use the Z or Y procedure. We were told to standby. Then told it would be ILS PRM Z 16R.

I do know the "Z" is always the preferred approach but my question to you all is….

In the absence of a designator such as Y or Z for an approach, are we to fly the "Z" procedure? And if so, would anyone have a reference for this somewhere?

Thanks

Kap

[kellykelpie]

Z uses IKS DME, Y uses SY DME but the approaches are the same other than this. Nothing written in AIP that I could see so I guess it is up to the preference of the crew as to which fix they wish to use for a glide slope check.

[Keg]

If you're cleared an ILS without specifying which should be used then you have the option of either. For the 767, we'd normally go the Y due to instrument switching but if the SY DME is U/S then the Z is easily doable.

[Oktas8]

Apparently (rumour network!) the SY VOR and DME will be decommissioned once all six ILS's at Sydney have discrete DME frequencies. Then the problem will go away.

In any case, I find it helpful to remember that the sole purpose of a DME on an ILS is to provide a glideslope integrity check. Which particular navigation device is used to achieve this goal is unimportant. Could even use the GPS, if national law permitted it.

[A-Thousand-To-Go]

Not entirely true Oktas8, the SY VOR will be decommissioned from mid-2014, however the SY DME will be relocated 180m from its present position. The reason for the DME remaining serviceable was due to performance limitations of some operators with older machinery.

[Biatch]

Lol.... Seriously???

There is no difference between the two barring which DME you use... As the controller said he's cleared you for the approach... It's left to you which you want to do... You'll only be forced to use one if either DME is u/s at a certain time..

[A Comfy Chair]

Yes Biatch, I imagine he does mean it seriously. Its a perfectly valid question.

Why? Because in other parts of the world (read most/all of the others), you would be specifically cleared for the Y or Z approach, because they are different approaches.

MEL, SYD and BNE there happens to be no issue, as the only change between the charts is the use of ILS vs Airport DME (although why Brisbane is the opposite to SYD and MEL is beyond me). But in many cases that is not the only change between a Y and a Z approach. There could be different minima, a different missed approach, any number of things. They are, again, different approaches.

Its a relevant question for someone who doesn't do Australian airports day in, day out.

[alphacentauri]

SY VOR is being decommissioned permanently


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[alphacentauri]

Welcome to the PBN revolution :)


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[Kapitanleutnant]

OK…..

Thanks for all the replies.

Let me know tell you "the rest of the story":

After landing, and on ground control freq, the ground guy said to us, "no worries on this but approach control would like you to contact them". I said ok will do.

Had the other guy monitor ground while I went over to approach freq. This controller said he just wanted to clear up any confusion. So I said that I just needed to confirm which approach of the two options he wanted us to fly and initially had not given us that information… that was all. Since we were told to fly the "Z" procedure, he then asked what the dates were for our approach plates. I told him and then his reply was, "OK, you flew the right approach then".

And that was it.

So….. the fact that he said we flew the right approach left me even more confused… and thus the question if we were supposed to know to fly the "Z" if they don't give a specific approach procedure as the "Z" is the primary/preferred approach.

I think pretty much every pilot here would have at least queried ATC on which of the two procedures ATC wanted him to fly just to confirm….and I was simply making sure I was doing the right thing.

Kap

[LongLats]

Lol.... Seriously???

Don't be such a Biatch, Biatch.

[nitpicker330]

We have company notams for a couple of ports around Asia for the Airbus fleet advising the crew that the FM database ILS is coded for Y or Z. Just so we can match up the waypoints to the correct chart.

Other than that it's up to you which one you chose to fly as the initial approach and missed approach are generally the same..

HOWEVER some Japanese ports ( and maybe others ) clearly specify on the ATIS which ILS they want you to fly as some of the procedure is different.

"Expect ILS Y 16R, using Runway 16R....." Is usually what you hear on the ATIS.

[Derfred]

I think pretty much every pilot here would have at least queried ATC on which of the two procedures ATC wanted him to fly just to confirm….and I was simply making sure I was doing the right thing.

Incorrect. Pretty much every pilot here would have known that you can fly either approach. Your choice.

[Bladeangle]

Yeh as already stated, it doesnt matter which one you fly, the only difference is which DME you hold/use. The geographic points dont change, just the point from which you measure the distance from does.
Your choice. Same at Wagga, Melbourne and prob plenty more around the place.

With reference to the approach controller stating "you flew the correct approach", vaguely remember the chart index number changing few months back as 16R ILS got its own paired DME. I may be incorrect... He was prob just referring to that.

[Capn Bloggs]

I'm with Defred. I've never queried, and have never heard another pilot query, which ILS, the Y or the Z, to do. You just pick the one appropriate to your DME fit/desire.

If in the future the X and Y procedures are different (as Nitpicker is alluding to overseas) I'm sure ATC will clear us to do the one they want us to do.

