ILS at an MBZ

[downwind]

guys,

when flying an ILS at an MBZ or non controlled airport and you have no AWIS/AWIB or actual QNH and the tower has gone home what QNH do you use to fly an ILS? assume you have got a current TAF

thank you,

DW.:confused:

[The Messiah]

The applicable one from the TAF the same as doing a NON-precision approach at an MBZ.

[downwind]

messiah,

the ILS plates don't have f'cast qnh they only have 1 qnh value, except if you are doing a llz app or a circling app off the ils/llz.

[Zhaadum]

Excellent question! Not too many MBZ with ILS around. Maybe if you add 100 ft to the DA (after PEC) you should be ok, and still lower than circling or LLZ minima. Can anyone confirm?

[Transition Layer]

Not too many MBZ with ILS around.

Actually there is a few but generally they are active during the day and MBZs at night (eg Canberra), or for the RAAFies (eg Willy, Nowra, Richmond), whenever they feel like making it active! Albany in WA is the only one I can think of which is a "proper" MBZ with an ILS. I cant be bothered going through the Jepps, but I reckon almost all of the RAAF fields have an AWIS in place outside of TWR hours.

Just remember the OM check height might be a fair bit off - but hey presto, there is your "explainable discrepancy" but depends on how you interpret the regs.

TL[

[Zhaadum]

Sorry TL, thats what I meant , a dinkum MBZ 24/7. :ok:

[maxgrad]

awib broadcast on VOR is seen as real time data, can use to reduce by 100', add PEC error though
AWS/AWIB will have information ZULU

[downwind]

gents,

the q refers more to fields such as TW,HB and LT when the TWR goes home there is no AWIB built into the VOR station ,you can only get the AWIB via phone line or mobile, not always the most practical way to get the AWIB, so what do you do???

[The Messiah]

Are you using Jepps?

[apache]

You could try getting a TTF METAR from AERIS or VOLMET. provided that is within the previous 15 minutes, then it is current.

ALSO... provided once again that it is within the previous 15mins, then maybe a METAR from Flightwatch WHERE it is AN AUTOMET / AWS , but given to you by FS, may be applicable ?

(Haven't got my Jepps with me, so can't give accurate answer re the METAR.)

[EngineOut]

apache,

you can't use METARs for actual QNH on approaches, even if it is less than 15 mins old. Don't have the ref handy, but remember being asked that in a proficeincy check once.

[downwind]

yes I am using jepps

[QSK?]

downwind:

Ref YABA R14 ILS and AIP ENR 1.5-30 para 5.3.

1. The published DA for the Albany R14 ILS is 480ft (530ft with PEC) which assumes an actual (valid) QNH is available.

2. AIP also indicates that, if an actual QNH is available, published MDAs in the shaded boxes may be reduced by 100ft.

3. Reverse logic would apply (I should think) if an actual QNH was not available ie the DA for R14 S-I ILS would now be 580ft (or 630ft with PEC) if using TAF QNH or 630ft (or 680ft with PEC) if using the Area QNH (para 5.3.3 refers).

This is only my interpretation but, I have to agree, nothing in the book that says my interpretation is correct. Very good question and one that I would like to see an official answer to.

Apart from the Unicom service at Albany, is there an AWIB service at all? What do Skywest (or other operators) do during daylight hours if Unicom is unmanned?

[swh]

Ask ML CEN on 123.9, ABA has AWIB available on 08 9842 1623 which is an approved QNH source.

[hoss]

From another angle, Jepp terminal AU-26 (5.3 QNH sources).

Have a look at the last paragraph 5.3.3 ......Where the forecast area QNH is used the forecast Terminal QNH minima used must be increased by 50 ft.

So how about using the area QNH which will be given to you by FIA and adjusting the minima.

The DA at TMW is 1640. Now that is based on an actual QNH so converting that to forecast QNH the DA is now 1740 plus another 50' because you decided to use area QNH makes the DA 1790.

Stuff that in your pipes and smoke it:) .

