Acronym QNH

[DIA74]

Answer please.

This question has always been, for me, like one of those you don't ask the Doctor for fear it might make you look an idiot for not knowing the answer to already.

QNH is an acronym which refers, I believe, to pressure in mbs, but what do these letters actually stand for - Q.N.H. ??

[HEATHROW DIRECTOR]

I don't believe the letters mean anything. QNH is simple one of a long list of Q-codes..... QNH, QNE, QFE, QDM, QRM, QRA, QTH, et al.

[possibleconsequences]

DIA74,

HD is right, it doesn't stand for anything in particular, it comes from a long list of Q codes first used in morse signalling and adopted by various radio agencies etc since. There's a very good summary on wikipedia. Type in 'radio Q codes' in the wiki search and you'll get your answer.

[DIA74]

Thanks for your responses. I will check Wikipedia out.

[LogieBear]

Unsure on the Q. I believe this may relate to "Quotation" QNH would then stand for Quotation of Nautical Height, the height above sea level. Similarly, QFE is Field Elevation and the barometric height associated with an airfield.

[HEATHROW DIRECTOR]

LogieBear..... and QAI, QRM, QRN? This site is useful too:
Ralf D. Kloth DL4TA - List of Q-codes (http://www.kloth.net/radio/qcodes.php)

[champair79]

Question Nautical Height I believe.

[chevvron]

What the hell does 'Nautical Height' mean? Height expressed in nautical miles?

[99jolegg]

It doesn't stand for anything apparently - the term "nautical height" was tagged to it as a means of remembering the difference between QFE / QNH. I've also heard "field elevation" tagged to QFE. They're simply mnemonics rather than abbreviations.

Relevant section from Wikipedia (for what it's worth):

The abbreviation QNH originates from the days when voice modulated radio was often difficult to receive, and communication was done by Morse Code. To avoid the need for long Morse transmissions, many of the most commonly asked questions were incorporated into a Q code. When the operator sent the letter 'Q' it indicated that he had a question to ask. To ask for atmospheric pressure at sea-level (i.e., at zero altitude) the letters 'QNH' would be transmitted. A common mnemonic for QNH is "No Height", (whereas the mnemonic often used for QFE is "Field Elevation").

[Floppy Link]

QNP is when you get caught short and have to land in a field to go for a pee behind a bush.

[Robin Pilot]

As others have mentioned it goes back to the morse code days. It means "Question - Natural Height?". The answer would be the atmospheric pressure at sea level for the given time and location. So as an example, if airport x is reporting QNH 1007, then the atmospheric pressure at sea level, at the location of airport x, is 1007mb. The "pressure altitude" of that location can then be calculated with the temperature - which is useful for aircraft performance reasons.

QFE means "Question, Field Elevation?". Similar to QNH in that it is a measure of the air pressure, but setting this on the altimeter sub-scale would make the altimeter read an altitude of 0ft when sitting on the ground at the airfield it relates to. I believe this is more commonly used in the UK.

[HEATHROW DIRECTOR]

"Question Natural height" Strangely,I never had an aircraft say that to me when they didn't get the QNH right!! I think everyone on here knows what QNH means.

So, Robin, what's your interpretation of: QDM, QRM, QRA, QTH, QSK, QSS, QTC..?

[wings folded]

Pedantic mode on:

An acronym strictly speaking is a pronouncable word derived from the initial letters of a series of words, e.g. "scuba" or "laser".

When a series of initial letters produces something which is not pronouncable, it is an "initialism".

Unless I am much mistaken, you cannot that easily pronounce "QNH". At least, I can't.

So it is an initialism.

Might just stay in pedant mode for a while.

[FantomZorbin]

Pedant Mode ON: QNH refers to an Altitude (amsl), QFE refers to a Height above a specified datum (eg. airfield/touchdown elevation). It therefore looks as if "Nautical Height" was an attempt at some form of mnemonic which only served to confuse the issue further!
Pedant mode OFF.:E

FZ
S.O.D.C.A.T.

