ILS/DME Question

[HEALY]

A bit of background first, using the Perth TCA. The Rottnest Twin NDB appch indicates that if DME at Perth is US then radar will provide radar distances for you....Question

You are ILS equiped but NOT DME or IFR GPS equiped. Inbound to Perth and Runway 03 ILS/DME is being used. If conditions are below circling minima appch ie use R24 ILS or for traffic flow reasons can you request or except radar distance readouts at the key points in you R03 appch.

Forgive me if there is an obvious answer to this but I have not found a reasonable answer yet.

[404 Titan]

HEALY

The RWY 03 ILS at Perth in an ILS/DME approach. There are no marker beacons for this runway otherwise it would be called the ILS, ILS/DME RWY03. AIP 7.2c states that if markers aren’t available then another means must be available to do the altimeter check on the glide path. AIP DAP 1.1 states you can’t use any navigation facility not on the plate to do the approach. So in answer to your question, no you can’t use Perth Approach radar to obtain the necessary DME distance to do an Altimeter check for wry 03. When I was still flying in Australia, I remember some rule that stated to do an ILS you had to have DME and/or Marker Beacon receivers. The AIP and DAPS don’t look the same as they did a few years back and I can no longer find that reference.

[chimbu warrior]

404.............can't speak for the DAP's, but the section you refer to is addressed in Jeppesen Terminal AU-17 paragraph 3.1

It is too lengthy to reproduce here, but basically covers what you said.

[Piston Twin]

Don't the full reason, but had this discussion with the Perth TCU a few days ago, and for whatever reason they are not permitted to give radar distances on the 03 ILS.

PT

[QSK?]

AIP ENR 1.5-32 para 7.2 “ILS Failures” refers.

Interesting subject this, as I also have a question with respect to the non-availability of DME on an ILS approach, which is a slight variation on the original question.

The above reference provides guidance on the procedures to be followed in the event of a failure of any of the ILS sub-system components ie the Locator, GP and Markers. Failure of the Locator or GP equipment is understood, however, I note that some locations have ILS approaches that don’t consist of Marker Beacons eg Albany R14 (WA), Perth R03 and Sydney R34R. These approaches rely on DME or GPS for distance to threshold and a failure of a DME in these instances does not appear to be covered by AIP. Therefore, my question is this:

What happens if you’re in IMC, cleared for (of commence if OCTA) the approach and the DME fails when you are halfway down the LLZ? Obviously, common sense would dictact immediate application of all the “ups” and the commencedment of a climb to (at least) the 10nm MSA whilst maintaining track guidance via the LLZ, although I can’t find an actual AIP reference to support this action in the event of a DME failure.

Under AIP, a pilot cannot commence the missed approach (tracking) procedure until the MAPt has been reached, however, how does one determine where the MAPt is without the DME (assume no GPS available), as the MAPt is normally indicated as a DME distance from the threshold? In a radar environment (eg the Sydney R34R or Perth R03 ILS), I guess the controller would most likely take responsibility for your missed approach and obstacle clearance by radar vectoring you onto the missed approach track above the minimum radar vectoring altitude. But what happens if the airport is uncontrolled, outside of radar coverage and the missed approach track is not a continuation of the LLZ track (luckily at Albany the missed approach track is also the LLZ track)? Or wouldn’t an OCTA ILS procedure be designed with a missed approach track that was offset to the LLZ track?

Whilst Jeps may be specific on this issue, I agree with HEALY - I can't find a specific reference in AIP re the procedures to be followed in the event of DME failure whilst conducting a no-marker ILS approach.

Enlighten me, someone, please!

[OzExpat]

QSK?... taking first things first, the guidance issued here is to identify the MAPt by DR... the well known SWAG (scientific wild-ass guess). Yes, there are problems with this but, as you will have initiated the climb prior to reaching the MAPt, there should be a fairly good margin for error. I had to do it once and, as soon as I'd recovered from a feeling of being completely alone and totally vulnerable, I managed to come up with a rough timing to the MAPt and it all seemed to work out okay.

It's not something that I can recommend tho. I didn't involve the controller in helping me to locate the MAPt because I was far too busy with the climb and time calculation. In any event, I was below the minimum vectoring altitude when it all went pear-shaped, so there was nothing that an ATCO could have done for me straight away.

