DH/MDA with Rad Alt...
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DH/MDA with Rad Alt...
A little clarification requested here WRT an ILS...
AIP ENR1.5.5.1.1 (!)
(my bold)
There is no definition for RH inAIP GEN 2.2.2 There is however a defintion of Radio Height in the definitions of AIP GEN 2.2.1
Now if we were to use this RH (published on our DAP IAL charts in non bold to the right of the DH) as our DH (as the first quoted reg implies) and:
1. This RH is the height above ground beneath the aircraft
2. The RH appears to be predicated on the difference between the threshold elevation and the DH
3. The DH is displaced (for cat 1 anyway) about .5nm from the threshold of the runway.
What about the case where the ground slopes down from the threshold of the runway? Could not this lead you to initiate your missed approach below the DH? Or is this already factored in? Or am I splitting hairs?
Then I ask the question again with respect to an non-precision approach. There the MDA is often a mile or more from the threshold where there is every chance that the terrain slopes up or down from the airport.
CS
AIP ENR1.5.5.1.1 (!)
A pilot must not take off or, except in an emergency, land or continue an approach below the prescribed DA, MDA or RH for the approach being conducted when any element of the prescribed meteorological criteria is continuously less than the minima for the aircraft performance category (CAR 257).
There is no definition for RH inAIP GEN 2.2.2 There is however a defintion of Radio Height in the definitions of AIP GEN 2.2.1
Now if we were to use this RH (published on our DAP IAL charts in non bold to the right of the DH) as our DH (as the first quoted reg implies) and:
1. This RH is the height above ground beneath the aircraft
2. The RH appears to be predicated on the difference between the threshold elevation and the DH
3. The DH is displaced (for cat 1 anyway) about .5nm from the threshold of the runway.
What about the case where the ground slopes down from the threshold of the runway? Could not this lead you to initiate your missed approach below the DH? Or is this already factored in? Or am I splitting hairs?
Then I ask the question again with respect to an non-precision approach. There the MDA is often a mile or more from the threshold where there is every chance that the terrain slopes up or down from the airport.
CS
AFAIK the use of RH for a precision approach requires a radio altimeter operating area that extends a minimum of 300m before the threshold, is 60m wide and has minimum longitudinal slope changes. You're not going to get an RH for a non-precision approach.
G'Day CS,
As I understand it, RH, being radalt indicated height, isn't what you would base your missed approach decision on unless it was specified that way on the chart, and I haven't seen that used in Australia.
The thing I would use as a cue to initiate a missed approach if not visual would be arrival at the pressure altitude nominated as the DH in bold on the chart, and use the RADALT by setting the low bug to HAT and cross checking on the way down.
That passage referring to RH in ENR sounds like one of those general all-encompassing statements they like to use, which can lead to a bit of confusion!
For a non-precision approach, RH will vary with the terrain for a constant run-in at MDA. We used to set it at the appropriate obstacle clearance height on a non-precision approach, again as a guide, ie 400 ft for Cat B.
Others may do differently, I guess, but as I see it, RH shouldn't be used for decision making purposes (unless of course it indicates a gross error from what you expected to see, taking into account the terrain on final).
Cheers
As I understand it, RH, being radalt indicated height, isn't what you would base your missed approach decision on unless it was specified that way on the chart, and I haven't seen that used in Australia.
The thing I would use as a cue to initiate a missed approach if not visual would be arrival at the pressure altitude nominated as the DH in bold on the chart, and use the RADALT by setting the low bug to HAT and cross checking on the way down.
That passage referring to RH in ENR sounds like one of those general all-encompassing statements they like to use, which can lead to a bit of confusion!
For a non-precision approach, RH will vary with the terrain for a constant run-in at MDA. We used to set it at the appropriate obstacle clearance height on a non-precision approach, again as a guide, ie 400 ft for Cat B.
Others may do differently, I guess, but as I see it, RH shouldn't be used for decision making purposes (unless of course it indicates a gross error from what you expected to see, taking into account the terrain on final).
Cheers
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Stallie - can't help you with the query, other than the points already raised (some of which were news to me, but I don't got one of them new-fangled gizmos anyway) and the obvious cross reference to the Ops Man for the Operator; but just curious (given your recent plethora of technical q's) are you lining up for an interview with someone......? Best wishes if so......hell of a commute though.....?
Stallie,
I respectfully suggest to you read and think about what is stated in the "IAL Legend" section of the Australian DAP's.
The height included next to the altimeter(ie pressure) minima is either, for an ILS, the height above the threshold, or for a non precision approach , the height above the aerodrome, at the minima.
You must not assume that this is the height above ground level immediately below you, for example the ILS at Nowra is an excellent example of how radio altimeter heights on a Cat 1(that's all we have in Oz) are absolutley not to be used as a minima/decision height. For those of you who are not familiar with Nowra, probably most non military pilots, the terrain at Nowra is such that the airfield is about 400ft AMSL located on a plateau; the approach flys up a valley and at the minima you have about 400-500ft on the RadAlt; seconds, and I mean seconds later, the aircraft will encounter rapidly rising ground as the valley ends and you cross the ridgeline, the ground then drops to the threshold.
