Altimeter Question

terry 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.


Their answer confuses me too. It seems that if the altimeter setting wasn't
changed from day 1 to day 2, yet it reads a lower altitude, the barometric
pressure must have risen. The altimeter will translate lower pressure to higher
altitude and higher pressure to lower altitude. So I think the answer should be
"a". And if I accept "a", I have to accept "c" as well, as you did.

I'm probably going to regret posting this because I'm going off the top of my
head but it wouldn't be the first time a test guide had the wrong answer posted.

Alright guys.... pile on!




--
Mortimer Schnerd, RN
mschnerdatcarolina.rr.com

On Apr 17, 9:29*pm, "Mortimer Schnerd, RN" mschnerdatcarolina.rr.com
wrote:
terry 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.

Their answer confuses me too. *It seems that if the altimeter setting wasn't
changed from day 1 to day 2, yet it reads a lower altitude, the barometric
pressure must have risen. *The altimeter will translate lower pressure to higher
altitude and higher pressure to lower altitude. *So I think the answer should be
"a". *And if I accept "a", I have to accept "c" as well, as you did.

I'm probably going to regret posting this because I'm going off the top of my
head but it wouldn't be the first time a test guide had the wrong answer posted.

Alright guys.... pile on!

No, its not the first time I have come across wrong answers either,
but it is the first time I have come across a wrong answer, pointed it
out to the author and was still told I was wrong. ( I dont want to
name the said author because I think he otherwise has published some
very good material and I am sure he will soon realise his mistake.. I
just wanted to be absolutely sure I was right before I responded to
his response!)
Thanks Mort