[FGD135]

Asked yet again since we could not determine if they wanted us to use the Z
or Y procedure.

Why do you think they would care whether you were using IKS or the SY DME?

... the fact that he said we flew the right approach left me even more confused…
I would say his answer was tongue in cheek. He was saying, in effect, that provided your chart was current, it didn't matter which of the two you used - both were correct.

[RENURPP]

It is a reasonable question and anytime your not sure you should ask as I would and in my opinion any intelligent person would. ATC are capable of making errors as are pilots.

Having said that I would normally search for differences between the ILS's and if they were minor as they are in this case (different DME) I would have made my own mind up.

The aircraft data base is normally predicated on using a particular DME and that makes the decision easy for you, all though you may not discover the difference until you cross check the altitudes etc. (been there done that more than once)

[Counter-rotation]

The OP has asked for an AIP reference for his question, and as far as I can see no one has found one (me included). Can anyone find a reference anywhere? I can only recall (don't have the AIP to hand) mentioning of the naming convention used, when this was introduced in Australia a while back, possibly in a now expired AIC or SUP.

Is this another example of our awesome regulations in Australia - folklore and local familiarity begets procedure that turn into proxy regulation (ie. the only difference is the DME, so if Approach don't specify, you can do whatever you want... "Yeah that's just what we've always done, it must be right".)

As for those saying "the only difference is which DME" well I think you're missing the point somewhat. That may apply in this specific case, but I reckon it's fair to say that the OP is looking for a more general answer, that could be applied in all cases.

And if there's any doubt, of course without exception, you would ask!

[Kapitanleutnant]

Counter-Rotation:

Thanks and you nailed it right on the head as to what I am seeking with my post!!

I can not find anything in my company manuals or other international documents to answer my query.

K

[alphacentauri]

Maybe I can help clear this up....maybe I cannot.

There are 2 issues here. 1. Approach naming and 2. Approach clearances.

1. Approach naming - There was a change to this a few years back and the current ICAO convention is to name the approach according to the navigation aid or system that is providing AZIMUTH guidance. This is why all the DME's were removed form the approach names. Of course the issue that will be arising in the near future is what do you name an approach that starts as an RNAV/RNP and ends in an ILS.....ICAO are still sorting that one out.
Part b to this was that someone declared (and I think it was CASA) that if there are 2 DME's available for a particular approach, then we would have to provide a separate approach for each DME. This is where the ILS-Z/Y's are coming from. My thoughts are that the intent of the Y/Z suffix was to depict approaches that gave separate tracking...like a timed reversal vs a DME reversal or 2 distinct inbound tracks. The result is that we are publishing 2 ILS approaches that are exactly the same on 2 different plates. This is further complicated by PRM...so you have ILS-Z/Y and PRM-Z/Y

2. Approach clearances. Up until a few months back I was told that the approach clearance had to contain the approach title when it was issued. With recent questions to ATC we have become aware that, in the case of Sydney at least, for ILS approaches they just say "Cleared ILS approach". They do this for a few reasons but the main one is that they just don't give a rats which one you fly. If your ILS or PRM clearance does not contain the suffix Z or Y then it is up to you. If you look at the AIP GEN 3.4-45. There is a note in the left column. "...the procedure suffix may be omitted when no possibility of confusion exists." so no-one is breaking any rules here....its just more complicated than it needs to be.

This scenario is being further complicated with the introduction of CAT II/III minima and the insistence that these also be published on separate plates (ie YMML)

The future...CASA has been approached with a solution, which a safety case is currently being compiled for. The proposal is to publish 1 ILS plate, and provide refences to the 2 DME's on it. Provided we can keep it simple I think it would work and we are aware that this is done in overseas locations.

Hope I have answered some questions.

Alpha

[Bladeangle]

Naming convention for procedures, from the ICAO bible...


9.5.3 Duplicate procedure identification

9.5.3.1 A single letter suffix, starting with the letter z following the radio navigation aid type shall be used if two or more procedures to the same runway cannot be distinguished by the radio navigation aid type only. For example:
VOR y Rwy 20
VOR z Rwy 20
9.5.3.2 The single letter suffix shall be used when:
a) two or more navigation aids of the same type are used to support different approaches to the same runway;
b) two or more missed approaches are associated with a common approach, each approach being identified by a single letter suffix;
c) different approach procedures using the same radio navigation type are provided for different aircraft categories;
d) two or more arrivals are used to a common approach and are published on different charts, each approach being identified by a single letter suffix. If additional radio navigation aids are required for the arrival they shall be specified on the chart's plan view. For example:
ILS y RWY 20 (“CAB VOR Arrival” shown in the plan view)
ILS z RWY 20 (“DNA VOR Arrival” shown in the plan view)
9.5.3.3 As some avionics systems are capable of loading only a single approach, States should ensure that the preferred approach is identified using the z suffix.

