IFR QNH Source

[Jay Bo]

Hi all,

Can you use the for eg. Williamstown ATIS QNH as a QNH source for an approach into Maitland as an actual Aero QNH to use the lower MDA.

Cannot seem to find the rules either way except for the setting of the local QNH within 100nm of the aircraft.

cheers

[alphacentauri]

AIP ENR 1.5-33 details QNH sources as

a. Actual aerodrome QNH
b. Forecast Terminal QNH
c. Forcast Area QNH

As for distances I can find no reference in AIP for remote altimeter setting procedures. I do note that PANS-OPS allows the altimeter setting station to be up to 5nm away from the landing threshold before corrections need to be applied during the procedure design process.

Practically, I would say that if the altimeter setting source isn't at the aerodrome, then the altimeter setting is not valid to reduce MDA by 100ft.

Cheers,
Alpha

[Lasiorhinus]

Do you have the actual aerodrome QNH?

No.

Therefore you can't reduce by 100 feet.

[Wally Mk2]

Fair enuf question but there's a simple answer....NO

Agree with 'Las' here.


Wmk2

[Anthill]

I disagree, but I am willing to be corrected, the ATIS QNH is continually monitored and amended when appropriate by an approved observer. It is part of the continuous wx watch that is provided at these aerodromes. AWIB performs the same function regarding actual QNH. Thus, the lower, actual QNH minima can be used.

[belly tank]

Maitland has no awis, only info gained from Taf/area fcst

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 ATC, ATIS, AWIS and CASA-approved meteorological
observers. An actual aerodrome QNH obtained from an
approved source is valid for a period of 15 minutes from the time of
receipt (Note: METAR QNH does not meet this requirement).

[GreenerGrass]

If a nearby ATIS/AWIS QNH is permitted for the 100ft reduction it would be listed in the notes section on the instrument approach plate. eg West Sale.

[Wally Mk2]

'Anthill' what you say is correct but it doesn't apply to the posters original question, basically using another AD's QNH for a lower Min.

Only the spoken word is usable as a source for a QNH lower Min.

Wmk2

[desmotronic]

JB is this a compliance or safety question?

[MakeItHappenCaptain]

ATIS is valid for an area of 5NM around the aerodrome.
(Looking for a ref...)
If you're outside this (and Maitland is definitely so), no joy.

Serch for remote QNH in ur vols, in NZ its 5ft onto mda for every 1nm over 5nm from QNH Source

Thats us but i cant see it being too different in aus

Ignore this. Australia makes NO allowance for distance outside the ATIS area.:=
Love answers that have a good potential to confuse the issue by quoting a foreign rule.:rolleyes:

Jay Bo.
You may be getting confused with the preferred altimeter QNH setting when cruising below the transition altitude (10,000'). A known QNH from a source within 100NM is the first choice, followed by area QNH. ENR 1.7 Para 2.1.2 Don't forget area QNH is renewed every 3hrs if you are using it. :ok: