QNH
07-18-2014 | 09:41 AM
#1
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QNH
Hello everyone
I understand that the QFE is the pressure at the airfield and the QNH is the actual pressure at airfield reduced to sea level using ISA. But I can't understand why at high elevation airports the QNH value is high (i.e QNH 1030). Any ideas?
I understand that the QFE is the pressure at the airfield and the QNH is the actual pressure at airfield reduced to sea level using ISA. But I can't understand why at high elevation airports the QNH value is high (i.e QNH 1030). Any ideas?
07-18-2014 | 11:29 PM
#3
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07-19-2014 | 08:18 AM
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From: Sr. VP of button pushing
Corrected to sea level would be better way of saying it. The normal pressure lapse rate down low (say sea level to 10,000 feet) is about 100 for every .1 of an inch of Hg. So on a standard day the actual pressure in New Orleans is 29.92 and in Denver it'll be about 24.32. The Met people in Denver have a correction factor they add to the actual pressure to bring it up to 29.92. We could use the local pressure and everything would be QFE.
Believe it or not, the world does not revolve around pilots. The weather wizards use pressure to figure out where fronts are and what's going to happen. If everyone just used their local pressure uncorrected for altitude, drawing isobars on a weather map would be useless.
Believe it or not, the world does not revolve around pilots. The weather wizards use pressure to figure out where fronts are and what's going to happen. If everyone just used their local pressure uncorrected for altitude, drawing isobars on a weather map would be useless.
07-19-2014 | 09:14 AM
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From: Left seat on a kite
That's the procedure AA used for years until thy drug a few planes through the trees and approach lights. Most line pilots I've spoken to about it say they liked it.
07-19-2014 | 09:23 AM
#8
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From: I pilot
The RAF (UK) still like to use QFE, and QFE is also used in some parts of Eastern Europe and Asia. A friend of mind requested QNH somewhere in the 'stans but was given QFE, and luckily caught on before he bent some metal.
07-19-2014 | 10:02 AM
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Thats my question.. Because at Addis Abeba airport for example the elev is 7700ft the QNH is always high as 1030 hPa or something
Last edited by FlyFly; 07-19-2014 at 10:23 AM.
07-19-2014 | 02:33 PM
#10
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From: Baja Vermont
Flyfly,
There are many locations where a fairly permanent high pressure atmosphere exists, Addis near the Equator is likely one. Quito and La Paz, Bolivia is also under that high pressure influence. What you are seeing is an atmospheric effect, not a QNH effect.
GF
There are many locations where a fairly permanent high pressure atmosphere exists, Addis near the Equator is likely one. Quito and La Paz, Bolivia is also under that high pressure influence. What you are seeing is an atmospheric effect, not a QNH effect.
GF
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