IREX help

[Nick1]

I am studying for the CASA IREX and have come across something that I can`t seem to get a definite answer for.

Jeppesen Terminal AU26 5.3.3 states "Where the forecast area QNH is used, the forecast Terminal QNH minima used must be increased by 50ft.

The way I read it is if you use area QNH then 50ft must be added to every minima MDA/H and ALTERNATE minima which would make sense for the inaccuracies of the AREA QNH and forecast.

But my teacher seems to believe that it is only to the MDA, and cant find anyone who knows. If it was for MDA it should state MDA but it doesn`t thats why I am lead to believe it is for all minimas including ALTERNATE.

If anyone has a definite answer to this please let me know.

Thanks.

[PPRuNeUser0163]

Nick1,

pretty sure (happy to be corrected if wrong) that if local qnh is not available you would add the 50ft onto mda/dh and the alternate minima.

Makes sense as if your charts are shaded (ASA) you can subtract the 100ft off the mda/dh and the same can be done for the alternate criteria.

[Nick1]

Well thats how I read it but my instructor/cfi/ato seems to think otherwise.

I just have the exam this week and this is the only thing he doesn`t agree with me on.

Thanks.

[The Green Goblin]

The alternate minima is just that, the alternate minima. You don't need to add anything to it at all. If you need to shoot an approach and you don't have QNH from an approved source then you add 50 feet to the minima.

Think of this practically, you are flying to Alice Springs you planned the flight with the usual considerations with alternates. You arrive outside tower hours and the AWIS is down. You use area QNH instead for your instrument approach and add 50 feet to the minima. You are not planning what approach you will fly when you get there in the planning stage, the consideration is the aids available and your currency using them. If the wx is below the alternate minima you have an alternate. If the conditions on your arrival are below the MDA/DA technically you can't even shoot the approach and you divert or hold if it were endorsed tempo/inter.

Keep it simple :)

[Lasiorhinus]

Terminal AU26 5.3.3 / AIP ENR 1.5 5.3.3
Where the forecast area QNH is used, the forecast Terminal QNH minima used must be increased by 50ft.

Minima is plural. Therefore you increase all the minima.

Read para 5.3.2 above it: "The published minima for DME or GPS arrival procedures, landing, circling and alternate minima have been calculated assuming the use of forecast terminal QNH"


I still don't understand why they publish alternate minima to the accuracy of one foot, but cloudbases are only forecast in hundreds of feet.

[ZappBrannigan]

I asked the same question a while back - if read carefully, the reg you posted says if forecast area QNH is used, then 50' must be added to the minima. Not area QNH, but forecast area QNH. When centre says "ABC, area QNH 1013", this isn't forecast area QNH, it's actual area QNH. So, I believe, nothing need be added to any minima.

Think of this practically, you are flying to Alice Springs you planned the flight with the usual considerations with alternates. You arrive outside tower hours and the AWIS is down. You use area QNH instead for your instrument approach and add 50 feet to the minimaI know you know your stuff GG, but I think this above is another example of where some get confused. If the AWIS is down, then you don't have an accurate local QNH, so you must use the forecast terminal figure on the Jepps. Assuming centre gave you the area QNH though (or you're using the forecast terminal QNH for AS), there's no requirement to add another 50'. We've already automatically added a 100' buffer due to not having the actual terminal QNH. The extra 50' buffer is if we're using forecast area QNH.

This is how I understand it, anyway - and never been pulled up on it during approach briefings on any test or renewal I've done.

[Hot High Heavy]

I feel your pain Nick1, i have the IREX this week too! :eek:

My understanding though was that it related to forecast QNH too, ie if you dont have actual then you add 50ft.

Good luck with the exam!

[Marauder]

Zapp said

"Not area QNH, but forecast area QNH. When centre says "ABC, area QNH 1013", this isn't forecast area QNH, it's actual area QNH."

Not Correct IMHFO, but this is a rumour and advise forum, so no knocking is intended, and my reply has the same caveats if anyone chooses to disagree.

I think that it is`fantastic that a`question can be asked an various answers and opinions appear. Look at the Norfolk fuel thread, some of the respondents have been around since Pontious the Pilot soloed in the Kitty Hawk and they still don't agree, it simply points out the ambiguity and deficiency in some of the rules regs etc

Area QNH is a forecast and covers a 3 hour period, it may be amended from time to time, but still is a forecast and should be accurate to with 5 hpa of a reporting station within the area also a forecast TAF in that area, hence sometimes an amendment. Because of localised variations sometimes the 5 hpa can not be maintained an then the area will be split. i.e Area 50 N of PLC-BOR 1023 S 1017. In particular in the Top End when tropical lows are present quite a multiple split is published.

:D

[Nick1]

Point taken I just jumped the gun.

So are we agreed that 50ft has to be added to all minima MDA/H and ALTERNATE to forecast area QNH, but not to actual area QNH??