[Victor India]

My thoughts are that there is never (a legal requirement for) any adjustment to be made to an ILS minima regardless of the QNH source used, except maybe when an area QNH is used (AIP ENR 1.5 para 5.3.3).

I'm assuming this because there is never any shading associated with an ILS minima on an Airservices approach chart.

AIP ENR 1.5 para 5.3.2 mentions that those minima which have shading are based on forecast QNH which may be lowered by 100' if accurate QNH is available. Does this imply that those without shading (all ILS approaches) are based on accurate QNH?

I have a feeling that this may be an oversight since ILS installations are typically used at controlled aerodromes with accurate QNH sources. Also, the old check height rule of adding the difference if you're indicating high would keep you safe (even though it was intended to compensate for temperature error not QNH error). What if you went through 200' high under today's "unexplained discrepancy" rule? (See ENR 1.5 para 7.3.1.)

This is a little scary I guess since with a 200' DA, a QNH error (on the high side) of just 7hPa (equivilent to 210') would have you fly straight into the 1000' markers (or thereabouts) if you hadn't got visual first. In this case the OM check height would have been cause for alarm, showing you as about 210' high. I guess despite the new rule, no harm in applying the old one (since it's more limiting).

Why did they change the rule I wonder?

VI :ooh:

[jetblues]

Say you are flying into CB after the tower is closed and the airspace is now an MBZ. The cloud is broken at 1300ft so you are not going to get in off the VOR Rwy 17.

Next choice ILS-Y Rwy 35 DA2100 (230). There are certainly no comments on the Jepp charts to suggest you adjust the DA by 100ft for a forecast QNH. Remember you are using AWIS as the ATIS is inop (tower has closed).

Suggests to me you use the standard ILS minina. Damned good question though.

The question I ask is should RPT jets be regularly flying into non-controlled airports with high terrain and fly precision approaches ?

I NEVER enjoy it.

[hoss]

Have another read at Jepp Terminal AU-26 (5.3 QNH sources).

Theres your answer:) .

[jetblues]

Jepp AU-26 5.3.2 states "Approved sources of actual QNH are ATC, ATIS, AWIS and CASA approved met observers."

Canberra has an AWIS ( = actual QNH from an approved source), so no correction required for the ILS DA.

[tinpis]

One thing tin found when working in the UK was distinct lack of all this bull****.
If the weather and terrain was ever bad in Oz there be planes goin in like lawn darts.

[Victor India]

What about the case where you're flying an ILS but there is no source of accurate QNH? ie no tower and no AWIS? Rules don't say anything about adding to the minima if you're using forecast TAF QNH.....

VI

[QSK?]

Where's bl**dy OzExpat when you really need him?

[hoss]

C'mon fella's its really not that difficult.

QNH sources: "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.

So, inorder to answer Capt. downwinds original question. Lets say Captain downwind decides to use option c. forecast area QNH ( forget all the approved source bullsh.t, thats another topic).

Looking further into this back in 2.6 Aerodrome Operating Minima and 2.7 Instrument Landing System, nowhere does it mention using an actual aerodrome QNH (although probably the safest option).

So if Captain downwind arrives at TMW on a dark and stormy night and the ATIS and AWIS are 'NOTAMed out', whats to stop him or her;) from applying option c..

ie. TMW ILS Rwy 30R DA(H) 1640' (based on actual QNH) + 100' = 1740' + 50' (because Captain downwind was single pilot and busy and didn't have the opportunity to check the TAF or anything else while handling the engine fire) = 1790' DA.

Dont get me wrong not the best or smartest thing to do but whats stopping the application of this method from a legal and literal point of view.

Totally stand to be corrected, hoss:)

[Victor India]

Hoss (and others),

I have re-read the relevant sections in AIP, namely:

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.

and

ENR 1.5 5.3.2

"Where instrument approach charts are identified by a shaded background to either the minima titles for IAL plates or the published minima for DME or GPS arrival procedures, landing, circling and alternate minima have been calculated assuming the use of forecast terminal QNH. These minima may be reduced by 100FT whenever an actual aerodrome QNH is set. Approved sources of actual QNH are....."