It is not unusual for a turn to be specified in a missed approach, even with an ILS or LLZ procedure. The fact that you have to make a guess as to when to make that turn is a problem but, again, as you've started climbing prior to the MAPt., you will probably have some sort of error margin to work with. In my case, I didn't have to worry about that as I already knew how far away the hill was and had plenty of error margin to work with.

I take it that your company has no written procedures to cover the situation that you've described? Might be time that they gave it some thought. I reckon that CASA would probably expect that.

[Piston Twin]

Unfortunately with the Perth 03ILS, GPS is not permitted in liu of DME as the DME is co located with the GP, not the Perth DME. From my discussion with the TCU, the missed approach proceedure with a failed DME would be to maintain the LLZ track and thence runway heading, from which Radar Vectoring will be issued.

PT

[QSK?]

OzExpat:

Thanks for the response.

I notice that on US and UK plates that I have seen, there is a box that gives times from the FAP to MAPt for the various GS. Why don't the Oz plates contain same? Also looking at US guidance notes on how to conduct an ILS, they all seem to recommend the pilot time the approach from the OM.

To answer your question, I'm not with any airline or charter company - just a PPL coming to the end of my MECIR training.

[OzExpat]

QSK?...

Why don't the Oz plates contain same?
I don't know for sure, but guess it's for much the same reason that I don't put timing on PNG's charts. The fact is that, it makes a huge difference to the area that needs to be protected in the missed approach. That extra protection area invariably means that more and higher obstacles have to be considered in the design. This can lead to the need for a higher MDA.

Maybe you should ask the flying school if they have any SOPs for the situation that you've described. If not, you could ask the CFI what action he/she would expect you to take.

[Hugh Jarse]

Under AIP, a pilot cannot commence the missed approach (tracking) procedure until the MAPt has been reached, however, how does one determine where the MAPt is without the DME (assume no GPS available), as the MAPt is normally indicated as a DME distance from the threshold?
For an ILS, the MAPt is the intersection of the glideslope and the Decision Altitude. DME is irrelevant (apart from your glideslope check), unless you're doing the LLZ/DME, which is often printed on the same plate and depicts the MAPt for that procedure. ;)

[QSK?]

OzExpat/Hugh Jarse:

Thanks for both responses, much appreciated.

OzExpat, yeah I did consult my CFI on this question but he wasn't too sure either, hence my initiative to go to PPrune to access the wider wisdom of the world. Appreciate your inputs, particularly as I notice that you're a procedure designer.

Thanks, HJ you're right about the positiion of the MAPt but how do I determine the MAPT if, as I indicated in my earlier posting, the DME fails after I have commenced the ILS approach, and I immediately commence (before reaching the DA) a climb to the MSA which takes me off the GP? All I have now is the LLZ tracking guidance and my altimeter. I'd be interested in how you would fly such a missed approach, either against any published guidelines (if there are any) or simply based on your flying experience.

[404 Titan]

QSK?

You also have a watch. I routinely do mental calculations in my head for minutes and seconds to MDA or DA once on the approach. It only has to be a rough estimate as you will already be climbing and clear of obstacles at the MAPT if the DME fails.

[QSK?]

Thanks 404.

Yeah, as you and OzExpat have confirmed, the timer seems to be the logical answer. Guess I'll have to start developing the good habit of estimating the time to MDA/DA on each approach.

Cheers QSK?

[Hugh Jarse]

Thanks, HJ you're right about the positiion of the MAPt but how do I determine the MAPT if, as I indicated in my earlier posting, the DME fails after I have commenced the ILS approach, and I immediately commence (before reaching the DA) a climb to the MSA which takes me off the GP? All I have now is the LLZ tracking guidance and my altimeter. I'd be interested in how you would fly such a missed approach, either against any published guidelines (if there are any) or simply based on your flying experience.

Tough question. I think you mean how would you navigate to the point at which you would turn, if the ILS required one during the missed approach (as opposed to continuing to the DA and going around from there, then turning)? I can't find any reference anywhere. The timing analogy has good merit.

Another aspect we could look at is if the DME fails before or after the glideslope check using an ILS/DME (in comparison to an ILS which only needs marker beacons, ie 16R YSSY or 16 YMML). From a practical perspective, if I had done my glideslope check using DME, and decided to continue (ie, no discrepancy), then the DME were to fail, I'd probably elect to continue to the DA, assuming a valid Glideslope was available. If not visual at the DA I'd carry out the published missed approach. Bear in mind that the DME is primarily there (ILS/DME) for fixing the IAF and glidepath check in the absence of marker beacons on the ground or in the plane. Once past the glidepath check the DME really has served its purpose.

