MDA correction for area QNH
Ok "DD" (gee I hope yr not a sheila:-)
that's a fair comment although the source is still from the spoken word just written on bark with charcoal
'catS2A' that's good advice
Wmk2
that's a fair comment although the source is still from the spoken word just written on bark with charcoal'catS2A' that's good advice
Wmk2
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It is my understanding, from consultations with Jeppesen while trying to get an approach published somewhere else in the world, that they just re format an existing approach. They do no survey work them selves and rely on the originators calculations for safety (please correct this statement if not accurate) Therefore all requirements of DAPs in ENR 1.5 must be applied to assure the same level of safety. If these requirements can't be found in Jep pubs then this may be a problem? I believe a USAF 737 crash highlighted the risk of relying on Jep re formatted approaches with appropriate supporting documentation.
Rogan, that is essentially correct. Jeppesen take the data and reformat it. Almost all of the AIP is contained in the Jepp manual verbatim. The only real differences are where the paragraphs refer directly to the format of the charts.
The problem here is that the DAPs have been formatted such that the area QNH correction is not needed if there is no TAF service for the aerodrome. The reason being that the only possible QNH you may use is the area one and therefore there is only one minimum you can use.
Jeppesen have reproduced the same minima from the DAPs but because this little quirk is effectively associated with the formatting of the DAPs, Jepp don't seem to have picked up that those charts already have the area QNH correction applied. The result is that if you read and use the Jepps exclusively you will add a further 50' to the minimum when it appears that this isn't actually required as the Jepp minimum is a duplicate of the DAP minimum.
The problem here is that the DAPs have been formatted such that the area QNH correction is not needed if there is no TAF service for the aerodrome. The reason being that the only possible QNH you may use is the area one and therefore there is only one minimum you can use.
Jeppesen have reproduced the same minima from the DAPs but because this little quirk is effectively associated with the formatting of the DAPs, Jepp don't seem to have picked up that those charts already have the area QNH correction applied. The result is that if you read and use the Jepps exclusively you will add a further 50' to the minimum when it appears that this isn't actually required as the Jepp minimum is a duplicate of the DAP minimum.
Last edited by AerocatS2A; 19th Dec 2012 at 22:44.
Thread Starter
The interesting part will come next year when YBRY and YCWA get an AWIS but still no TAF service.
So you can use the Actual Minima (or take 100 ft if you use DAPs). However you should ALSO be able to take an additional 50 ft off as you are NOT using an area forecast.
For you boys/girls who fly to YFDF this should already apply!
Time for the Ops Support Departments to earn their money.
Alphacentauri, does my logic seem ... logical?
So you can use the Actual Minima (or take 100 ft if you use DAPs). However you should ALSO be able to take an additional 50 ft off as you are NOT using an area forecast.
For you boys/girls who fly to YFDF this should already apply!
Time for the Ops Support Departments to earn their money.
Alphacentauri, does my logic seem ... logical?
Alphacentauri, does my logic seem ... logical?
I would have thought that if the aerodrome had an AWIS/AWIB then surely its not a too far stretch of the imagination that a TAF service could be provided....but hey it seems some people forget that a certain corporate business name has the word "Services" in it.
To be honest, I think all this is a dogs breakfast, but I don't make the rules I just have to follow them
Last edited by alphacentauri; 20th Dec 2012 at 04:51.
The interesting part will come next year when YBRY and YCWA get an AWIS but still no TAF service.
I would have thought that if the aerodrome had an AWIS/AWIB then surely its not a too far stretch of the imagination that a TAF service could be provided
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WA - WAIT AWHILE.
Thread Starter
I have forwarded a request to ASA asking if we can expect a reduction in the minima of the approaches by 50 feet.
Let's see if the "design" team are in tune with the "law" team
Without these it's not much help.
Metar doesn't help much and with TSO129 the alternate Req is still there.
It is nice to see that the BOM is not just cut and pasting TAFs for YFDF,YBRY,YCWA. Today YFDF has TS (Prob) but YBRY des not.
Let's see if the "design" team are in tune with the "law" team
No details NOTAM wise about frequency or phone number to access
Metar doesn't help much and with TSO129 the alternate Req is still there.
It is nice to see that the BOM is not just cut and pasting TAFs for YFDF,YBRY,YCWA. Today YFDF has TS (Prob) but YBRY des not.
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Agent86,
What makes you think that the MDA for some approaches has the 50 foot correction "built in"?
Whilst it may seem logical for that to have happened - at those places served by neither a TAF nor an AWIS - it is also just as logical that this has not happened.
What makes you think that the MDA for some approaches has the 50 foot correction "built in"?
Whilst it may seem logical for that to have happened - at those places served by neither a TAF nor an AWIS - it is also just as logical that this has not happened.
Let's see if the "design" team are in tune with the "law" team
Probably bump the thread in another six months when left hand and right hand discover their mutual existence.
I have forwarded a request to ASA asking if we can expect a reduction in the minima of the approaches by 50 feet.
