dc-10 levo
Posts: 3376
Joined: Mon Nov 19, 2001 3:22 am

What Does QNH Mean?

Sat Apr 12, 2003 7:52 pm

 Smile Hi everyone!  Smile

Sometimes when I listen on my scanner I hear something like:

"East Midlands Approach, good morning Golf Charlie Uniform with you 3,000ft."

The controller will respond and then the pilot will say something like:

"QNH (some numbers) Sqwark 2846."

What does QNH mean?

Thanks for your replies.

DC-10
 
ben88
Posts: 1037
Joined: Fri Dec 31, 1999 4:49 pm

RE: What Does QNH Mean?

Sat Apr 12, 2003 8:02 pm

Barometer

sdfsdfsdfsdfsdfsdfds
 
Sabena 690
Posts: 6065
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RE: What Does QNH Mean?

Sat Apr 12, 2003 8:02 pm

Isn't that for the transponder code?

No idea otherwise...

EDIT: now I remember: hasn't this something to do with the barometer? Because they say a lot QNH 1013...

[Edited 2003-04-12 13:03:48]
 
LYNDON
Posts: 125
Joined: Wed Aug 22, 2001 6:45 pm

RE: What Does QNH Mean?

Sat Apr 12, 2003 8:04 pm

Think its something to do with the air pressure and it affects an aircrafts altimeter ?
 
OPNLguy
Posts: 11191
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RE: What Does QNH Mean?

Sat Apr 12, 2003 8:18 pm

Q-codes have been around for awhile, as you can see.

http://www.kloth.net/radio/qcodes#qaa

QNE and QNH are listed towards the end of the first section.

When ATC gives an aircraft its QNH (expressed in inches of mercury here in the US, or hectopascals elsewhere), the crew then sets their aircraft altimeters to that setting, so that their displayed altitude is with reference to that airport.
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dc-10 levo
Posts: 3376
Joined: Mon Nov 19, 2001 3:22 am

RE: What Does QNH Mean?

Sat Apr 12, 2003 9:34 pm

Oh, thanks for the help.

(I've even heard it whilst listening to police aswell, but I think thats just QNE.)

DC-10
 
Skymonster
Posts: 3428
Joined: Fri Oct 12, 2001 7:53 pm

RE: What Does QNH Mean?

Sat Apr 12, 2003 9:40 pm

The value given after the QNH (e.g. East Midlands QNH one-zero-one-three) is the value that has to be set on the airplane's altimeter to make the altimeter display the aircraft's altitude above mean-sea-level. If the East Midlands QNH is one-zero-one-three, setting 1013 on the airplane's altimeter whilst the airplane is on the ground at East Midlands will result in the altimeter showing around 300 feet depending on exactly where the airplane is at EMA, as 300 feet is the approximate elevation of East Midlands Airport.

QNH has to be set on the altimeter because the air pressure at a specific location varies day by day, hour by hour, minute by minute, and this affects the altimeter's reading. To ensure that all airplanes are using the same setting and reference point, all airplanes operating in or near an airfield set the airfield's local QNH.

Setting QNH makes an altimeter show altitude above mean sea level, whereas setting QFE (which you will also have heard) makes an altimeter show height above the airfield elevation - in the UK, QFE is usually used for landings so that the altimeter reads zero on touchdown, QNH is used for flying around the general area as pressure can vary from area to area and this ensures that everyone is using the same value.

At East Midlands, the QNH will usually be around 10 higher than the QFE (e.g. QNH 1013, QFE 1003) as each hectopascal is the equivalent of approximately 30 feet - the total difference of 10 hectopascals represents 300 feet, which again is the approximate height of EMA above sea level.

Hope this helps,

Andy (private pilot flying from East Midlands from time to time!!!)
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tsentsan
Posts: 1921
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RE: What Does QNH Mean?

Sat Apr 12, 2003 9:45 pm

If you want to know what QNH stands for, it means... Question Nil Height. This goes back to older times where a/c wanted to know what was the pressure at 0 height which was the airport elevation.

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dc-10 levo
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RE: What Does QNH Mean?

Sat Apr 12, 2003 10:04 pm

Thanks guys!

DC-10
 
avroarrow
Posts: 804
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RE: What Does QNH Mean?

Sat Apr 12, 2003 11:17 pm

And to think, over here we just call it the altimeter setting when dealing with ATC and ATIS.  Smile/happy/getting dizzy
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timz
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RE: What Does QNH Mean?

Sun Apr 13, 2003 7:13 am

I think Skymonster covered it; Tsentsan was the one that got careless.
 
Snoopy
Posts: 355
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RE: What Does QNH Mean?

Sun Apr 13, 2003 7:42 am

"If you want to know what QNH stands for, it means... Question Nil Height. This goes back to older times where a/c wanted to know what was the pressure at 0 height which was the airport elevation."

Just to be picky  Smile

QNH actually gives the air pressure at sea-level. If you set this on your altimeter, your altimeter will show the airfield altitude when you are on the tarmac.

If you set QFE, which is the air pressure at airport altitude (Field Elevation), your altimeter will show "0" on the tarmac.
 
lamyl_hhlco
Posts: 596
Joined: Tue Aug 08, 2000 8:28 am

RE: What Does QNH Mean?

Sun Apr 13, 2003 2:45 pm

it's simply the athmospheric pressure above sea level, equivalent as Altimeter pressure in US.
 
tsentsan
Posts: 1921
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RE: What Does QNH Mean?

Sun Apr 13, 2003 3:52 pm

Apologies, muz have mixed them up somewhere  Sad But thanks good for learning Big grin
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MarkTPA
Posts: 94
Joined: Thu Jun 08, 2000 1:54 pm

RE: What Does QNH Mean?

Mon Apr 14, 2003 3:16 am

I think the guys above covered it well. It is another way of stating the Altimeter setting. I hear it all the time when I fly into NAS or FPO.

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