In 5.3.2, it only mentions that shaded minima are based on forecast terminal QNH (and can be lowered by 100FT if an actual accurate terminal QNH is available). I initially assumed the same as I think you are assuming - that this statement implies that an unshaded minima is based on an accurate aerodrome QNH. It would then make sense to add 100FT if using a forecast terminal QNH.

In principle, I still feel this is by far the safest course of action. Still curious about what the officially correct method is, I called Airservices Australia today and the chap I spoke to reckons our assumption (that an unshaded minima is based on accurate QNH and therefore we should add 100FT if using forecast terminal QNH) is incorrect.

His advice is that regardless of the QNH source (unless using forecast area QNH where we add 50FT), the ILS can be flown to the published minima (plus PEC if required by the aircraft type).

I personally would feel very uncomfortable flying an ILS to the minima on forecast terminal QNH if weather was anywhere near the minima.

Whatdyareckon? :bored:

[OzExpat]

I've deliberately been staying out of this discussion, QSK, because it relates to Australian procedures and I haven't been keeping myself up to date on them. It's a bit simpler in PNG because we apply a shaded border to all Pans Ops 86 charts. We also say that this shading denotes that the DA or MDA has been calculated on the basis of forecast QNH.

Therefore, no matter what sort of approach it is, if you have an "actual" QNH, you can reduce the DA/MDA by 100 feet. Of course, for precision procedures, we also require pilots to make an appropriate adjustment for PEC (if required).

[hoss]

Victor India,

You said, 'Whatdyareckon' :ok: .

I say, 'ireckonAsAbettergettheirsh!ttogether'.

Jepp ATC AU-501 1.2.2 Area QNH.........'area QNH forecasts are to be within +/- 5 hPa of actual QNH at any low-level point:ooh: '........

Wow, i'd feel really 'bummed out' if i applied the ASA technique flying into Launy, Hobart or Albany to mention a few and only applied a 50 ft adjustment to the DA.

Thats if I had to use option C. (last resort).

A bit ironic that 5 hPa equates to roughly 150 ft though:ok: .

hoss:)

[QSK?]

OzExpat: I've deliberately been staying out of this discussion QSK.....OzExpat, mate, my previous post was calling for your participation in this subject only because of the high respect I hold for your knowledge and opinions on all things relating to PANS-OPS.

Distilling the comments in your last post, as well as the posts from others, I would appear that CASA/ASA may need to also consider publishing (certainly for those ILS approaches in non-controlled airspace) a DA based on forecast QNH and then also shading the box to indicate to the pilot that the DA can be lowered by 100ft if an actual QNH is available (+ PEC of course). Is that how it works in PNG?

[Victor India]

Hoss and others,

Just had a call returned from my contact at CASA. This topic appears to have drawn attention there and he informed me that some change to the rules will be made in upcoming amendments. What form that will take is as yet undetermined.

This will only affect the unique case where an ILS is being flown to an airfield with no accurate QNH available (eg tower gone home and AWIS broken).

I've recently been looking also at the positon of the Middle Marker. It is almost always near as dammit coincident with the ILS MAPT (defined as the intersection of the electronic glideslope and the Decision Altitude). For a long time I've been in the habit of deselecting the marker button once the Outer Marker check is comlpete to avoid the annoyance of the MM right on the minima. Seems it would be safer to listen for it as another cue that the MAPT has been reached.

VI:ok:

[botero]

Victor India is correct when stating that the ILS MAPT is coincident with the MM (or a DME fix when no MM is possible eg. an over water approach).

The ILS is designed to fly the pilot to a set point in space (a set distance out at a set true altitude on the published glideslope typically 3 degress) and its published minima are then predicated on 2 things from this point:

1) what airfield lights are available etc (so you end up with 800m vis requirement or 1500m etc)

2) what the MAP obstacle clearance path needs to achieve 2.5% (traditionally about 200' AGL but can be a lot higher such as at CB)

As this point is defined by a DME fix and/or a MM it stops the aircraft from being flown through the designed safe point.