The other thing to consider is that the rule in the MOS requiring this extra 50ft has only been around since 2006. Prior to this it wasn't applied. If these approaches were published pre-MOS then I am sorry to say that there will be no expected 50ft drop in minima....but I will check it out for ya
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FYI, in NZ, if an aerodrome doesn't have a published QNH, then you use the nearest reported QNH, take the distance between the reported QNH and the aerodrome where you want to conduct an approach, subtract 5nm, then add 5ft for every mile remaining to the approach MDA.
Example:
Aerodrome A, with no published QNH, is 50Nm from controlled Aerodrome B.
50-5 = 45nm x 5ft = 225ft to add to the approach MDA for Aerodrome A whilst using the QNH from Aerodrome B .
Example:
Aerodrome A, with no published QNH, is 50Nm from controlled Aerodrome B.
50-5 = 45nm x 5ft = 225ft to add to the approach MDA for Aerodrome A whilst using the QNH from Aerodrome B .
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FGD, because the AIP says it has been built in.
Thanks AerocatS2A!
Well, that was a thoroughly dopey thing for them to do. Could you please give me an AIP reference on this. I am incredulous.
Well, that was a thoroughly dopey thing for them to do. Could you please give me an AIP reference on this. I am incredulous.
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If you have an aerodrome that doesn't have a TAF, ever, nor an AWIS, then there can only be one MDA so you may as well publish the MDA that everyone is required to use.
'Twould be better IMO to follow the rest of the world. One MDA and only one on each plate, always surveyed for accurate local QNH source. If you don't have a local QNH... refer to these rules regarding adding xxx feet.
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Try this
If there is no TAF, then the area QNH prevails.
Given that the area QNH is guaranteed to be within +/- 5 Mb, and at 30' per Mb, you then add 150' to the minima, unless your chart has a correction factor built in. Check for PANS-OPS.
If the area QNH is going to vary by more than5 Mb, then a speci would be issued.
QED?
Given that the area QNH is guaranteed to be within +/- 5 Mb, and at 30' per Mb, you then add 150' to the minima, unless your chart has a correction factor built in. Check for PANS-OPS.
If the area QNH is going to vary by more than5 Mb, then a speci would be issued.
QED?
Originally Posted by Oktas8
I beg to differ. It's that kind of thinking ("hey let's make it easy for the pilots by introducing an extra set of complexities into AIP") that has led to this two-page thread. What MDA shall I use if I have a privately-commissioned TAF? What if there's an airfield 8nm away with an ATIS, although this one has neither a TAF nor ATIS? What if this place has always had a TAF service, but last update BOM stopped providing the service?
'Twould be better IMO to follow the rest of the world. One MDA and only one on each plate, always surveyed for accurate local QNH source. If you don't have a local QNH... refer to these rules regarding adding xxx feet.
'Twould be better IMO to follow the rest of the world. One MDA and only one on each plate, always surveyed for accurate local QNH source. If you don't have a local QNH... refer to these rules regarding adding xxx feet.
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It's not that dopey. If you have an aerodrome that doesn't have a TAF, ever, nor an AWIS, then there can only be one MDA so you may as well publish the MDA that everyone is required to use.
1.
Let's say you are about to make an instrument approach to a place. Looking through the briefing material you printed before flight, you find that there is no TAF for the place.
So, you will be using the area QNH, but must you add on 50' to the published MDA or not? To answer that, you now need to delve into the Met section of the AIP (or check the ERSA entry) to find out whether the place has a TAF service or not. If not, then you don't add the 50'. If it does, then you do add the 50'.
2.So, you will be using the area QNH, but must you add on 50' to the published MDA or not? To answer that, you now need to delve into the Met section of the AIP (or check the ERSA entry) to find out whether the place has a TAF service or not. If not, then you don't add the 50'. If it does, then you do add the 50'.
If the IAL charts for a place have the 50' correction built in, then each time the TAF service status of the place changes, those charts must be amended and reissued.
Yes, I know that the TAF status for any one particular place doesn't change frequently, but over the course of a year, you may have one or two dozen places where the TAF status changes. That would then be one or two dozen lots of amendments to IAL charts that didn't need to happen.
Yes, I know that the TAF status for any one particular place doesn't change frequently, but over the course of a year, you may have one or two dozen places where the TAF status changes. That would then be one or two dozen lots of amendments to IAL charts that didn't need to happen.
The simplest approach, as others on this thread have alluded to, is to just have one published MDA, with no "built-in" corrections. That MDA could be the highest of the three possible, with the following corrections to be operationally applied:
1. Reduce MDA by 50' when the QNH is obtained from the TAF;
2. Reduce MDA by 150' when an actual aerodrome QNH has been obtained;
Alternative logic, that still keeps things as simple as possible, would be to have a published figure that assumes you have a TAF QNH. Then, if necessary, you:
1. Add 50' if using area QNH;
2. Reduce it by 100' if using an actual aerodrome QNH.