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 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!.