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.

[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.

[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?]

My Two Bob's Worth

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

[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.