[HEATHROW DIRECTOR]

<<QNH refers to an Altitude (amsl), QFE refers to a Height above a specified datum >>

Not strictly correct. Both refer to altimeter settings which produce certain altitude/height readings. Very basically, if the QNH is set on an altimeter it reads aerodrome elevation, ie distance above sea level. Set QFE on an altimeter and it reads 0 (zero) on the airfield, although on some hilly airfields different QFE readings may be produced for different runways. There is a lot of good information here:

Altimetry in general explained | IVAO Academy (http://academy.ivao.aero/node/266)

[G SXTY]

And to quote my ATPL General Nav instructor (the legendary Baz):

“Q codes were invented by the military during the war to confuse the enemy, and they’ve been confusing the f*** out of pilots ever since.”

:D:D:D

[FantomZorbin]

HD
Yup, I agree with your comment but I thought that's what I implied. :O

Shall we confuse everyone with a discussion on QNE? :E

[wings folded]

Everybody might just QSY to a different thread.

[obnoxious]

QNH Nautical Height is Height, or level, above sea level, at mean tide (ASL) as in Hypsography using a levelling rod as in land surveying, or DGPS. It ia all in the Wiki

[Bullethead]

There are also 'Z' codes if you really want to confuse yourself.

Ralf D. Kloth DL4TA - List of Z-codes (http://www.kloth.net/radio/zcodes.php)

Not gunna mention the Falcon codes, oops already did! :}


Regards,
BH :8

[Been Accounting]

Query Newlyn Harbour ....

or Query Newlyn Height


Newlyn harbour is home to the NewLyn Tidal Observatory. This is the reference for "Mean Sea Level".

newlyn cornwall - Google Maps (http://maps.google.co.uk/maps?sourceid=navclient&hl=en-GB&rlz=1T4GGLL_enFR353FR353&q=newlyn%20cornwall&um=1&ie=UTF-8&sa=N&tab=wl)

File:Newlyn Tidal observatory Map 1946.png - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/File:Newlyn_Tidal_observatory_Map_1946.png)

[HEATHROW DIRECTOR]

<<QNH Nautical Height is Height, or level>>

But in aviation, height and level mean totally different things.

This thread is getting crazier!

[wings folded]

When I flew, I would frequently hear requests for the "Fox Echo", or be given the "Fox Echo" by ATC.

On the other hand, I do not recall ever hearing "November Hotel" being given nor requested.

In them days EGSH had an NDB labelled "NH", now decommissioned I gather.

Was this therefore just a local thing to avoid confusion?

Where is Niknak when we need him?

[BOAC]

We must not forget QGH, QDR and QTE, plus, of course, QFI, QHI and QTR (slightly slower than an OTR).

Dolphin, anyone?

[Hyperborean]

Not so sure about the Q being Question. If you go back to the basic morse procedure the codes were used with additional modifiers so that requests or questions could be indicated> For example QDL IMI meant "I request a series of bearings." QSL meant "I request an acknowledgment of my transmission." No "Question" implied in those cases. Also the initial coding could imply the request and the same coding would be used in the response. So sending QDM from a mobile station asked for a magnetic bearing; the ground station would then transmit QDM xxx for the relevant response.

[Capot]

QNH, as many have asserted, does not stand for anything.

It's just one of the many Q Codes; hang-over from key/Morse comms; since voice came into common use they are absolutely precise, well-understood shorthand and very useful too.

I can only recall a few apart from the ones still in use like QDM, whose opposite I've forgotten, QFE, etc.

As a learner in the '60s I learned the QDM cloudbreak/let-down/approach procedure, using bearings for one's transmissions reported by ATC as the sole reference for horizontal position. My little circular gizmo for that is still in my bag, but it was better to keep the vertical and horizontal situations in your head while flying it and not use the gizmo.

