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Altimeter Question
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. Terry PPL Downunder |
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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 |
#3
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Altimeter Question
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. |
#4
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Altimeter Question
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 |
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Altimeter Question
On Apr 17, 9:30*pm, "Barry" 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. Yep, thats what I get Thanks |
#6
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Altimeter Question
On Thu, 17 Apr 2008 02:20:46 -0700 (PDT), terry
wrote in : 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 http://en.wikipedia.org/wiki/Mbar Atmospheric air pressure is often given in millibars where "standard" sea level pressure is defined as 1013.25 mbar (hPa), equal to 1.01325 bar. Despite millibars not being an SI unit, they are still used locally in meteorology in some countries to describe atmospheric pressure. The SI unit is the pascal (Pa), with 1 mbar = 100 Pa = 1 hPa = 0.1 kPa. Meteorologists worldwide have long measured air pressure in millibars. After the introduction of SI units, others use hectopascals (which are equivalent to millibars) so they could stick to the same numeric scale. Similar pressures are given in kilopascals in practically all other fields, where the hecto prefix is hardly ever used. In particular, Canadian weather reports use kilopascals (which could also be called centibars). ( 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. Terry PPL Downunder http://www.acronymfinder.com/acronym.aspx?rec={8F1A7DDE-89E8-11D4-8351-00C04FC2C2BF} What does QNH stand for? Atmospheric Pressure (Q) at Nautical Height (aviation) |
#7
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Altimeter Question
Larry Dighera schrieb:
http://en.wikipedia.org/wiki/Mbar Mbar would be a tad much. You certainly meant mbar. What does QNH stand for? Atmospheric Pressure (Q) at Nautical Height (aviation) Bull****. QNH is *not* an acronym. It's one of over hundred Q-Codes which were defined in the stone age of radio telephony. The letters were randomly chosen, think of it as a numeration. Most of those Q-Codes are forgotten today, but a few still live. In aviation, I mean in aviation in all coutries except the USA, QNH, QFE and QNH are used to define different altitude settings (roughly spoken). QNH stands for the pressure you must tune in the kollmans window to have the altimeter display the airport elevation when the airplane sits on the ground. (As opposed to QFE, which ist the pressure to set for the alitmeter to display zero on the ground and QNE, which is the altitude which the alitmeter shows on the ground when it is set to standard atmosphere.) For those who believe in Wikipedia: http://en.wikipedia.org/wiki/Q-code |
#8
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Altimeter Question
On Thu, 17 Apr 2008 07:30:56 -0400, "Barry" 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 |
#9
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Altimeter Question
On Apr 18, 1:29*am, Stefan wrote:
Larry Dighera schrieb: *http://en.wikipedia.org/wiki/Mbar Mbar would be a tad much. You certainly meant mbar. * What does QNH stand for? * Atmospheric Pressure (Q) at Nautical Height (aviation) Bull****. QNH is *not* an acronym. It's one of over hundred Q-Codes which were defined in the stone age of radio telephony. The letters were randomly chosen, think of it as a numeration. Most of those Q-Codes are forgotten today, but a few still live. In aviation, I mean in aviation in all coutries except the USA, QNH, QFE and QNH are used to define different altitude settings (roughly spoken). QNH stands for the pressure you must tune in the kollmans window to have the altimeter display the airport elevation when the airplane sits on the ground. (As opposed to QFE, which ist the pressure to set for the alitmeter to display zero on the ground and QNE, which is the altitude which the alitmeter shows on the ground when it is set to standard atmosphere.) For those who believe in Wikipedia:http://en.wikipedia.org/wiki/Q-code QNH means query Newquay Harbour which was the British reference for sea level. It should give the atmospheric pressure at that dtaum -but I doubt that the met offices bother to check what the actual height of that datum is... Cheers |
#10
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Altimeter Question
On Apr 17, 11:38*pm, Stealth Pilot
wrote: On Thu, 17 Apr 2008 07:30:56 -0400, "Barry" 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 |
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