As pilots we fly it reference to altimeter height and it is set by order of accuracy available to us - accurate then TAF then AREA.
So in the question we should set TAF QNH then fly to published minima. The OM/DME check height will give you an altimeter glide slope relationship check.

Now at the OM IF:

1) you were on glideslope and were low on idicated (altimeter) height you will strike the DA prior to the designed MAPT (actually on correct glideslope but physically further up the slope so true altitude is higher).

2) you were on glideslope and were high on idicated height you will strike the MAPT prior to the DA as you will have an actual lower true altitude.

So in effect the MAPT is not purely predicated on reaching the DA, rather it is what you reach first, the DA or the MAPT. In effect then the QNH you set will simply give you a more realistic appreciation of where on the glideslope you are and better your chances of arriving at the designed MAPT at the optimum altitude, not getting stuck further up the slope and lessening your chances of getting in.

ASA have given VI correct advice in that you will only add 50' to ILS minima if using AREA QNH as this is what is built into the design criteria of the ILS. For the same reasoning above you can not reduce an ILS DA with accurate QNH as it will put you through the MAPT.

Now it is time for me to don flak jackets, get into bunker and await the incoming barrage of fire!!!

[OzExpat]

G'day QSK, thanks for the compliment, but I'm not sure that I have anything like all the answers from Pans Ops.

I haven't had any opportunity to keep up with the Oz rules because of the problems that have emerged since PNG issued it's new Civil Aviation Rules in January last year. So many problems that I haven't had any capacity to recapture the Oz rules. My Oz CIR expired about 2 years ago and I'm planning to get it back later this year, so will have to get back up to speed then. :uhoh:

I've had a long-standing difference of opinion with CASA on the whole subject of minima declaration. Yes, all our Pans Ops 86 charts allow a 100 feet reduction of DA or MDA if actual QNH is available. I've always thought that this was the safer way to do it because it errs on the safe side - if the pilot forgets about the advantage of the actual QNH, there is no adverse effect on safety.

It's been working pretty well here for quite a few years now, but CASA hasn't seen fit to follow this method. I believe that it's a lot simpler for pilots and certainly doesn't complicate matters for me as the procedure designer. :ok:

botero... no flak from me! I'd been waiting for you to make the point about the under-reading/over-reading altimeter situation, so that folks don't use the MM (or DME fix) as their new God. You did that and I think you made the points well - the sort of thing that was always part of my questionning of candidates for a CIR.

I'm not so sure about AsA's justification for the 50 feet increase though. I've been following this topic since it started and think that there's clear evidence that CASA has over-complicated this situation.

[Victor India]

It's been a while since the last post on this thread, but I have just noticed that there is now shading on the ILS minima on the Airservices Australia DAP plates for those aerodromes which deactivate and accurate aerodrome QNH may be unavailable (I'm a bit slow seeing this... sorry I haven't been to these places for a while).

Here's the Tamworth ILS plate as an example:

http://www.airservices.gov.au/publications/current/dap/STWII01-105.pdf

Seems CASA may have responded to the concerns and suggestions aired here on Pprune. How about that?

[Brian Abraham]

Approved sources of actual QNH are ATC, ATIS, AWIS and CASA approved met observers

Question. You are flying into a place where the AWIS is only available by phone. Is it legal for a third party such as a company employee to obtain the info and pass to you by radio so that you can reduce the minima by the 100 feet. Ops manual does not address the issue. My take is no but would appreciate other opinions.

[Victor India]

I believe the AIP only stipulates that an actual QNH is valid for 15 minutes. How that information flows to the crew is a company matter.

Some companies require that both (or all) pilots independently confirm the QNH from ATIS or whatever.

Is it any different a copilot copying down an ATIS and the crew using that for the approach, compared to a company agent on the ground copying it down and passing it by radio to the aircraft? I'd suggest that both are legal as per AIP, yet both are quite susceptible to human error. It comes down to how well you trust your company rep, how good your comms are, etc.

I think this procedure in combination with a healthy awareness of the forecast QNH (as a gross error check) is probably ok. I'm sure many others will disagree...

:)