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MDA correction for area QNH

Old 17th Dec 2012, 14:25
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MDA correction for area QNH

Can anyone point me to the Jepp reference to this?
AIP DAP 1-3 states

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
.

(For info AIP GEN 3.5 para 16 lists those aerodromes that DO have a TAF available)

And if no reference is provided in Jepp does this mean that the 50 ft need not be applied as the Jepp forecast minima is the same as the DAP minima?
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Old 17th Dec 2012, 15:21
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Switched to Jeppview which doesn't keep the same format, however notes from way back when suggest it should be in Terminal, AU, Instrument Approach / Take off Procedures, Paragraph 5.3 (specifically 5.3.3). It was page AU-26 but this may have changed.

Same requirements apply, Jeppesen has just copied the Airservices data, but in their format.

Last edited by kalavo; 17th Dec 2012 at 15:27.
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Old 17th Dec 2012, 15:51
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Doesn't it tell you on each chart?
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Old 17th Dec 2012, 23:07
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compressor stall

I think you might be getting a little confused with TAF/TTF etc forecast and an aerodrome with no TAF. If forecast TAF with no AWIS/AWIB/ATIS/approvoved observer eg tower, then yes minima is on the charts and is typically 100ft above the lower minima with actual.

If no TAF and only have AREA forecast then 50ft added.
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Old 17th Dec 2012, 23:24
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Kalavo and HappyBandit.
Both of you allude to the same point as I have used so far , ie No TAF or actual QNH means use area and add 50 ft.

However I regularly go to places that do not have a TAF service as opposed to no TAF available. In this case AIP states that the adjustment need not be applied.
The Jepp ref 5.3.3 is the "add 50ft if using area" as per AIP.
What I am looking for in Jepps is the caveat as quoted in DAP.

Last edited by Agent86; 18th Dec 2012 at 00:43. Reason: Grammar and clarity
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Old 18th Dec 2012, 01:08
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VNAV_PTH,

What I am questioning is Airfields that have an approach but no regular TAF service.
The original quote from DAPS states that these plates already have this "adjustment" included in the minima so there is no requirement to add the 50 ft.

I can not find this caveat in Jepp but as the forecast/actual minima in Jepp are the same as in DAP for these airfields, I can see no reason to add the 50 ft.
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Old 18th Dec 2012, 03:15
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Slightly OT but can't AWIS/AWIB/ATIS/approved observer within 100NM be used for an accurate QNH?

AIP ENR 1.7-2 para 2.1.2 refers.

ie You don't need one on the field in question.

Last edited by Bograt; 18th Dec 2012 at 03:15.
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Old 18th Dec 2012, 03:32
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Bograt,
You can use that QNH for a local QNH. However for instrument approaches. AIP ENR 1.5 -33 para 5.3.1 (QNH sources) specifies

a. the actual aerodrome QNH from an approved source, or
b. the forecast Terminal QNH, or
c. the forecast area QNH.


No mention of local QNH so we are back to forecast area QNH as the only applicable QNH.
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Old 18th Dec 2012, 04:13
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Slightly OT but can't AWIS/AWIB/ATIS/approved observer within 100NM be used for an accurate QNH?

AIP ENR 1.7-2 para 2.1.2 refers.

ie You don't need one on the field in question.
I have noticed this idea becoming more common. The altimeter is the most important instrument for IFR and to use a QNH for an aerodrome 100 NM away is lunacy, especially if it is treated as an approved QNH for the purpose of reducing the MDA/DA.

Agent86 is completely correct.
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Old 18th Dec 2012, 04:48
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Agent 86, take a break for five minutes and have another read of it.

All approaches in Australia are designed as if you are using Forecast Terminal QNH.


If you have an actual QNH (ATC, ATIS, AWIS or CASA approved met observer and valid for 15 minutes) you can reduce the Forecast Terminal QNH minima by 100'.


If you do not have a TAF or TTF and hence no forecast Terminal QNH, you can use Area QNH, but you must increase the Forecast Terminal QNH minima by 50'.


It makes no difference whether your aerodrome has a regular TAF service or not. Though my understanding is BOM will provide a TAF on request for any aerodrome with an approach.

The only difference between DAPS and Jepps is the way they display the same data. Jepps likes to show the minima for Forecast and Actual QNH (but not Area), DAPS only shows Forecast. My guess is their reasoning is approach design varies a little worldwide, and they don't want people doing something dumb at 4am after a long overseas flight, because their country of origin's approaches are designed to actual QNH.




Edit:

Sorry reread your original question. You should find the places you are going to do not have the shading next to the minima on AIP charts. On Jepp charts they will only have one minima displayed. In both cases you should be adding 50' if using an Area. If this still doesnt make sense, let me know the aerodrome/chart and we'll try and pick apart the difference properly for you.

An example of where a regular TAF service is not AVAILABLE (different to provided) is Bromelton in Brisbane. ASA charts not shaded (can't reduce the minima), Jepp's only provides one minima.

Last edited by kalavo; 18th Dec 2012 at 05:07.
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Old 18th Dec 2012, 05:54
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Kavalo,
I have read and reread it. That's why I am asking the question.

Refer to YBRY
https://www.airservicesaustralia.com...RYGN03-133.pdf
The Jep chart also has actual and forecast minima. However there is no regular TAF service.

Again even if you get a special on request TAF the para in DAP I qouted means you do not add the 50 feet. There is no corresponding (that I can find) dap introduction notes 1.11 in Jepp. Now that is probably a Jepp translation error and not an error in the source AIP.
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Old 18th Dec 2012, 06:12
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Hmmmm, it appears this has changed recently (black mark next to the paragraph, meaning it's been changed in the latest ammendment).

