ILS/DME Question
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.
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.
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No, DD, you're just using a different point in space.
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!
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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.
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.
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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
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
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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.
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.
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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?
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?
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G'day again DD.
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?
Wouldn't be the first time something like that has happened... 
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...
Very large aircraft may initiate a missed approach/go around at the indicated DA and still actually touch down. Are they breaking any rules?
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?
Wouldn't be the first time something like that has happened... 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...
****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.
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.
