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MDA correction for area QNH

Old 19th Dec 2013, 04:31
  #41 (permalink)  
 
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Originally Posted by FGD135 View Post
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.
How often does an aerodrome change from TAF to No-TAF? If we're talking about superfluous amendments to the plates, then let's take a look at tomorrows Jeppesen revision cycle, 20 Dec 13. Remember that this is not even a revision date at all for the AIP DAP.


Adelaide One SID amended due to "initial climb text".
Albury DME arrivals (all of them) amended due to Cat C Minimums.
Albury Aerodrome chart amended due to changed alternate minima.
All the other Albury approaches amended due to changed circling minima.
Amberley aerodrome chart amended due to "note added".
Ballina aerodrome chart amended due to alternate minimums.
Coondewanna aerodrome chart amended due to "note added"
Hughenden (all plates) amended due to AWIB added.
Leinster aerodrome chart amended due to runway length.
Lismore RNAV 33 amended due to mandatory altitudes.
Mackay aerodrome chart amended due to parking bays.
Mansfield RNAV 115° amended due to MSA
Melbourne aerodrome chart amended due to Note Added
Moorabbin NDB-A amended due to missed approach training note
Mildura(all plates) amended due to AWIS removed, AWIB added.
Mt Gambier aerodrome chart amended due to takeoff minima, lighting
Naracoorte GPS Arrival amended due to MSA and profile depiction
Naracoorte RNAV and NDB amended due to MSA
Osborne Mine aerodrome chart amended due to RWY 30 lighting
Osborne Mine RNAV 30 amended due to PAPI added
Sunshine Coast aerodrome chart amended due to RNAV-X alternate minima
Sydney aerodrome chart amended due to parking bays renumbered
Sydney ILS-Z 16R CAT II amended due to RA added
Sydney ILS-Z PRM 16R CAT II amended due to RA added
Sydney ILS-Z 34L CAT II amended due to RA added
Sydney ILS-Z PRM 34L CAT II amended due to RA added
Sydney VOR 16R amended due to straight-in minima deleted, altitude table
Tennant Creek all plates amended due to AWIS added.

I'd say the occasional once or twice a year an airport changes landing minima to be pretty minor in the grand scheme of things.


Originally Posted by FGD135 View Post
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.
Perhaps I missed the sarcasm if there was any, but that is exactly how the current charts work. The published minima assumes you have a TAF QNH. If you are using Area QNH, then you do indeed raise the published minima by 50 feet. If you do have an actual aerodrome QNH, then you do indeed lower the published minima by 100 feet. That's what the shaded background indicates!
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Old 19th Dec 2013, 09:04
  #42 (permalink)  
 
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Perhaps I missed the sarcasm if there was any, but that is exactly how the current charts work.

No, that is not exactly how the current charts work - hence the existence of this thread.


If you're using area QNH for an instrument approach, you may or may not have to add 50' to the MDA. Refer my previous post.
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Old 19th Dec 2013, 10:58
  #43 (permalink)  
 
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My understanding was this.

If the airport normally gets a TAF, but for some reason on the day you go it isn't available, then you must add 50'.

If the airport never normally gets a TAF, then you would have to use the area QNH anyway and as a result you don't need to add 50'.
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Old 19th Dec 2013, 10:59
  #44 (permalink)  
 
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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: ...
Point taken FGD. As you say, that would be simpler than the current.

However, I'm a very simple guy. I want a system that defaults to the experience of most pilots, most of the time. And that, of course, is ATIS or equivalent. (Not to forget pilots operating at remote and/or poorly equipped airfields. But take the total number of instrument approaches flown each year in Australia: much more than half are to airfields with approved QNH sources.)

Hence my wish that the default scenario is for an accurate local QNH. When I'm flying somewhere without local QNH (as all do sometimes and some do all the time) I know I have to apply an MDA correction.

