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17th April 2008, 10:17 AM

On Apr 18, 12:07 am, Bertie the Bunyip <A...@AA.AA> wrote:
> terry <tfm...@iprimus.com.au> wrote in news:234756e2-a583-4cbc-8f42-
> 9fc499a48...@c65g2000hsa..com:
>
> > I am confused by this practice commercial nav question. ( at least I
> > am confused by the answer in the book which was b. but I think both a
> > and c are correct), but I appreciate some other opinions.
>
> > Day 1 Altimeter reads elevation of 1390 feet with 1013 HPa set on
> > subscale
> > ( thats equivalent to 29.92 inches of Hg for the US folks)
> > Day 2 Altimeter reads elevation of 1000 feet
> > Assuming the altimeter subscale was not changed between day 1 and day
> > 2 it could be said that
>
> > a. The QNH is higher on day 2
> > b. The QNH is lower on day 2
> > c. The pressure altitude at the airport is lower on day 2
> > d. The atmospheric pressure at the aerodrome has not changed.
>
> It's A. It could also be C if the airfield has a serious subsidance
> problem.
>
you are really confusing me now Bertie, I got learned that the
pressure ht was wot your altimeter reads when you have 1013.2 in the
window ( or 29.92 for you ...or maybe not cos everyone knows bunyips
are aussies ) 1000 is lower than 1390 therefore pressure altitude is
lower on day 2.. surely!.

17th April 2008, 10:17 AM	#7 (permalink)
terry Guest Posts: n/a Classified Rating: % ()	Altimeter Question On Apr 18, 12:07 am, Bertie the Bunyip <A...@AA.AA> wrote: > terry <tfm...@iprimus.com.au> wrote in news:234756e2-a583-4cbc-8f42- > 9fc499a48...@c65g2000hsa..com: > > > I am confused by this practice commercial nav question. ( at least I > > am confused by the answer in the book which was b. but I think both a > > and c are correct), but I appreciate some other opinions. > > > Day 1 Altimeter reads elevation of 1390 feet with 1013 HPa set on > > subscale > > ( thats equivalent to 29.92 inches of Hg for the US folks) > > Day 2 Altimeter reads elevation of 1000 feet > > Assuming the altimeter subscale was not changed between day 1 and day > > 2 it could be said that > > > a. The QNH is higher on day 2 > > b. The QNH is lower on day 2 > > c. The pressure altitude at the airport is lower on day 2 > > d. The atmospheric pressure at the aerodrome has not changed. > > It's A. It could also be C if the airfield has a serious subsidance > problem. > you are really confusing me now Bertie, I got learned that the pressure ht was wot your altimeter reads when you have 1013.2 in the window ( or 29.92 for you ...or maybe not cos everyone knows bunyips are aussies ) 1000 is lower than 1390 therefore pressure altitude is lower on day 2.. surely!.