[Kapitanleutnant]

Alpha…

That's a great explanation and answers a lot!! Thank you!!

I guess my question at this point would be….

If it's up to us to fly either approach, why did the approach controller advise us, "Well then you flew the correct approach"?

Some have said we would be correct in flying either approach in absence of a specific approach, but to me, what the ATC guy said would imply that had we flown the Y approach procedure, it would have been the "wrong" approach.

So far, I've not found nor have I been shown here any documentation in black and white saying something to the effect, in the absence of a specific procedure, you can fly any procedure (ILS specific in this case) you want".

Maybe there is no such thing. Then again, I may be so blind as to not see something already discussed here. :-)

K

[Capn Bloggs]

I do know the "Z" is always the preferred approach but my question to you all is….

In the absence of a designator such as Y or Z for an approach, are we to fly the "Z" procedure? And if so, would anyone have a reference for this somewhere?

The OP has asked for an AIP reference for his question, and as far as I can see no one has found one (me included).
That's because there is no reference because the ILS Z is not the preferred procedure. If it was, it would be written somewhere.

As AC said, "they just say "Cleared ILS approach". They do this for a few reasons but the main one is that they just don't give a rats which one you fly."

Put it another way. On any approach where there is currently a Y and Z option, and ATC hasn't nominated the Y or the Z, would in make any difference to what the aeroplane would do if you flew either? The answer is, of course, no.

[A Comfy Chair]

That's because there is no reference because the ILS Z is not the preferred procedure. If it was, it would be written somewhere.

Well, technically, it should be. That is part of the Jeppesen naming convention for approaches. The preferred approach should be named the Z approach.

On any approach where there is currently a Y and Z option, and ATC hasn't nominated the Y or the Z, would in make any difference to what the aeroplane would do if you flew either?

In Australia, no, in other parts of the world, absolutely.

If I were flying into another part of the world where they had two separate approaches for the same runway, and I wasn't told which one to fly, I'd be asking! A close look at the Australian case and yes you can see there is no difference between the charts, so it makes no difference - but that shouldn't be a default position to take, as we are perhaps being a little unique in that regard.

The reason nothing is written about which to fly when told "cleared ILS" is because the controller should be clearing you for the specific approach - the ILS Y, or the ILS Z. That is what normally occurs when there are separate approaches for the same runway (for example, Japan). It is really no different to being cleared for an ILS vs NDB at MEL - they are different approaches. As are the ILS Y and ILS Z. At the moment, with only the DME the difference between the two, it doesn't matter, and we're assuming we're all on the same page. But it is an assumption that doesn't hold with the global reasons for having more than one ILS approach to a runway.

[Kapitanleutnant]

Thank you Comfy Chair!!

After some more research, a colleague of mine gave me a reference I've been looking for CONFIRMING that the Z is indeed the preferred approach!!

It states:

"If a state identifies two or more approach procedures which are based on the same NAVAID, they are shown with a figure or a letter suffixed as, e.g. ”A”, ”B” but ”One”, ”Two”. Where approach procedure designator suffixes are officially published with "A" or "B", "One" or "Two" respectively ”Z”, ”Y” or ”X”, the primary procedure (usually the standard procedure with the lowest minima) will be identified with the suffix "Z.

So…. now the only question I have is again…. in absence of a procedure to fly, which one would you legally be required to fly? I still say it is wise and prudent to ask for clarification. How can you not… especially as the controllers down under can be a bit demanding…. good, but a bit demanding.

Kap

[Capn Bloggs]

Let's get a couple of things straight here.

1. Are you based in Australia? It would help if we know who we're dealing with.

2. That text DOES NOT APPLY to Australia (not that I can find in our AIP, anyway!). Where'd it come from? Alpha Centauri posted the Australian AIP reference that covers this exact issue.

So…. now the only question I have is again…. in absence of a procedure to fly, which one would you legally be required to fly? I still say it is wise and prudent to ask for clarification.
Nothing in particular! Fly whichever ILS you like; they are both exactly the same (the DME used is irrelevant). The initial replies from ATC indicated that. I suspect that he finally caved in and gave you an answer that wanted to hear.

If we get every man and his dog now asking which one to fly because of this I'll spew... :*

[Bladeangle]

The only reference to it in the Jepp is in Terminal AU-18 (3).

The only time I would imagine a controller clearing you a specific approach (with reference to Sydney) is if you had not specified DME equipment on board your aircraft in the flight notification, obviously then you could only use the PRM - Y with use of GNSS.

[Capt Claret]

Cairns has a LOC-Y RWY 33 and a LOC-Z RWY 33. The LOC-Y is annotated Cat A & B, whereas the LOC-Z is annotated Cat C & D. It's the only approach which comes to mind, where there is a difference between the Y & Z version other than the DME used. The MDA, Viz, Mapt and Mapt speeds are different.