QGH was similar but controller-managed; you had to respond when he/she called and do exactly what you were told. Controllers would boast about how they could handle 6 simultaneously and not lose track of any of them.

[HEATHROW DIRECTOR]

<<QDM, whose opposite I've forgotten>>

QDM is Magnetic bearing to reach the station; QDR is your Magnetic bearing from the station.

[chevvron]

Back in '1970, in preparation for the move into Mediator Stage 1 at West Drayton, some of the 'crew chief designates' had to re-validate on LATCC radar sectors. A certain very senior controller caused some hilarity to us Radar Monitors (we updated the perspex edge-lit display boards for the radar controllers who were at Heathrow, with the 'D' controllers on the same frequency being at WD) by clearing a flight to route 'direct to XXX your Queen Dog Mike is ......!'

[FantomZorbin]

Aahem! ... I remember being told/taught that Mean Sea Level was measured at 2 different points in the UK, one of them being Newlyn and the other somewhere on the East coast.

If that is the case then is the Tyne Altimeter Setting Region (ASR) measured with respect to a different datum from that of Wessex ASR?:E

[Winglet__]

Not sure how true..... but have been told it's a hang over from the days of morse code abbreviations....

QNH = Question Nil Height
QFE = Question Field Elevation

Set QNH and your altimeter reads height above sea level - pressure setting to correct altimeter to Nil Height datum(sea level).

Set QFE and your altimeter reads zero at the aerodrome that it's accurate for - pressure setting to correct altimeter to field elevation datum.

[Capot]

.. is the Tyne Altimeter Setting Region (ASR) measured with respect to a different datum from that of Wessex ASR?

The QNH is the ambient pressure for each altimeter setting region adjusted to equivalent at Mean Sea Level, he says dredging back 40++ years.

It's what you set on your altimeter as the MSL pressure when you enter a new ASR, so as to have a fighting chance of not hitting a hill, and if landing in that ASR on QNH and not QFE, of hitting the runway when you expect that to happen.

So the answer to your question is "no". The MSL datum used is the same, regardless of which ASR you are in.

Unless an expert knows better.....

[Cornish Jack]

Hyperborean is nearest to being correct.
The 'Q' was NOTHING to do with questioning. It was just a common starting letter for a variety of shorthand codings for various bits of aeronautical information. If it was used to request information, it was followed by the suffix IMI - those three characters sent as one, NOT separated. It was the civilian version of a similar range of codes for military use which were preceded by 'Z' - cannot now remember any examples but, for 'Z' codes, the interrogative was INT - also sent as a single character.
The various "Newlyn Harbour", Field Elevation" etc., were simply various people's attempts to provide aide memoires for the meanings.

[folkyphil]

Am in total agreement with Cornish Jack and Hyperborean on this issue.

As an aside, the NOTAM Codes (introduced to provide consistent dissemination of aeronautical data) also begin with "Q";..no "question" about that...

[Robin Pilot]

No idea about the other codes HD, just repeating what I've read in texts. Was trying to be helpful in a spotters thread where maybe everyone doesn't know what QNH means. I could have articulated a little better I admit :), but then I'm not a lecturer.

I usually don't bother, but having read responses saying "it doesn't mean anything" I felt obliged.

FWIW - I've also read "Question Nil Height" (as mentioned by Winglet) in other texts.

[IRRenewal]

It's neither an abbreviation nor an acronym. It's a code.

This website (already mentioned for the z codes) Ralf D. Kloth DL4TA - List of Q-codes (http://www.kloth.net/radio/qcodes.php) gives a good overview of meaning, use and history of Q codes.

An aircraft would request QNH? to which the reply would be QNH1030 or QNH2992INS.

Ps: Since the 'Q' is used in both the question and the reply, it can definitely not mean 'question'.

..._._

[ricardian]

See ACP131 (Operating Signals) (http://jcs.dtic.mil/j6/cceb/acps/acp131/ACP131F.pdf) for a full list of Q and Z codes.