[Marauder]

Nick

Area QNH by definition is Forecast

Refer Jepp Met AU-1

AREA QNH -A forecast QNH etc

[ZappBrannigan]

Not Correct IMHFO, but this is a rumour and advise forum, so no knocking is intended, and my reply has the same caveats if anyone chooses to disagree.

I think that it is`fantastic that a`question can be asked an various answers and opinions appear. Look at the Norfolk fuel thread, some of the respondents have been around since Pontious the Pilot soloed in the Kitty Hawk and they still don't agree, it simply points out the ambiguity and deficiency in some of the rules regs etc

Area QNH is a forecast and covers a 3 hour period, it may be amended from time to time, but still is a forecast and should be accurate to with 5 hpa of a reporting station within the area also a forecast TAF in that area, hence sometimes an amendment. Because of localised variations sometimes the 5 hpa can not be maintained an then the area will be split. i.e Area 50 N of PLC-BOR 1023 S 1017. In particular in the Top End when tropical lows are present quite a multiple split is published.Point taken. I still think, with regard to minima, that a distinction is made between the area QNH supplied by centre and the forecast QNH you get on your ARFOR when you print it out.

I've had it explained to me the way I explained it, and during countless approach briefings, including to ATOs on renewals etc. (as I'm sure most here have done as well), I've never applied the 50' tolerance, nor did I on my initial flight test when operating off either forecast aero QNH (i.e. off the TAF) or the area QNH supplied by centre.

As it was explained to me, there is already a 100' buffer to account for the TAF QNH or supplied area QNH being a "forecast", not an accurately observed QNH. The extra 50' is when using the "forecast to the forecast" if you like, i.e. the forecast area QNH on the ARFOR (which obviously has quite a long validity time and may be quite incorrect).

So yes, area QNH as supplied by centre is techincally a forecast, but does not require the addition of an extra 50' - as I understand it and apply it in practice. When supplied with an area QNH, I use the "forecast terminal QNH" minima on the Jepps - not this + 50'.

[MakeItHappenCaptain]

Aside point for practical application,

remember that when reducing the minima by 100' for actual QNH (ie from an APPROVED source), it is only valid for 15 minutes. If you spend 15min holding, shooting multiple approaches etc, you need to re-verify the QNH or revert to the higher minima.:ok:

[43Inches]

The area QNH provided by ATS en-route is just read from the same area forecast you recieve. It may have been ammended since you printed it but it is still a forecast.

You must add 50ft to your minima if using area as it may be up to 5hpa(150ft) different from the actual aerodrome QNH. The forecast aerodrome QNH must be within 3hpa(90ft) of actual. This is the reason for the minima adjustments.

The reason alternate minima are down to a few feet acuracy is because it is set at 500ft above the circling minima (except special alternate minima).

[Ando1Bar]

Let's consider the practical application of alternate minimas and you'll see why adding 50ft to the alternate minima is a moot point.

From my experience, each airport with an instrument approach has a TAF service available (I won't say every airport with an instrument approach, but practically I haven't come across one without a TAF service). The TAF will contain a valid forecast QNH for the airport across 12 hours. If the TAF is not available, or has ended when you plan to arrive, you must plan for an alternate anyway - therefore adding the 50ft is useless.

Over the last 18 months I had over 50 students sit and pass IREX, and none were pulled up for answering a questions about area QNH/alternate planning incorrectly. To the guys above who are sitting IREX soon, move on and study something more likely to come up in the exam. For example, make sure it is clear in your mind the differences between MDAs and alternate minimas, and what the figure actually means i.e. is the cloud base talking about height above aerodrome or mean sea level? This is much more likely to catch you out during an exam.

[OZBUSDRIVER]

Have you guys actually read the AIP?

ENR 5.3 QNH Sources

ENR 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.

ENR 5.3.2 Where instrument approach charts are identified by a shaded
background to either the minima titles for the IAL plates or the
published minima for DME or GPS arrival procedures, landing, circling
and alternate minima have been calculated assuming the use of
forcast terminal QNH. (thats a TAF) These minima may be reduced
by 100ft whenever an actual aerodrome QNH is set. Approved sources
of actual QNH are ATC, ATIS, AWIS and CASA-approved
meteorological observers. An aerodrome QNH obtained from an
approved source is valid for a period of 15 minutes from time of
receipt (Note METAR QNH does not meet this requirment.)

ENR 5.3.3 Where forecast area QNH (Thats an ARFOR) is used, the minima
used must be increased by 50ft.

So...if the approach chart is shaded then you can reduce by 100ft if you have an actual QNH...if you have a current TAF, then no change...if you only have an ARFOR then add 50 ft....the 100ft is only available for the shaded boxes of the IAP. All other IAP is worked on forcast terminal..so add 50ft if no TAF. LANDING, CIRCLING AND ALTERNATE minima....me still a student on this but unless I have read it wrong also...AIP says Landing Circling and ALternate..