Any time I've been cleared for said approach the phraseology has specified "LOC-Z".

[nitpicker330]

All good unless you fly outside our protected bubble in Oz :D

[Oktas8]

You know what would remove all this confusing rubbish, this "we have to different" business?

Remove from the AIP that reference that prohibits use of GNSS unless specifically authorised, and replace with

"GNSS may be used in lieu of DME in all instrument procedures. When using GNSS in lieu of DME on an ILS procedure, care must be taken to ensure that the correct reference waypoint is used."

The safety implication for using the wrong reference on an ILS is... a 'failed' GS integrity check and a missed approach. You'd do it once, learn from the error and not do it again.

Sorry for the rant. But sheesh, way to make something easy into 20 extra pages in the AIP!

[Capn Bloggs]

It's the only approach which comes to mind, where there is a difference between the Y & Z version other than the DME used.
There are many different Ys and Zs about. Lots of VORs, NDBs eg YPPD 14 VOR, YPKA, YBRM.

[alphacentauri]

GNSS may be used in lieu of DME in all instrument procedures. When using GNSS in lieu of DME on an ILS procedure, care must be taken to ensure that the correct reference waypoint is used

There is a small problem with your theory. Where there are 2 ILS approaches available, one will be referenced off a VOR/DME and the other will be referenced off the ILS/DME. Only the plate referencing the VOR/DME will allow GPS in leiu of DME. The other plate does not allow it. The reason is that DME's are not stored in navigation databases as a stand alone point.

The reference waypoint for any NDB/DME or VOR/DME is the location of the NDB or VOR respectively. They are deemed to be co-located and the difference in physical location is small enough not to cause a problem.

The reference location for any ILS installation is the localizer antenna array. This could be several hundred metres from the DME and as such GPS in leiu of DME is not allowed.

The safety implication for using the wrong reference on an ILS is... a 'failed' GS integrity check and a missed approach. You'd do it once, learn from the error and not do it again.

The saftey implications of using the wrong reference on an ILS are fairly significant I would have thought...in the case of YSSY ILS 34L the reference point giving you distance would be some 2000m from your intended touchdown point....the figures would be way out. Are you going to trust the GS, or the GPS distance numbers, which won't match those on the plate?

[UnderneathTheRadar]

Alphacentauri

Quick question - what determines the -Y and -Z?

For example, most ILS-Z use the ILS DME and the -Y uses the VOR/DME. Brisbane is the other way around - would seem a potential 'gotcha' to me....

UTR

[alphacentauri]

UTR,

Brisbane was one of the first to be published and unfortunately predates the naming convention we have today.

Unfortunately, it's not easy to change under the current data change rules. We can't simply swap them round in one cycle, it would take 3 cycles. The -z would have to go to an -x, then the -y would have to swap to the -z, then the -x would go to a -y....over 3 cycles. Bit confusing and probably safer leaving it as is.

Alpha


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[Capn Rex Havoc]

Capn Bloggs,
Nothing in particular! Fly whichever ILS you like; they are both exactly the same (the DME used is irrelevant). The initial replies from ATC indicated that. I suspect that he finally caved in and gave you an answer that wanted to hear.

A question though- In many of the ILSs overseas the difference in the Y,Z etc lies in the missed approach path. I am not sure if this is the case in Syd.
Would it not be prudent for ATC to specify the letter suffix to ensure the correct missed approach is flown?

[Spotlight]

This is getting really complicated, but the fundamental was the date on the chart, correct?

[alphacentauri]

Guys, it's not that hard.

As has already been pointed out, the only ils in the country that has a difference between -y and -z is Cairns. All others are exactly the same. In the case where they are the same, and no confusion can exist, ATC are not required to specify the suffix. (refer aip)


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[sunnySA]

The "date issue" may relate to this week's update for CAT II approaches.

[Oktas8]

The reference location for any ILS installation is the localizer antenna array. This could be several hundred metres from the DME and as such GPS...

Alphacentauri, not quite. (Yes it's not allowed, as i said.)

For any ILS, there are two reference points in the GNSS database. One is the LOC transmitter as you say. The other is the GS transmitter, which is (approximately) where the DME is. It is possible to select the correct reference point such that the GPS mimics the DME, although of course that would be illegal in Aust! (Not always elsewhere...)

Yes, if you picked the wrong waypoint it could be 2000m or more away from the DME. So? The sole purpose of a DME in an ILS installation is for an integrity check. If it's 2000m or more out, the integrity check will fail. The AIP (rightly) provides for this, but there is zero safety implication associated with an erroneous distance readout unless the GS signal is faulty. Hence the need for this integrity check.