Altimeter Question

Stefan <stefan@mus._INVALID_.ch> wrote in news:c9458$4807bcae$54487328$4551
@news.hispeed.ch:

> WingFlaps schrieb:
>
>> Perhap we are at crossed purposes but an ARFOR does not refer to an
>> airfield -that's a METAR and not all fields issue them. So in this
>> case how can QNH give field elevation unless it's an ISA day?
>
> Again: QNH gives *by definition* the field elevation.

Only at the airport ref point, so, no, it doesn't.


Bertie

terry <tfmann@iprimus.com.au> wrote in news:375462b0-66e7-4ed0-b45d-
e6e089f79270@s50g2000hsb..com:

> On Apr 18, 7:10 am, Stefan <stefan@mus._INVALID_.ch> wrote:
>> WingFlaps schrieb:
>>
>> > Perhap we are at crossed purposes but an ARFOR does not refer to an
>> > airfield -that's a METAR and not all fields issue them. So in this
>> > case how can QNH give field elevation unless it's an ISA day?
>>
>> Again: QNH gives *by definition* the field elevation. If an ARFOR
gives
>> you a QNH, then it is related to one well defined spot on the
surface.
>
>
> As I understand it ( In Australia) the QNH in an ARFOR must be within
> 5 mbar of the "real QNH" - ie what gives you field elevation for any
> place within that area. otherwise the area will be broken up into sub
> areas and no 2 adjacant sub areas must differ by more than 5 mbar.
> That way the errors which Wing flap alludes to, and must certainly
> exist in non ISA atmosphere, would result in errors of no more than
> 150 feet between aircraft using either the correct AFROR QNH or the
> airfield set QNH
>
>
>

Yipes! Are you studying to be an astronaut?

Bertie

On Apr 18, 9:10 am, Stefan <stefan@mus._INVALID_.ch> wrote:
> WingFlaps schrieb:
>
> > Perhap we are at crossed purposes but an ARFOR does not refer to an
> > airfield -that's a METAR and not all fields issue them. So in this
> > case how can QNH give field elevation unless it's an ISA day?
>
> Again: QNH gives *by definition* the field elevation. If an ARFOR gives
> you a QNH, then it is related to one well defined spot on the surface.

BINGO! That's right, setting QNH on an altimeter DOES NOT does give
field elevation UNLESS it's issued for that field :-)

Cheers

On Apr 18, 10:02 am, terry <tfm...@iprimus.com.au> wrote:
> On Apr 18, 7:10 am, Stefan <stefan@mus._INVALID_.ch> wrote:
>
> > WingFlaps schrieb:
>
> > > Perhap we are at crossed purposes but an ARFOR does not refer to an
> > > airfield -that's a METAR and not all fields issue them. So in this
> > > case how can QNH give field elevation unless it's an ISA day?
>
> > Again: QNH gives *by definition* the field elevation. If an ARFOR gives
> > you a QNH, then it is related to one well defined spot on the surface.
>
> As I understand it ( In Australia) the QNH in an ARFOR must be within
> 5 mbar of the "real QNH"  - ie what gives you field elevation for any
> place within that area. otherwise the area will be broken up into sub
> areas and no 2 adjacant sub areas must differ by more than 5 mbar.
> That way the errors which Wing flap alludes to, and must certainly
> exist in non ISA atmosphere, would result in errors of no more than
> 150 feet between aircraft using either the correct AFROR QNH or the
> airfield set QNH

Yep. Altough I think I've seen pretty big local QNH changes without
the ARFOR areas being broken up but I can't recall them being bigger
than 5hPa.

Cheers

On Apr 18, 11:04 am, Bertie the Bunyip <A...@AA.AA> wrote:
> Stefan <stefan@mus._INVALID_.ch> wrote in news:c9458$4807bcae$54487328$4551
> @news.hispeed.ch:
>
> > WingFlaps schrieb:
>
> >> Perhap we are at crossed purposes but an ARFOR does not refer to an
> >> airfield -that's a METAR and not all fields issue them. So in this
> >> case how can QNH give field elevation unless it's an ISA day?
>
> > Again: QNH gives *by definition* the field elevation.
>
> Only at the airport ref point, so, no, it doesn't.
>
He'll get it in the end... high to low look out below! I'll guess he's
not flown Xcountry to non ATIS fields?

