QNH
 

What exactly does this acronym stand for and where did it originate?

It stands for "Question Nil Height"

Used back in the days when morse code was used. They would ask for QNH through morse code, and get the atmospheric pressure at sea level.

Im sure someone will have more to add, but thats the basics of what it means.

QNH
 

http://www.kloth.net/radio/qcodes.php

This should answer the question. Good for the boaty floaty gang too.

It's not an acronym, or an abbreviation, but just one of a whole host of three-letter codes in the Q-Code system. I think Aussie's answer is simply the result of somebody finding some words that fit - almost. After all, QNH has nothing to do with height.

The system originated in the days of morse code, where a simple three-letter code could replace perhaps a lengthy sentence, and save a lot of time. It also meant the message could be understood instantly, in any language, and without any ambiguity.

I'm guessing it's a Q code because there are no three-letter English words that begin with Q, so as soon as one is received it is obvious that it has a special meaning.

The Q certainly stands for Question, but I was under the impression that NH was for Nautical Heightm afterall it is an elevation above sea level that QNH represents............... incoming??

Farmer1 has it bang on.

The Q "codes" are exactly that - codes. I've had a protracted discussion with a non-comms (in the radio operator sense) colleague who had it as an acronym in some safety docs a few months ago. I eventually managed to get it correctly descibed in the glossary that was in the document he was scribing.

Pedantic to the end .... :ouch:

ST

Query/Question Newlyn Height
 

Feel free to correct me anyone if this is wrong.

I was told that QNH stands for QUESTION/QUERY NEWLYN HEIGHT.

The original sea level pressure in the UK was always based on the pressure at Newlyn in Cornwall. The OS (Ordanance Survey) website defines ODN (which defines the height of any point in the UK) as Ordanance Datumn Newlyn. ODN is used as defined in the following quote from the OS website.

This is our national coordinate system for heights above mean sea level (orthometric heights). It was originally based on tide gauge readings at Newlyn, Cornwall. ODN is the usual definition of height above mean sea level in mainland Britain and some islands.



Newlyn is the home of the UK National tidal centre.
And historically is where UK National sea level pressure is defined from.

And before anyone says QNH is an altitude, a QNH pressure setting defines your altitude or height above mean sea level. So by flying on a QNH you are flying a height (altitude if refering to it correctly on the RT) above MSL. Just as you would be flying a height agl if using a QFE.

I have read various accounts in books and the internet as to which came first QNH or Question/Query Newlyn Height.
By this I mean is QNH an acronym or is Question Newlyn Height a useful pneumonic for QNH.
If anyone knows the answer please tell me.

This could all be a load of tosh, but never heard a better explanation or had it dissproved.

CMO

Then there is QFE which is the pressure setting to apply to your altimeter to result in close to zero altitude indicated at the airfield datum.

The closest I can get to unscrambling QFE as though it is an acronym is Quick Find Earth!!

Airfield datum begs the question. Where normally is the airfield datum particularly in relation to the nominal GPS position or INS setting.

What other Qs relate to atmospheric pressure. I've forgotten because I don't think they matter much or have become obsolete.

QFE is Question/Query Field Elevation

In the Wikipedia at http://www.answers.com/main/ntquery;...a&linktext=QNH
See also http://www.answers.com/topic/q-code

<<What other Qs relate to atmospheric pressure.>>

Well there's QNE for high altitude airports.. My brain cells are long dead but I think it's used at places where it would not be possible to unwind the altimeter to read the QNH. It's where you set the altimeter to a particluar (standard?) setting and you're told the altitude it will read on touch down.. Someone please confirm.

Have those who are trying to fit words to the codes read the initial link by albatross?

There may be well known mnemonics to aid memory of often used codes - and possibly even assisted in their initial allocation, but essentially the codes came before the widely used 'memory aids' - one only has to look at the number of them to seee that they cannot all stand for something.
Possibly those who only hear QHN/QFE don't realise the number of others and assume those two must have a meaning.