If you where to attempt to use the RadAlt on this approach, which of course would mean disregarding the altimeter, and breaking more than a few rules and good airmanship, you would probably be very dead very quickly. It was suggested in the commissioning report of this particular ILS that there should be some notes included in the approach about this, but they were not.
There are a few other approaches in Oz where the terrain could lead you into trouble if you use RadAlt's incorrectly as well, eg Essendon.
With respect to non precision approaches, the second height stated is the height above the aerodrome. So, the terrain could do anything between the minima and the threshold. However, if you read the AIP ENR 1.5, 2.3 "Approach design concept", you'll find that the approaches are designed for a stabilsed decsent rate. The procedure designers do, I believe( I have talked to them previously regarding how they work things out) take into account the terrain clearances within the appropriate tolerances to the minima, to continue the approach to land you must be visual, so you avoid terrain with your eyeballs as the primary terrain clearance alert; circling approaches assume you will circle to land.
The RadAlt is of course a useful tool, if used correctly, as a cross check or crude terrain warning.
Another point well worth remembering is those paragraghs in AIP ENR 1.5 1.7.2 regarding "pilots should familiarise themselves with the location and altitude of obstacles in the circling area by studying the appropriate topographic map". The procedure designers use the best available information and factor in appropriate tolerances, but some of the topo maps that they have to work with are old and people can erect structures without notify them; the tolerances they use will, I believe, take into account allowances for things like mobile phone towers. So, don't rely on your RadAlt to keep you safe when circling, use your altimeter that's what they intend you to use.
Again, please read and understand what the minima table is telling you. These things are bloody important to know, not guess.
Sorry, end of lecture.
I respectfully suggest to you read and think about what is stated in the "IAL Legend" section of the Australian DAP's.
The height included next to the altimeter(ie pressure) minima is either, for an ILS, the height above the threshold, or for a non precision approach , the height above the aerodrome, at the minima.
You must not assume that this is the height above ground level immediately below you, for example the ILS at Nowra is an excellent example of how radio altimeter heights on a Cat 1(that's all we have in Oz) are absolutley not to be used as a minima/decision height. For those of you who are not familiar with Nowra, probably most non military pilots, the terrain at Nowra is such that the airfield is about 400ft AMSL located on a plateau; the approach flys up a valley and at the minima you have about 400-500ft on the RadAlt; seconds, and I mean seconds later, the aircraft will encounter rapidly rising ground as the valley ends and you cross the ridgeline, the ground then drops to the threshold.
If you where to attempt to use the RadAlt on this approach, which of course would mean disregarding the altimeter, and breaking more than a few rules and good airmanship, you would probably be very dead very quickly. It was suggested in the commissioning report of this particular ILS that there should be some notes included in the approach about this, but they were not.
There are a few other approaches in Oz where the terrain could lead you into trouble if you use RadAlt's incorrectly as well, eg Essendon.
With respect to non precision approaches, the second height stated is the height above the aerodrome. So, the terrain could do anything between the minima and the threshold. However, if you read the AIP ENR 1.5, 2.3 "Approach design concept", you'll find that the approaches are designed for a stabilsed decsent rate. The procedure designers do, I believe( I have talked to them previously regarding how they work things out) take into account the terrain clearances within the appropriate tolerances to the minima, to continue the approach to land you must be visual, so you avoid terrain with your eyeballs as the primary terrain clearance alert; circling approaches assume you will circle to land.
The RadAlt is of course a useful tool, if used correctly, as a cross check or crude terrain warning.
Another point well worth remembering is those paragraghs in AIP ENR 1.5 1.7.2 regarding "pilots should familiarise themselves with the location and altitude of obstacles in the circling area by studying the appropriate topographic map". The procedure designers use the best available information and factor in appropriate tolerances, but some of the topo maps that they have to work with are old and people can erect structures without notify them; the tolerances they use will, I believe, take into account allowances for things like mobile phone towers. So, don't rely on your RadAlt to keep you safe when circling, use your altimeter that's what they intend you to use.
Again, please read and understand what the minima table is telling you. These things are bloody important to know, not guess.
Sorry, end of lecture.
Last edited by Seaeagle109; 26th Jun 2003 at 08:12.
Thread Starter
Seaeagle109.
Thanks - I found the wording I was after in the Legend And your example of Nowra (never been there) is precisely the trap that I was outlining in my initial post.
My questions remain: why is that reference to RH made in the AIP 1.5.5.1.1? When would one use that? And where is the definition of RH?
which is why I asked the question. 
Thanks - I found the wording I was after in the Legend And your example of Nowra (never been there) is precisely the trap that I was outlining in my initial post.
