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Questions tagged [qnh]

QNH is a Q codes defined as the barometric pressure at an airport adjusted to sea level using the ICAO Standard Atmosphere. On the ground, an altimeter set to QNH reads the elevation of the airport.

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What is meant by altitude correction above Transition level?

I am a system engineer dealing with Thales ATC product. In my system there is a server called sensor data processor, one of its function is to receive QNH data to do altitude correction. I can't ...
mahmoud youssef's user avatar
4 votes
2 answers
181 views

How to determine QNH zones like New Zealand did?

I saw a file stating that New Zealand has 11 zones and was wondering how it was determined and divided, does anyone have any idea? the paper offers a short description that doesn't cover much ...
Zol613's user avatar
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Which countries use qfe field pressure?

I heard that acrobatic flight, Russians, Americans use qfe but is it always the case? Also why doesn't everyone use it? Isn't qfe field pressure better than qnh local pressure... Does a pilot ever use ...
Yosef Jabbour's user avatar
6 votes
3 answers
2k views

How many times does a pilot usually change local pressure while landing or departing?

The local air pressure (QFE, and therefore QNH as well) may change throughout the day. ATC will advise pilots of the new altimeter setting on a regular basis. How often do pilots truly update this ...
Yosef Jabbour's user avatar
-6 votes
1 answer
207 views

find the height of the aircraft [closed]

The elevation of Airport A is 150ft AMSL and Airport B is 500FT AMSL. The QNH at A is 1013hPa and at B is 998hPa. An aircraft is overhead A with 5000ft indicated on the altimeter with 1013hPa set on ...
Izzuddin Cheras's user avatar
4 votes
3 answers
2k views

Relation between altimeter setting (QNH) formula and the barometric formula

I'm searching for a reliable source for a formulization of the QNH adjustment to the barometric altitude. I found this document from weather.gov that gives a formula for the Altimeter Setting, which ...
Melih Durmaz's user avatar
2 votes
2 answers
757 views

How can I work out Sea Level Pressure from QNH?

I am a little confused, is the QNH the current pressure at Sea Level? Therefore putting it into the altimeter will give your current altitude on the ground in pressure altitude relative to current sea ...
Mikey Patterson's user avatar
3 votes
1 answer
270 views

What geographic reference system do airport towers use?

What geographic reference system (WGS84, EGM96, EGM2008 etc.) do airport towers use when measuring things like aiport elevation and current QNH for airport? Is there even a commonly accepted one ...
Melih Durmaz's user avatar
3 votes
2 answers
2k views

How is Altitude/QNH defined state when passing transition altitude?

Let's say an airplane is climbing towards transition altitude (TA = 5000 ft), and it has it's altimeter set to QNH = 1030 hPa. ...
Ondrej Telka's user avatar
2 votes
1 answer
2k views

Why does the QNH of an aircraft change or need to be changed?

This is mainly a 3 part question. First, is it the QNH of of the aircraft? of the aerodrome? of the region or area? Or am I understanding it wrong my looking at it like that? If the QNH is set ...
user44056's user avatar
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1 answer
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Why is True Altitude calculated using the difference from the QNH to 1013hPa?

I have an example for true altitude calculation. The given Information is QNH: 983hPa, cruise in FL 85, ISA -10°C in this Alt. The math and calculations are not hard and i also get to the correct ...
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7 votes
3 answers
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What’s the setting range altimeters can handle?

What’s the setting range altimeters can handle? Is there a standard requiring a certain range for aircraft to be certified? Are there many occasions where a QNH is so high or low that airplanes have ...
Florian's user avatar
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5 votes
1 answer
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Is it possible to get the QNH value in Austria using a web service?

I got a altimeter sensor which can be connected to a computer and can be adjusted by the QNH! I need the QNH for Austria, I figured out that the current QNH of the airports are streamed via radio. ...
mstranne's user avatar
2 votes
1 answer
324 views

Why is there a provision of pressure setting in GPS?

Some of the GPS have a provision of setting barometric pressure (QNH/QFE). How does it work?
Adder's user avatar
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How does changing the altimeter setting in the US and elsewhere compare?

I have been trying to track down an answer to this question and I stumbled upon this website. Apologies if this answer is already out there. I have seen the FAR regulation, 14 CFR 91.121 - Altimeter ...
TexAg09's user avatar
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What is wrong about this interpretation of QFE and QNH?

I'm a little confused about the QFE and QNH definitions, and its application on aviation. I learnt that: $QFE$ = pressure measured by an altimeter which is adjusted to ground level (it gives a height ...
Élio Pereira's user avatar
12 votes
3 answers
67k views

How can I calculate QNH from QFE?

Can someone please explain in simple terms how to work out your QNH from QFE? For example, you take off at 0' but leave the circuit, what do you set the altimeter to? How do you know the QNH?
user13555's user avatar
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What is the meaning of "altimeter three-zero-one-one"?

I've been listening to a lot of liveatc.net recently (mostly at CYVR). What does it mean when the ATC give an "altimeter" reading (usually around the 3000 area). Altimeter three-zero-one-one. I'm ...
Jim's user avatar
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9 votes
3 answers
7k views

When is QFE used?

When is QFE, instead of QNH, used for the altimeter setting? QFE: If you set the subscale of your altimeter to read ... millibars, the instrument would indicate its height above aerodrome elevation ...
user avatar
9 votes
3 answers
2k views

How does ATC handle changing QNH/altimeter values?

Obviously for aircraft arriving to or departing from an airport/airspace (as relevant), they listen to the ATIS and/or are given the QNH. But what happens if that pressure changes? Even a fairly ...
Jon Story's user avatar
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Do pressure altimeters take into account differences in temperature? [duplicate]

I work as ATC in Korea and recently, I have some question about winter altimeter setting. In my facility, we use winter altimeter adjustment because the aircraft's pressure altitude is lower than ...
user12972's user avatar
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10 votes
2 answers
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Why does the MH370 ATC transcript never mention QNH? When is QNH given to aircraft?

Looking at the ATC transcript from MH370, I noticed that nowhere is the QNH communicated to the aircraft. That seemed odd to me... it seems that every time I talk to a tower or airways they tell me ...
user998303's user avatar