Even today - in the ATPL we have (including mnemonics I was taught):
QDM: Mag heading to [Direct Magnetic]
QDR: Mag Bearing from [Direct Radial]
QTE: True bearing from [True Eminanting (from)]
QUJ: True track to [True to the flag (Union Jack - starting to reach a bit I know!)]

And I have certainly used:
QSY: Leaving frequency (normally with mil controllers)
QGH: According to the link it is simply asking for clearance to use an approach - I was under the impression it was itself a specific type of approach where ATC homes in on your tranmission (instead or RADAR) and talks you down. Done a few (with real RADAR backup - I may be stupid but I'm not suicidal!)

Edited:

HD, from albatrosses link:
QNE: What indication will my altimeter give on landing at ... (place) at ... hours, my sub-scale being set to 1013.2 millibars (29.92 inches)?

On landing at ... (place) at ... hours, with your sub-scale being set to 1013.2 millibars (29.92 inches), your altimeter will indicate ... (figures and units).

Just to repeat ....
'Q' codes ARE NOT MNEMONICS - they are a series of three letter combinations which were, initially, used in W/T (morse code) transmissions to aid international understanding and for brevity. For military use there was also the 'Z' code which operated similarly. The 'Q' had no query significance, it was just a common starting letter. If the code was used as a query, rather than a statement, it preceded the additional 'code' IMI (sent as one continuous character). The equivalent interrogative for the 'Z' code was INT.
Their continuing use in R/T is indicative of their universality.

Re QNE
 

To set QNE is to set the standard pressure setting of 1013hpa - ie when passing the transition altitude. It would never be used for landing unless the QNH (or QFE if used) just happened to be 1013.

Apollo 100 - incorrect I'm afraid

QNE is NOT 1013mb - that is the Standard Altimeter Setting

QNE IS (As HD says) occasionaly used at High Altitude Airports and is the level indicated on an altimeter, on the ground at that location, when 1013 is set.

It's a common misunderstanding which does keep cropping up however.

:ugh:
Do I not dislike altimeter questions?

QNE is 1013 millibars. Set at transition level and reset at transition altitude.
All aircraft with 1013 set will indicate a flight level which is then a standard for all aircraft with 1013 so set.

QFE is that setting which will allow the altimeter to read 0ft at the touchdown reference point. It was much favoured by the military and is still in use.
Therefore, go around height might be at 200ft, altimeter reading.

QNH is the setting which will allow the altimeter to read airfield elevation at the touchdown reference point.
It is used at high airfields such as Johannesburg where it is not possible to wind down the altimeter sufficiently to allow 0ft to be read on touchdown.
Therefore go around height might be at 5,780ft, altimeter reading.

Does that help muddy the waters?:D

MATS Pt 1 App 'A' page 2 gives QNE values and an explanation of their use.

Not quite, I don't think, Chilli. I don't think it has anything to do with the airport's elevation, but the pressure. If the QNH is outside the range of the altimeter's setting, then that is when QNE is used.

We used to use it offshore, which is not a place noted for its high elevations. The radio op would have two altimeters - one set to give QFE, and the other with the adjustment inhibited, and set to 1013. He would give us QFE and QNE. We would set QFE on one altimeter and 1013 on the other, and confirm the QNE. The simple process checked all four altimeters as well as the radio op and the pilots.

Dead simple, and absolutely foolproof.



Except:

I paid a visit to the radio room once, and an aircraft called. The radio op gave the QFE, and then consulted a chart before giving the QNE.

There had never been a second altimeter, and someone in the dark and distant past had produced the QNE chart. The radio op was more than a bit upset when I tore up the chart, because he would no longer be able to provide the QNE. No amount of explanation on my part could make him understand how dangerous his practice could be.

The QNE is set when altimeters cannot be set to other pressures. La Paz in Bolivia is, I believe, a classic example of where it is used.

Farmer1.... Why would QNE be used offshore instead of QNH as it complicates matters? The pressure on the surface rarely becomes so high or low that it would be outside the subscale of most altimeters.

HD,

Because it enables you to check the accuracy of the altimeter in the radio room, and also the radio op. Bear in mind he is a radio op, not an ATCO, and at one time did not need any experience or instruction in aviation matters in order to get the job. I remember one who had never heard of the term QFE, for instance, and was told of another who was busy looking in a drawer for said item.