My questions remain: why is that reference to RH made in the AIP 1.5.5.1.1? When would one use that? And where is the definition of RH?
These things are bloody important to know, not guess.
Stallie,
Sorry forgot to answer that bit.
If you look up AIP ENR 1.5-32 paras 8 & 9, Category 1 & 2 minima, you will find that only DA is mentioned for Cat 1 and Cat 2 mentions both DA & RH.
So, RH is only applicable for CAT 2 or higher.
As Arm out the Window says it's a wording to cover all ILS's; at a guess(sorry, shouldn't guess) it's there in case they decide to develope Cat 2 or better, or it maybe they've lifted it straight out of an ICAO document.
For your info, ILS's in Oz are calibrated to Cat 2 but are only actually capable for Cat 1 use due to other factors; YBBN 19 is an exception as it has the lighting requirements but not I am not sure why it isn't used to Cat 2, probably other things.
Hope this helps.
Sorry forgot to answer that bit.
If you look up AIP ENR 1.5-32 paras 8 & 9, Category 1 & 2 minima, you will find that only DA is mentioned for Cat 1 and Cat 2 mentions both DA & RH.
So, RH is only applicable for CAT 2 or higher.
As Arm out the Window says it's a wording to cover all ILS's; at a guess(sorry, shouldn't guess) it's there in case they decide to develope Cat 2 or better, or it maybe they've lifted it straight out of an ICAO document.
For your info, ILS's in Oz are calibrated to Cat 2 but are only actually capable for Cat 1 use due to other factors; YBBN 19 is an exception as it has the lighting requirements but not I am not sure why it isn't used to Cat 2, probably other things.
Hope this helps.
Thread Starter
Thanks for your replies - clears it up perfectly.
Still struggling to find the definition for "RH" though in the AIPs! We have all inferred the same meaning, but its odd its not there with the rest of them.
There is no interview BTW - just keep asking myself questions. Never had a radalt before so the thought never really crossed my mind. I am pretty content in employment at the moment! 
Still struggling to find the definition for "RH" though in the AIPs! We have all inferred the same meaning, but its odd its not there with the rest of them.
There is no interview BTW - just keep asking myself questions. Never had a radalt before so the thought never really crossed my mind. I am pretty content in employment at the moment!
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SE109,
With respect, the term should be "Cat 2 or lower", the presumption being the reduction in minima [Cat 3 being 'lower' than Cat 2.]
Hopefully, there'll one day be Low Visibilty approaches in Oz and then it will all become clear.
G'day
With respect, the term should be "Cat 2 or lower", the presumption being the reduction in minima [Cat 3 being 'lower' than Cat 2.]
Hopefully, there'll one day be Low Visibilty approaches in Oz and then it will all become clear.
G'day
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Feather#3,
IMHO I reckon Seaeagle is right, Cat 3 is a higher category than Cat 2 and Cat 2 than Cat 1 due to the requirements attached(lighting,site preparation,aircraft equipment,crew training,recency,etc) and an increase in those requirements as the minimas get lower; but I suppose it doesn't really matter does it.
IMHO I reckon Seaeagle is right, Cat 3 is a higher category than Cat 2 and Cat 2 than Cat 1 due to the requirements attached(lighting,site preparation,aircraft equipment,crew training,recency,etc) and an increase in those requirements as the minimas get lower; but I suppose it doesn't really matter does it.
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Looks like this issue has been pretty well resolved without me having to say anything. However, as I can't help meself, I'll just say that, in my dark little corner of the planet, we also refer to DA, MDA and RH. We agonised over the "RH" but decided to leave it there in case we ever adopt Cat 2 approaches.
I really don't see that happening here, but at least you now know the rationale. I'm guessing it's the same rationale in Oz. Ooops... I know... mustn't guess...
I was just fractionally troubled by this comment by Aotw though...
I trust that you only set this for circling. OCH in the final segment of a straight-in NPA can be as little as 250 feet.
I really don't see that happening here, but at least you now know the rationale. I'm guessing it's the same rationale in Oz. Ooops... I know... mustn't guess...
I was just fractionally troubled by this comment by Aotw though...
We used to set it at the appropriate obstacle clearance height on a non-precision approach, again as a guide, ie 400 ft for Cat B.
Ah, yeah, Oxexpat, I wrote that part a bit too quickly for my brain to catch up - yes, only setting 400 ft for circling; so be fractionally troubled no longer.
From Jeppesen AUSTRALIA-17
Differences from ICAO Standards and Procedures
DEFINITIONS
RADIO HEIGHT(RH) - The radio altimeter reading which is equivalent to the OCA adjusted for terrain/obstacle profile.
Differences from ICAO Standards and Procedures
DEFINITIONS
RADIO HEIGHT(RH) - The radio altimeter reading which is equivalent to the OCA adjusted for terrain/obstacle profile.