On the other hand, if the DME were to fail prior to carrying out the glideslope check, then I'd go around.:ok: This is where Titan's procedure would work well, particularly with respect to obstacle clearance.

I'm open to suggestions:E

[OzExpat]

From a procedure design perspective, there's only a finite number of ways to identify the MAPt and still maintain procedure integrity. That makes it impossible for regulators to specify an escape methodology, so the best you'll find in official documents is something along the lines of "ya'll be careful now"! :eek:

However, from a logical perspective, most of the latest generation of aircraft can easily exceed the 2.5% missed approach climb gradient, even in a OEI situation. This gives them a huge advantage in obstacle clearance and a consequently greater margin for error in guesstimating the location of the MAPt. Perversely, of course, the latest generation aircraft are also equipped with RNAV and or GNSS capability, making it much simpler to positively identify the MAPt location very accurately.

So it all comes down to the older, lower performance aircraft, especially those in GA, which may not be so well equipped. I can't think of a better justification for installing an IFR-certified GNSS receiver in those aircraft. The fact of the matter is that, while timing can be useful and will probably get you out of trouble, the calculation is invariably pretty rough and the risk of error is consequently huge. But, of course, it's better than nothing... but not much.

[4dogs]

Folks,

My understanding of the use of radar as a substitute for DME is a little different - unless the approach is designed to the appropriate containment area and therefore is titled "RADAR VOR RWY 12" as was the case for Jeppesen plate 13-2 at Adelaide, then radar distances are not able to be used.

HJ, as for the missed approach point for the ILS, I don't think that it always the intersection of the GS and the DA in practice since many plates very specifically ident the MApt as the MM. If you do not have a serviceable DME or IFR GPS in those cases, I do not think that you can conduct the approach.

Stay Alive,

[Hugh Jarse]

Gidday 4Dogs,

Bet you use Jepps (like me).

The MAPt for an ILS is indeed the intersection of the Glideslope with the DA (or DH/RH). I don't have my Jepps with me but if you take a look at the AIP stuff, the MAPt on their charts have (LLZ) at the MM/equivalent DME distance. Jepps omit that information on their charts, which can lead to uncertainty.

Sure, when you fly an ILS in anger, you will get to the DA around the MM (actually past it), but in the strict sense it still is an altitude/glideslope thing as far as I'm aware.

To clarify, take a look at 16R or 34R ILS at YSSY. If you were to go around at the MAPt depicted on the chart (LLZ), assuming you are on slope, then for 16R you would be at approx 350', and for 34R, 480'. The DA for 16R is 220', and for 34R 290' respectively.

Hope this helps.

[4dogs]

Huge,

You are quite correct!

I think that little cabernet-induced brainfart add-on of mine proves that I was much better at drinking than at thinking. I guess I can add another subject to the rapidly increasing list of things I clearly know ****-all about!

Stay Alive,

[Hugh Jarse]

I don't mind the odd glass of merlot myself:cool:

I would be happy to take any spare bottles you might have lying around off your hands. Purely as a means of preventing further "brain farts" of course.:8

[DownDraught]

Well I'm Confused at the replies.

As far as I am aware a MAPt only applies to non precision approaches, and DA/RH apply to precision approaches. For an ILS app the DA is an altitude, not a point on space, so if you reach your DA and are not visual, you must carry out a missed approach. So in the case of a DME failure for an ILS, the distance is not needed, if you are within tolerances on GS and at your DA.

AIP ENR 1.5 1.10.1

$0.02

[Tinstaafl]

DownDraught, the DA *is* a point in space not much different from any other point in space. It marks the intersection of three planes of position.

If you're on the LOC then you've established your position somewhere on a vertically oriented plane aligned with the LOC.

If you're on the GS then you've established your position somewhere on a plane originating at the GS antenna & sloping up at whatever the GS angle is for that installation.

If you're at a particular altitude then you've established your position somewhere on a surface that parallels the pressure setting set on the altimeter subscale (or WRT to the ground below the MAPt if using a radar altimeter).

Without the altitude/height information you could be anywhere along a line of position formed by the intersection of the LOC & GS.

[DownDraught]

Disagree, if you have a PEC chart then your DA is at a different alt then one that doesn't, therefore are you saying the "point in space" moves?

Cheers

[OzExpat]

No, DD, you're just using a different point in space.