QFE is universally used, QNE was supposed to be a safety bonus.

A question for you: Can you explain why La Paz cannot use QNH?

QBI = Fog. Quite Bloody Impossible.:eek:

'cos with all that cocaine around EVERYTHING is high

:eek:

It seems to me that on the subject of the QNHs, QFEs, and QNEs, some of us; and I do not exclude myself; might just need to go back to ground school before another mountain materialises out of the mist to go boom in the gloom.
Where's young Danny or the man from the Barad Dur or the Delphic Rainboe to settle this little discussion?:\ :ooh:

Brimstone,

Brilliant! Thanks for that.

Farmer.

High elevation airfields issue QNH settings.

The (UK) met office defines QNE as follows : "QNE is only used when the pressure is so low or so high that the altimeter subscale will not go up or down far enough to select the correct QFE - thus a pressure is assigned so that the altimeter reads a specific (known) height when the aircraft is on the ground - that is the QNE."

QNH is defined thus : "QNH is used to set the altimeter to read the actual height above sea level in the local area. This is also passed by the local ATC and so when the aircraft is on the ground with QNH set, the altimeter will show the height of the airfield."

Normally a high elevation airfield would issue a QNH the same as any other airfield. The current metar for La Paz Bolivia (elev 13,355ft) at the time of writing is :
2006/02/25 22:00
SLLP 252200Z 14004KT 9999 FEW017 FEW020CB SCT070 BKN200 10/02 Q1033

The last figure being the QNH.

Nairobi Kenya (elev 5327ft):
2006/02/25 21:00
HKJK 252100Z 01005KT 9999 FEW020 20/13 Q1020 NOSIG

The last figure being the QNH

Mexico city (elev 7341ft):
2006/02/25 21:45
MMMX 252145Z 31010KT 7SM FEW030 26/01 A3024 RMK 8/500 HZY.

A3024 being the altimeter settings in inches of mercury ( and hundredths) or as we know it the QNH.


Quito Equador ( elev 9223ft):
2006/02/25 22:00
SEQU 252200Z 34008KT 9999 BKN040 BKN100 15/12 Q1023 NOSIG.

The last figure being the QNH.

All these airfields are between 5327ft elev' and 13,355 ft elev.

These are the metar reports, the ATIS information and the altimeter settings being passed to arriving and departing aircraft.

:hmm:
More dust from the sands of Africa. I would draw your attention to the obvious use in practical terms of QNE in order to determine flight levels and its redundancy as a datum for ground operations.:)

