WingFlaps

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