[DownDraught]

No, DD, you're just using a different point in space.
That's the whole point!


If you do not/can not apply PEC to the published DA than you must add 50 feet to the published DA. (ENR 1.5 - 1.18.2)

So what are you saying, there is more than one MAPT for any given ILS DA. It is simply an altitude when reached that a missed approach MUST be carried out if not visual. How can we have a MAPT on any ILS that is different for any given aircraft?

eg. ILS Published DA=300ft

Aircraft 1 (A1) applies PEC and has a DA of 301 ft

Aircraft2 (A2) has no PEC chart so DA is 350 ft

What you are describing is that a MAPT for A2 is 49ft above, and therefore further away from the runway than A1, which is why the DA is an altitude and not a fixed point in space!

[OzExpat]

I've never seen a better argument for having a PEC chart, DD. But, no, the fact is that the aircraft "A2" in your example might actually be at 250 feet when the altimeter indicates 300 feet. The thing you need to keep in mind is that the DA accounts for obstacle elevation plus a height loss margin for "sink thru". So, if the pilot does not add that 50 feet margin, there's chance of collision with an obstacle.

In practice, the "point in space" for A2 will be pretty much the same as for A1, it's just that it will SEEM to be different because of the possibility of an adverse error in the altimeter. I guess that I should've put a "smiley" against my previous post because it was said with my tongue firmly wedged in my cheek.

However, without a PEC chart, you will never know if the error in your altimeter is negative, positive of zero. If it happens to be zero then, yes, you'll be 50 feet higher than the actual DA. If it is negative, you could conceivably be even more than 50 feet above the DA. Of course, if the actual PEC is anywhere between 0 and 50, then you could end up being somewhat higher than 300 feet, at DA.

So, in those cases, yes, you'll end up at a different point in space and that's just bad luck - which gets back to my opening comment about a good argument for having a PEC Chart.

[DownDraught]

OE, My original post was to say two points in the discussion.
1. MAPT's do not exist as such for ILS approaches, they are applied to NPA's only.
2. The DA for any given ILS is an altitude.
References to these were supplied.

Clarification

A MAPT usually has 2 things, an altitude, typically the designated MDA, and a reference point, typically passing the Aid, or a distance derived from the Aid. Typically you must not descend below MDA until visual.

MDA allows for the clearance above any obstacle within the circling area.

DA is not an MDA, but rather an altitude when a decision must be made to land or carry out a missed approach. Some aircraft will descend below DA after initiating a missed approach. An ILS provides a means of keeping the aircraft on the intended flight path for an approach, of which, we can assume obstacle clearance is guaranteed, ie the normal landing profile.

Your last post

you said " the fact is that the aircraft "A2" in your example might actually be at 250 feet when the altimeter indicates 300 feet."

It might be, it might be at 350 ft. I don't understand your point, if the aircraft is within glideslope tolerances, than obstacle clearance is guaranteed, no matter what the indicated altitude? (assuming of course no ILS errors)

I agree that in my first post I should have written "fixed point in space" rather than "point in space", after all, anywhere is a "point in space"!

Cheers

[OzExpat]

I'll refrain from commenting on the basic aspects of procedure design that you've mentioned. I deal with that, in considerable detail, every day of the working week.

When I said... "the fact is that the aircraft "A2" in your example might actually be at 250 feet when the altimeter indicates 300 feet", I was alluding to a potential maximum error of 50 feet in the example aircraft's altimeter. In other words, the difference between indicated altitude and actual altitude.

I agree, to a point, that when established on LLZ and GP, you are guaranteed to have obstacle protection. But that protection is only guaranteed down to the DA, minus "sink thru" margin. So, in your example of an ILS approach with a 300 FT DA, you must initiate the missed approach there and then, if not visual - you must not allow the aircraft to descend to 250 feet; even the Regulator obviously cannot allow that.

Neither of us has mentioned whether we're dealing with a Cat 1, 2 or 3 approach and this will make some difference, maybe quite a lot of difference, depending on THR elevation. If I assume that it is a Cat 1 approach to a sea level airport, the standard DH is 200 feet. If the THR elevation is 50 feet, then the standard DA would be 250 feet but, as this DA is 300 FT, it is obviously being influenced by an obstacle somewhere in the precision segment.

In that case, you will not know whether the obstacle is located before the threshold or after it. In either case, if the aircraft is allowed to descend to 250 feet (ie 50 feet below DA), there is a possibility of collision with that obstacle.

Now then, back to the altimetry side of the situation. No pilot in his (or her) right mind will intentionally go below a DA but it can still happen if the altimeter has an error. If the altimeter is over-reading the altitude, and the pilot is unaware of it, the aircraft will continue to an indicated altitude of 300 feet and, at that point, could actually be at 250 feet.

This is the problem. This is why PEC is important. This is also why a Regulator has to prescribe some form of action in the event that PEC isn't available to the pilot. If you're actually complaining about a perception of the arbitrary nature of the 50 feet additive, due to lack of PEC data, that's a different complaint entirely.

[DownDraught]

I agree on PEC and do not have an issue with any points raised, I used PEC as an example to explain DA.

Lets assume CAT 1

In your last post you stated

" So, in your example of an ILS approach with a 300 FT DA, you must initiate the missed approach there and then, if not visual - you must not allow the aircraft to descend to 250 feet; even the Regulator obviously cannot allow that."

This is the point I wish to clarify about DA.

Very large aircraft may initiate a missed approach/go around at the indicated DA and still actually touch down. Are they breaking any rules?

If this is the case, should not the DA be calculated on performance issues as well, ie if it takes an extra 300ft altitude to acheive a climb gradient of 2.5%, then ad 300 ft to DA, so in the quoted case the DA would in fact be 600ft.

This is where the docs (australian) do not seem to reflect what is done in practice.

Personally I agree that the DA is an actual MAPT, however AIP ENR 1.5 1.10.1 (c) states otherwise, and is contradicted in AIP 1.5 2.6.1 (a).

And just to add a bit more on Obstacle Clearance Altitude.

ENR 1.5 1.17.1 (a) States that a missed approach must be initiated at this altitude to ensure compliance with the appropriate obstacle clearance criteria. Now I assume that to be DA.

And the we read in ENR 1.5 1.10.1 (note 2) That we should adjust the DA to provide a climb gradient of 2.5% at the DA.

And to top it all off ENR 1.5 8.1 States "Published ILS CAT I DA and visability minama are availiable to all aircraft except that:" and then vis requirements!

So, I never thought I see the day when I wrote dribble like that, but still it begs the question on DA.

Should you adjust DA, after PEC adjustments, to acheive a 2.5%climb gradient at the adjusted DA to create a final DA? 1.5 8.1 seems to indicate no, but 1.5 1.10.1 seems to indicate yes!

In real life though DA is not increased due to performance is it?

[OzExpat]

G'day again DD.

Very large aircraft may initiate a missed approach/go around at the indicated DA and still actually touch down. Are they breaking any rules?
I can't recall the height loss margin for Cat D/DL off-hand but the margin and minimum DH are intended to avoid that, especially in a Cat 1 approach. I have an idea that the Cat D sink-thru allowance is somewhere around 60 metres. If so then, if the runway is the controlling obstacle, a height-loss margin of 60 metres would round-out the calculation to a DH of 200 feet for standard Cat 1 ILS minima.

In that event, yes, it is legal for them to touch down during the go-around.

As to your references to the Oz AIP, I don't have one and don't apply it here, so am as perplexed as you are! You're undoubtedly not looking for guesses on this but the best I can offer is that, perhaps, the conflicting references were written by different people? :eek: Wouldn't be the first time something like that has happened... :D

I feel sure, however, that it's not the AIP intention to require double-dipping with the PEC. Basically, if you apply it to the DA and can make the 2.5% climb gradient, no further DA adjustment is necessary. A different story, of course, if you can't make the gradient.

As to basic climb performance, the procedure design provides time (i.e. distance) to establish the climb gradient. You will never know how much distance you have unless you want to get seriously involved in Pans Ops. That's why you find wording that tells you to execute the missed approach without undue delay, or words to that effect.

This will only keep you safe, however, if you can climb the aircraft up a gradient of at least 2.5%. Obviously, if you are in a situation where climb performance is degraded - and provided that you are aware of it well before reaching DA - the only way to keep yourself safe is to increase your DA to an altitude that will allow you to clear all obstacles in the missed approach.

I don't want to get involved in discussing that side of the performance problem tho... :ooh:

[404 Titan]

****su-Tonka

Could you possibly give us a reference from your manuals because the Australian AIP’s and Jepps definitely don’t say this? They make it very clear that you can’t replace one aid for another if it isn’t on the plate.