Cheers

On Apr 18, 9:05 am, Bertie the Bunyip <A...@AA.AA> wrote:
> terry <tfm...@iprimus.com.au> wrote in news:375462b0-66e7-4ed0-b45d-
> e6e089f79...@s50g2000hsb..com:
>
>
>
>
>
>
>
> > On Apr 18, 7:10�am, Stefan <stefan@mus._INVALID_.ch> wrote:
> >> WingFlaps schrieb:
>
> >> > Perhap we are at crossed purposes but an ARFOR does not refer to an
> >> > airfield -that's a METAR and not all fields issue them. So in this
> >> > case how can QNH give field elevation unless it's an ISA day?
>
> >> Again: QNH gives *by definition* the field elevation. If an ARFOR
> gives
> >> you a QNH, then it is related to one well defined spot on the
> surface.
>
> > As I understand it ( In Australia) the QNH in an ARFOR must be within
> > 5 mbar of the "real QNH"  - ie what gives you field elevation for any
> > place within that area. otherwise the area will be broken up into sub
> > areas and no 2 adjacant sub areas must differ by more than 5 mbar.
> > That way the errors which Wing flap alludes to, and must certainly
> > exist in non ISA atmosphere, would result in errors of no more than
> > 150 feet between aircraft using either the correct AFROR QNH or the
> > airfield set QNH
>
> Yipes! Are you studying to be an astronaut?
>
Are there any openings?

Terry,

> So what do you
> call the number you dial up to make the altimeter read airport
> elevation?
>

altimeter setting. It is given in inches Hg, too, with 29.92 being
equivalent to 1013 hectoPascal. The Brits use another non-SI unit,
namely millibars, which is the same as hectoPasal.

--
Thomas Borchert (EDDH)

On Apr 18, 6:56 pm, Stefan <stefan@mus._INVALID_.ch> wrote:
> WingFlaps schrieb:
>
> > BINGO! That's right, setting QNH on an altimeter DOES NOT does give
> > field elevation UNLESS it's issued for that field :-)
>
> Which has been pretty obvious, hasn't it? But I forgot that this is Usenet..

Nope it's not Usenet, it comes back to correcting the erroneous idea
that setting QNH on an altimeter makes it faithfully report altitude.

Cheers

In rec.aviation.student Andy Hawkins <andy@gently.org.uk> wrote:
> The PAN actually sounds to me like a good idea, but as I always say I'm
> still a lowly stude! Being able to differentiate between a Mayday (basically
> aircraft in imminent danger) and PAN (something that needs priority but
> nothing that will endanger the aircraft in short order) seems like a good
> idea to me.

Given the rarity of emergency calls, it seems like the important thing is
to make the emergency known in a simple and easy fashion first, then work
out the details later on as they're needed. The distinction is useful, but
I think that it's not worth putting extra workload on the pilot to figure
out just what degree his emergency is in his moment of crisis.

--
Michael Ash
Rogue Amoeba Software

On 04/18/08 08:38, Michael Ash wrote:
> In rec.aviation.student Andy Hawkins <andy@gently.org.uk> wrote:
>> The PAN actually sounds to me like a good idea, but as I always say I'm
>> still a lowly stude! Being able to differentiate between a Mayday (basically
>> aircraft in imminent danger) and PAN (something that needs priority but
>> nothing that will endanger the aircraft in short order) seems like a good
>> idea to me.
>
> Given the rarity of emergency calls, it seems like the important thing is
> to make the emergency known in a simple and easy fashion first, then work
> out the details later on as they're needed. The distinction is useful, but
> I think that it's not worth putting extra workload on the pilot to figure
> out just what degree his emergency is in his moment of crisis.
>

If the pilot is in a moment of crisis, then an emergency should be declared.
PAN is used when it is not at that level.


--
Mark Hansen, PP-ASEL, Instrument Airplane, USUA Ultralight Pilot
Cal Aggie Flying Farmers
Sacramento, CA