terry

On Apr 17, 11:38 pm, Stealth Pilot <notranspon...@aeroplanes.com.au>
wrote:
> On Thu, 17 Apr 2008 07:30:56 -0400, "Barry" <a...@b.c> wrote:
> >> 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.
>
> >I agree with you - answers a and c are both correct.  Day 2 QNH is about 1026.
>
> playing with an altimeter here in my lap.
> simulating 1390 by setting 390. the qnh reads as 1032.
>
> moving the needle lower sees the qnh values going lower.
>
> so to correct for the reduced reading I would need to move the qnh the
> other way.(increase it)
> I agree a is correct from playing with an actual altimeter.
> c is correct just from reading the data in the question.
>
> fwiw
> Stealth pilot- Hide quoted text -
>
gday Stealth,
I just think of an altimeter as being a inverse pressure guage cos
pressure decreases with altitude, so for altitude reading to have gone
down , atmospheric pressure has to have gone up.
I gotta ask, why have you got an altimeter in your lap?
Terry