Q-codes
Note: the letters in the Q-code nomenclature have no literal significance, these are remnants of an extensive notation system from the days of wireless-telegraphy. There were some 200 three letter Q-codes each representing a sentence, a phrase or a question, for instance QRM "I am being interfered with"!. Some 30 Q-codes are still used by amateur radio / morse code enthusiasts and the four below, plus QDM (the magnetic bearing to a station), still survive in aviation. For a full listing of Q-codes try www.cbug.org.uk/allqcodes.htm. The following four codes relate to altimeter settings.
QFE: the barometric pressure at the station location or aerodrome elevation datum point. If QFE is set on the altimeter pressure-setting scale while parked at an airfield, the instrument should read close to zero altitude – if the local pressure is close to the ISA standard for that elevation. However the use of QFE is deprecated and anyway, if the airfield elevation is higher than perhaps 3000 feet, older/cheaper altimeters may not be provided with sufficient sub-scale range to set QFE.
QFF: the mean sea level [msl] pressure derived from the barometric pressure at the station location by calculating the weight of an imaginary air column, extending from the location to sea level, assuming the temperature and relative humidity at the location are the long term monthly mean, the temperature lapse rate is ISA and the relative humidity lapse rate is zero. This is the Australian Bureau of Meteorology method; QFF calculations differ among meteorological organisations. QFF is the location value plotted on surface synoptic charts and is closer to reality than QNH, though it is only indirectly used in aviation.
QNH: the msl pressure derived from the barometric pressure at the station location by calculating the weight of an imaginary air column, extending from the location to sea level, assuming the temperature at the location is the ISA temperature for that elevation, the temperature lapse rate is ISA and the air is dry throughout the the column.
The Australian aviation regulations state that when an 'accurate' QNH is set on the pressure-setting scale at an airfield, the altimeter indication should read within 100 feet of the published airfield elevation, or 110 feet if elevation exceeds 3300 feet; otherwise the altimeter should be considered unserviceable. However due to the inherent inaccuracy possible in QNH, this may not be so. The difference between QFF and QNH when calculated on a hot day at a high airfield in Australia can be as much as 4 hPa, equivalent to about 120 feet. The advantage to aviation in using the less realistic QNH is that all aircraft altimeters in the area will be out by about the same amount, and thus maintain height interval separation.
The Local QNH at an airfield is normally derived from an actual pressure reading, but the Area QNH used outside the airfield zone is a forecast value, valid for three hours, and may vary by up to 5 hPa from any Local QNH in the same area. Either Local QNH or Area QNH may be set on the altimeter pressure-setting scale of all aircraft cruising in the Altimeter Setting Region; which [in Australia] extends from the surface to the Transition Altitude of 10 000 feet. The cruising levels within the Altimeter Setting Region are prefixed by 'A' e.g. A065 = 6500 feet amsl.
When there is no official Local QNH available at an airfield, and the site elevation is known, the Local QNH can be derived by setting the sub-scale (when the aircraft is on the ground of course) so that the altimeter indicates the known airfield elevation. The use of Local QNH is important when conducting operations at an airfield as the circuit and approach pattern is based on determining height above ground level [agl].
Note that it is not mandatory for VFR aircraft to use the area QNH whilst enroute. You may substitute the current local QNH of any aerodrome within 100 nm of the aircraft or the local QNH at the departure airfield. See 'Acquiring weather and QNH information in-flight'.
The purpose of the transition layer is to maintain a separation zone between the aircraft using QNH and those using the standard pressure setting. If Area QNH was 1030 hPa there would be about 500 feet difference displayed between setting that value and setting standard pressure. The transition layer extends from the Transition Altitude to the Transition Level which, in Australia, is usually at FL110 but it may extend to FL125 – depending on mean sea level pressure.
QNE: common usage accepts QNE as the ISA Standard Pressure setting of 1013.2 hPa. However another definition of QNE is the 'altitude displayed on the altimeter at touchdown with 1013 set on the altimeter sub-scale'. Also referred to as the 'landing altimeter setting'.
Within the latter meaning the term is only likely to be used when an extremely low QNH is outside an aircraft's altimeter sub-scale range, and the pilot requests aerodrome QNE from air traffic services. In Australia, such extreme atmospheric conditions are only likely to occur near the core of a tropical depression/cyclone and as QNE is not listed in the ICAO “Procedures for Air Navigation Services" air traffic services would not provide QNE on request.
However QNE can be calculated by deducting the QNH from 1013, multiplying the result by 27 [the appropriate pressure lapse rate per hPa] and adding the airfield elevation.
For example: QNH 960 hPa, airfield elevation 500 feet, pressure setting 1013.
QNE = 1013 –960 = 53 × 27 = 1431 + 500 =1931 feet [the reading at touchdown].


Remember Majuba!:suspect:

Well ive just this second completed a quiz for a major middle east carrier. The quastion was "what is QNH". the answer was " the local altimeter setting".
That'll do for me. Lets leave it there. Bloody Black magic

bushb... That's you back on the dole then...

Some may recall the days of the Civil Aviation Flying Unit.. and some of the chaps flying for it who thought they were someone special. One of them barked at a Glasgow controller one day: "What's the QNH" to which the reply given was: "It's the subscale setting on an altimeter such that the altimeter reads height above sea level on the surface of the airfield".

They don't make 'em like that nowadays.

well you should have seen the other two options.
a: brake energy
or
c : A london museum

When I worked up in the Shetlands (Oil boom - mid 80's) there were times when pressures were as low as 942mb. Most altimeters stop at 950mb