If you need local knowledge to interpret the plate MDA correctly, it's less safe than it could be.
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Old 19th Dec 2013, 11:20
  #45 (permalink)  
 
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If you need local knowledge to interpret the plate MDA correctly, it's less safe than it could be.
If you need local knowledge to increase the MDA, it's less safe than it could be.
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Old 19th Dec 2013, 15:28
  #46 (permalink)  
 
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Originally Posted by FDG135
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'.
Where's your reference for this? ENR 1.5 5.3.3 merely says:
Where the forecast area QNH is used, the minima used must be increased by 50FT.
No mention of the status of the aerodrome regarding a TAF service.
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Old 19th Dec 2013, 18:36
  #47 (permalink)  
 
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Meanwhile, in Australia, we have 3 pages devoted to a topic that is supposed to be clear, simple and unambiguous!
Well done Australia, if we can't go to the moon, let's at least make everything else a shot at it.

Bzbbzzbbzbzbzbzbzbzzzzzzzz
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Old 19th Dec 2013, 20:34
  #48 (permalink)  
 
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If you need local knowledge to increase the MDA, it's less safe than it could be.
That would be the current system Bloggs. The one where I arrive over an airfield with TAF QNH and wonder whether the place usually has a regular TAF service or not. What is the plate MDA based on? Head scratching. (Of course, local pilots would know.)

Last edited by Oktas8; 19th Dec 2013 at 22:05. Reason: Snark removed...
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Old 20th Dec 2013, 00:24
  #49 (permalink)  
 
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Where's your reference for this? ENR 1.5 5.3.3 merely says: ...
Bloggsy, please take a look at the first post of this thread (by Agent86). It gives those references and asks the very good question about whether AIP differs from JEPPs with regard to the addition of the 50'.
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Old 20th Dec 2013, 00:38
  #50 (permalink)  
 
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Yeh sorry FGD. One to you. Don't worry, I'll get ya next time!!

What MDA is Father Christmas going to use when he pulls into West Angelas next week on his Cat 3 C RNP AR WAAS night approach and landing??

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Old 16th Jan 2014, 00:20
  #51 (permalink)  
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Notam out for YBRY and YCWA

AIP DEP AND APCH (DAP) WEST YBRY AMD
TO ALIGN WITH DAP 1-1 GENERAL INFORMATION PARA 1.11, THE INTRODUCTION
OF THE NEW REGULAR TAF SERVICE ALLOWS THE PUBLISHED MINIMA TO BE 50FT
LOWER. WHEN THIS TAF SERVICE IS NOT AVAILABLE THE MINIMA MUST BE
INCREASED BY 50FT IN ACCORDANCE WITH AIP ENR 1.5 PARA 5.3.3.
NEW MINIMA IS AS FOLLOWS:
RNAV-Z(GNSS) RWY 10 S-I GNSS MINIMA 2950(894-5.0)
RNAV-Z(GNSS) RWY 28 S-I GNSS MINIMA 2700(644-3.7)
CIRCLING CAT A/B 3080(998-2.4) ALTERNATE CAT A/B (1498-4.4)
CIRCLING CAT C 3240(1158-4.0) ALTERNATE CAT C (1658-6.0)
FROM 01 100132 TO 04 100500 EST
The system works. Now for those of you who go to YFDF you had better go ask the same question of Airservices.
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Old 18th Jan 2014, 22:52
  #52 (permalink)  
 
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Originally Posted by Octas8
That would be the current system Bloggs. The one where I arrive over an airfield with TAF QNH and wonder whether the place usually has a regular TAF service or not. What is the plate MDA based on? Head scratching. (Of course, local pilots would know.)
How would you have a TAF QNH for somewhere that doesn't get a TAF?

I'd suggest that local knowledge isn't a major factor. When you plan your flight you will request a TAF from NAIPS and when it doesn't give you one you will investigate why.

The worst that will happen is you won't investigate and just assume the place normally has a TAF but doesn't today. You will get there, use area QNH or AWIS QNH from somewhere within 100NM and you will add 50' when you didn't have to.
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Old 19th Jan 2014, 03:07
  #53 (permalink)  
 
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You will get there, use area QNH or AWIS QNH from somewhere within 100NM and you will add 50' when you didn't have to.
My bolding...


Was mentioned previously but obviously some people haven't been picking up on it or are being told incorrect things (not having a go AS2A, I just want to point it out again as I still hear lots of people getting this thing mixed up), but for an Instrument Approach you cannot use QNH from a place within 100nm; doing this is for all other operations is an altimeter setting rule. The Application of Aerodrome Meteorological Minima section "supersedes" this:


ENR 1.5-5.3.1
Prior to passing the IAF, pilots are required to set either:
a) the actual aerodrome QNH from an approved source, or
b) the forecast Terminal QNH, or
c) the forecast area QNH.