The source of QNH? TWR then there is ATC and ATIS...if ATIS is ZULU then need an AWIS. If no ATC at aerodrome, no ATIS and no AWIS then it is forecast area...Enroute ATC? Do they have access to what is actually recorded at an aerodrome out of tower hours?

Think about where our En-route ATC are based...and ask how they can have access to ACTUAL area QNH. They use ARFOR, same as pilots.

[Nick1]

Thanks for all your comments guys.

I think i`m going to just go with adding the 50ft if using forecast area QNH.

Cheers :ok:

[43Inches]

When completing airlaw questions just read the law as written and apply it; as stated above the rule states that if using area QNH 50ft must be added to all minima.

12.17.3 Up to four forecast values of QNH are given, for the times HH,

HH+3 hours, HH+6 hours and HH+9 hours, where HH is the time
of commencement of the TAF validity period. These forecasts are
point forecasts for these times but are valid for: in the case of the
first value, ninety minutes after the time point HH; and, for
subsequent values, ninety minutes each side of the time point.
The QNH forecasts are prefixed by the letter “Q”.
Ando1bar;

If you were planning to a destination with a 12 hour forecast and planned to arrive 65 minutes before the TAF expired you would be outside the 90 minutes from the last QNH provided. Therefore the planned arrival would need to be on the forecast area QNH, add 50ft to alternate minima. You still have a valid forecast but not a valid QNH at arrival time. It is a very unlikely situation however it is remotely possible.

[ZappBrannigan]

Ok then, I retract some of my previous points. Fair enough, I'll accept there isn't any distinction between area QNH and "forecast" area QNH. There are a lot of people out there teaching otherwise.

It's also extremely common practice (correct or not) to conduct approaches on the area QNH supplied by centre, NOT on the forecast QNH found on the TAF. And from what people are saying now - this involves a 50' increase to MDA. I have flown and witnessed heaps of approaches, to or close to minima in IMC, on area QNH using the "forecast terminal QNH" figure on the plate, without adding 50'. An interesting legal point that I'd like to clear up.

[43Inches]

Zapp;

Airlaw is just like the rules of the road, you can do whatever you want and most of the time get away with it, much like speeding drivers. When something goes wrong you better hope your explanation of why property was damaged or persons injured conforms with the law. If not you may be paying off a debt for a long time, or worse. Most people who talk of grey areas in the law just don't like what it tells them to do so they claim ignorance to it.

[Ando1Bar]

Good thread guys. 43 and OZ, good comments - you've made me consider something I've never really had to think about before. Practically it is a very rare situation but as mentioned it could apply to those last 90 mins. Personally I've never added 50ft to alternate minima as I've always planned to arrive with plenty of validity remaining or was able to get an updated TAF.

As mentioned though, I haven't come across an IREX question requiring you to use area QNH when considering alternate minima.

It's also extremely common practice (correct or not) to conduct approaches on the area QNH supplied by centre, NOT on the forecast QNH found on the TAF. And from what people are saying now - this involves a 50' increase to MDA. I have flown and witnessed heaps of approaches, to or close to minima in IMC, on area QNH using the "forecast terminal QNH" figure on the plate, without adding 50'.

:=

[Nick1]

Again OZ and 43 well done, you confirm what I thought was right (and how I read the regs)

Dont think my instructor will be happy when I tell him he is wrong and refer him to this thread.

Thanks again guys.:ok:

[desmotronic]

Nick,
Before you give your instructor a hard time be aware that if you are going to get hung for something it will be a breach of the CAR's. CAR 257 as referred to by ENR 1.5.1 define your responsibilities in relation to landing and take off minima only, they dont mention alternates. In any exam i would expect questions on this subject to be relating to MDA/DA. Despite the way ENR 1.5.3.2 reads im not convinced it is intended to relate to alternate minima.

[The Green Goblin]

You'd be a twit to add 50 feet to the alternate minima considering you don't know the exact source you will be using until you are there, unless of course there is no TAF or AWIS at the aerodrome.

You need to ask yourself why is 50 feet added to the minima? It's added to keep you at a particular height above the ground allowing for errors in QNH in the event you are not visual at the MDA. The alternate minima is an exact measurement above the ground and the forecast cloud is AGL for an aerodrome or AMSL for an area forecast in the case that you are using LSALT + 500 for your alternate minima.

Just think about the intentions of adding the 50 feet!

Again OZ and 43 well done, you confirm what I thought was right (and how I read the regs)

Dont think my instructor will be happy when I tell him he is wrong and refer him to this thread.

Thanks again guys.

I think he will be giving you a look before failing you for your stupidity. You always need to look for the reason why a reg is written and the practical application.

Zappy, any time I'm using area QNH I'm going to add 50 feet the the MDA especially when I was bug smashing using the LSALT as my 'MDA' in IMC at a bush strip without a TAF/ATIS/AWIS.