On Thu, 17 Apr 2008 14:54:53 +0000 (UTC), Bertie the Bunyip
wrote:

terry wrote in news:179c2f21-99ad-4415-a9b2-
:

On Apr 18, 12:07*am, Bertie the Bunyip wrote:
terry wrote in news:234756e2-a583-4cbc-8f42-
:

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 f
olks)
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!.


Yer right, of course, I just couldn't resist the joke! There's a name
for that, if I'm not mistaken, and it's QNE. But theyre going for A, I'm
pretty sure and made an error in what thye were trying to say in C. I'm
bi-barometric, BTW.

Bertie

bi-barometric? is that as bad as being queer :-)