What I used to believe was the case, was any approach you did using Area QNH (regardless of the weather services provided), you added 50ft to the minima that did NOT account for accurate QNH.

What it now appears to say, is if the aerodrome you are conducting the approach into, is NOT subject to any weather service (TAF, TTF, METAR, AWIS/B) at any time, then it assumes that you will always be conducting an approach using Area QNH, therefore the minima has been worked out based on that assertion.

BUT, if the aerodrome DOES receive a weather service (even if not full time), if you shoot an approach using the Area QNH, then throw another 50ft onto the minima that doesn't allow for an accurate QNH.

There, clear as mud, . And thank you for alerting me to this piece of useful information that has changed, .

morno
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Old 18th Dec 2012, 06:41
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Nice find, it is an inconsistency.

Obviously losing it in my old age and failing to RTFQ.

Your next step is probably...
https://www.airservicesaustralia.com...s/contact-form

They're generally more than happy to help, and given they're the primary publishers of the information can explain exactly what they mean, and speak to Jepps if Jepps don't have it (that we can find) or have it wrong.

Old copy of DAPS got binned so cant even look up a previous verison to see if it made more sense for you.
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Old 18th Dec 2012, 09:56
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@scavenger:

I have noticed this idea becoming more common. The altimeter is the most important instrument for IFR and to use a QNH for an aerodrome 100 NM away is lunacy, especially if it is treated as an approved QNH for the purpose of reducing the MDA/DA.
I was told this by the Head of Standards for a very reputable operator.

Last edited by Bograt; 18th Dec 2012 at 09:57.
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Old 18th Dec 2012, 10:47
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I was told this by the Head of Standards for a very reputable operator.
I would suggest that Head of Standards needs some further education.

The ICAO documents consider a remote altimeter setting source as being a source greater than 5nm from the intended landing aerodrome, up to a maximum of 75nm. There is an adjustment to MDA required of 5ft per NM greater than 5NM.

I would suggest that if you are using a remote setting source 100nm away then a 475ft correction needs to be applied to the minima. So this assertion that you can use setting sources great distances from aerodrome is plainly incorrect. Even a source 10nm away will need a correction of 25ft.

As to the questions regarding the use of Area QNH. As part of the procedure design process we are required to check if the aerodrome has a TAF service. If no TAF service available then we incorporate the extra 50ft into the published minima.

Alpha

Last edited by alphacentauri; 18th Dec 2012 at 11:12.
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Old 18th Dec 2012, 13:42
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AlphaCentauri
As to the questions regarding the use of Area QNH. As part of the procedure design process we are required to check if the aerodrome has a TAF service. If no TAF service available then we incorporate the extra 50ft into the published minima.
By "we" I assume you are talking ASA and that is what the DAP intro para 1.11 refers to.

Any chance of the "we" letting Jeppesen know so they can add that little note into their "interpretation" of the AIP/DAP.
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Old 18th Dec 2012, 14:07
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ATC AU-501
1.2 Altimeter Setting Rules
1.2.1.2 For ALL OPERATIONS at or below Transition alt (in the alt setting region), (see fig 1 pg AU 502), the alt reference will be:

a) the current Local QNH of a station along the route within 100nm of the a/c; or

b) the current Area Forecast QNH IF the current Local QNH is not known.

the above means on clb and desc.

AU-501
1.2.3. Local QNH
1.2.3.1. Local QNH, whether providedby ATS, AWS, or TAF or by using the alt subscale to indicate airfield elevation, is used as shown in figure 1. (AU 501)

In addition see MET AU-37, 4.3.1 & 4.3.5 (.......Therefore QNH from these AWSs may be used in accordance with TERMINAL INSTRUMENT APPROACH/TAKEOFF PROCDEDURES, QNH SOURCES.

Almost finally, see TERM AU-29, 5.3 QNH SOURCES, 5.3.1. Prior to passing the IAF, the 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

Using common sense, does anyone think that Area F/cast QNH is more valid than a "live" actual qnh from within 100nm and is no more than 15 mins old, when the Area F/cast Qnh within that area only has to be within 5mbs and covers how many sq kms, and some think 100nm is too far. ICAO reference to distance and qnh for Oz has nothing to do with us.

WALLY, there is no definition of 'actual' qnh in Jepps that I can find which is why is isn't in caps, other than a dictionary definition of actual (actual |ˈak ch oōəl|
adjective
1 existing in fact; typically as contrasted with what was intended, expected, or believed : the estimate was much less than the actual cost | those were his actual words.

That means real, live, not f/cast!
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Old 18th Dec 2012, 14:28
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Using QNH within 100nm

Some of you guys are getting this bit wrong. You may use an actual QNH within 100nm of you in lieu of the area QNH, BUT all of the area QNH limitations still apply. You can not use the 100nm QNH to reduce any minimas or to waive the requirement to add 50' to the forecast QNH approach minima (Agent86's discovery aside.)

Example: You are going to aerodrome A and although it has a TAF service, there is no TAF available for your arrival. Normally you'd be required to use the area QNH and add 50' to the forecast QNH minima. However, if the area QNH covers a large area, as many do, and there is an aerodrome "B" only 40 nm away that has an AWIS, you may use the aerodrome B's QNH in lieu of the area QNH. The chances are it will be more relevant to the aerodrome you are going to than the area QNH would be. BUT you must still add the 50' to the minima, it doesn't allow you to use the TAF QNH minima or the actual QNH minima.
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Old 18th Dec 2012, 23:12
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An actual QNH can only be from the spoken word:-)
Not if you get ATIS via ACARS and print it out
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Old 19th Dec 2012, 14:16
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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.
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