Absolutely ZERO mention of QNH from within 100nm for your approach.


Is it likely to kill you? No, but it isn't the correct way to fly the approach.
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Old 19th Jan 2014, 03:50
  #54 (permalink)  
 
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Aerocat, in my example I was thinking of a place which has not had a regular TAF, but now has one issued. It happens occasionally.

Usually, if you have a TAF, there is no ambiguity. As FGD pointed out above (post 41), a more common problem is when NAIPS cannot provide a TAF for YXXX and you must decide whether that is a one-off or a regular thing. As a commercial pilot, I'm not interested in adding 50' to an MDA without strict necessity.

At the risk of being repetitive, I think a good system is one that defaults to the correct option for most users, most of the time. That would be an MDA based on an accurate local QNH. (I wonder why Jeppesen charts provide exactly that as the primary or default option? Hmm.)

Cheers, O8
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Old 24th Apr 2017, 06:02
  #55 (permalink)  
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Reviving an old thread.
The 2 Mar 2017 revision to AIP has removed Para 1.11 which started this off:
DAP-Reference

1.11 -AIP ENR 1.5 para 5.3.3 advises that "Where the forecast area QNH is used, the minima used must be increased by 50FT".
All ASA instrument approach procedures include this adjustment where a regular TAF service is not available(AIP GEN 3.5 para 16). No adjustment is necessary to meet the requirement of AIP for those aerodromes.
When an aerodrome receives a regular TAF service and the TAF is not available the AlP paragraph is applicable.
There is a subtle change bar with a D.

I asked ASA about this and they advised that CASA had requested that charts in the DAP (and hence Jeppesen) Effective 2 MAR 2017 don't include an extra 50ft in accordance with AIP ENR 1.5 par 5.3.4.

However ...the charts in question at any port that does not receive a TAF have not been revised to remove the 50ft
So in accordance the aforementioned AIP Enroute ref we have to add 50ft to the published minima even though the data already includes it!

I was advised that "cyclical maintenance" would reduce the minima ...so expect another raft of revisions. Until then we are much safer being that much higher above the hard bits

Just catching up with Worlds Best Practice I guess.

Last edited by Agent86; 24th Apr 2017 at 06:09. Reason: Added Ref to AIP
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Old 24th Apr 2017, 06:07
  #56 (permalink)  
 
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...so expect another raft of revisions
More inconvenienced electrons!
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Old 25th Apr 2017, 00:56
  #57 (permalink)  
 
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Um, its already been done. We took the 50ft off where it was applied at all locations over 12 months ago.
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Old 9th Apr 2019, 01:23
  #58 (permalink)  
 
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Just been reading this post before my IPC and noticed that “Forecast QNH” is written, opposed to area QNH assuming within the 15 minutes. So would argue that adding 50 ft is not required with a valid area QNH.
What do you guys think?
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Old 9th Apr 2019, 01:53
  #59 (permalink)  
 
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WHAT is an IPC?? Do you mean Instrument Rating Renewal?? Speak Strine will ya?!

that “Forecast QNH” is written, opposed to area QNH assuming within the 15 minutes.
??
Neither the (Aerodrome) Forecast QNH or Area QNH have anything to do with the 15 minutes.

If you are using the Area QNH (there's no such thing as an "actual" area QNH) you have to add 50ft to the shaded MDA (DAP) or the Jepp "Forecast Terminal QNH" MDA. AIP ENR 1.5 section 5.3.4 refers. I will not even attempt to find the ref in the useless Jepp Airway Manual.

If you are using an Aerodrome Forecast QNH ie from a TAF, you don't need to add the 50ft. Just use the shaded MDA (DAP) or the "forecast Terminal QNH" (Jepp). AIP ENR 5.3.2 refers.
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Old 9th Apr 2019, 12:04
  #60 (permalink)  
 
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Come on Bloggs, keep up, an IPC is strine, we have a world leading licence system now, Part 61 and all, no radio licence to show off overseas...

https://www.casa.gov.au/standard-pag...iciency-checks
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