Do real pilots use QNH to mean altimiter setting?

But QDM (–.- -… --) is “bearing to” and QDR (–.- -… .-.) is “bearing from”.
These used to be common with RDF navigation in the Arctic.

Some random thoughts:

  1. Q codes were apparently started for Morse radiotelephony… and for some reason somehow stuck!
  2. It would seem that there is no logic to the letters used as far as any mere mortal can determine. So not an abbreviation, not an acronym, not anything logical.
  3. Between general communications, aviation and maritime uses, there are more than 200 Q codes (!).
  4. I used to fly in South Africa years ago. At that time there were a paltry few Q codes in regular use: QNH (as discussed), QFE (to show 0ft on the ground at X airfield), QSY (change frequency), QTR (what is the time), QBI (Instrument Flight Rules in effect at…). That was about it.
  5. Altimeter settings: as already mentioned just about the whole world uses the metric system. And in that regard: when I started flying in the 70’s, millibar was the norm in South Africa as the country was fully metricated. But some years later it was determined by the “General Conference on Weights and Measure” (which is globally recognised as the “governing body” for weights and measures) that the hectoPascal was the true SI metric unit of measure for pressure. And was thus formally accepted in aviation. Other than in North America…

And yes: in reality a hPa is exactly the same as a mbar.

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As mentioned several times, Q codes were originally for communication in Morse code. In Morse code, if the signal has a question mark (dit dit dah dah dit dit) after the code, it is a question. If not, it is a statement. So according to this archived NATO document the meanings are

QNH? What should I set on the sub-scale of my altimeter so that the instrument would indicate my elevation if I were on the ground at your station?

QNH If you set the sub-scale of your altimeter to read… millibars (or hundredths of an inch*), the instrument would indicate your elevation if you were on the ground at my station at…hours.
*Note: When the setting is given in hundredths of an inch the abbreviation “INS” is used to identify the units.

If you want something really obscure, there is the unofficial Q signal insult used among amateur radio operators. QLF? means “are you sending with your left foot?”


At my field in the UK yes, in fact we get both QNH and QFE. NH is used for leaving the airfield as this gives you height above sea level. QFE is provided/used when approaching the airfield and or when doing circuits. This gives you the height above the airfield.

I should add we don’t “request” either, we simply ask for “Airfield Information” and it is provided along with other useful bits such as wind strength and direction.

As for all the morse code stuff - who knows , I have a radio and altimeter.

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@willisxdc I started to give you a hard time about your morse code letter “D”, but then I realized the forum software changes . . to . . . :crazy_face: Can always tell the ham radio guys!


Didn’t notice that. Good thing I didn’t try writing the whole post in morse. Would be giberish.

Haha certainly, when I re-read another lengthy post of mine in a quotation I wondered how I would use so few punctuation marks. Then I realized I actually had used them but the software removed all commas and fullstops in the quotation.

A little OT, but while we’re on the subject…

The same’s true for saying “Roger” for “Received”. In wireless telegraphy days, “Received” very quickly got shortened to just the letter R. This carried over by tradition/habit to wireless telephony, and the phonetic alphabet for R in those days was “Roger”.

At what point in a flight do you set it back to 2992? Above 5000? 8000? or one you reach an FL?

Depends on the location, different countries have different transition altitudes. In the US it’s FL180, but it varies all over the world.


Just nitpicking now until the coffee starts to work :stuck_out_tongue: If you talk about transition ALTITUDE it’s 18000ft :stuck_out_tongue:

In Australia transition altitude is 10000ft. For all operations at or below transition altitude use local or area QNH. For cruise in the standard pressure region use 1013.2 hPa. (29.92) There is also a transition layer where:

FL125 navbl when area QNH is below 963 hPa
FL120 navbl when area QNH is below 980 hPa
FL115 navbl when area QNH is below 997 hPa
FL110 navbl when area QNH is below 1013 hPa

Cruising within the transition layer is not permitted.

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take it easy as that altimeter set (29.92 as standard value) is typical US system and HPa is rest of world where US system isn’t typical for use. Just one point, there is transition gap between transition altitude and transition level that do right things between going down through TL (reporting altitude on standard press QNH 1013 HPa) to altitude reporting on local airport QNH (down to approach airport) because logically local QNH can be higher than standard in some cases. You need to know airport QNH at t/o and app of airport to have all same altitude with other traffic +/- during procedure. Over specific altitude you set your altimeter gauge press to standard press (29.92 or 1013) and report FL no altitude. Sometimes is very important to hear ATC or traffic to understand because some aircraft can report f.ex. N67565 inbound LNZ 10000ft QNH1013 what points to standard press but no TL report so this aircraft is on QNH 1013 still at altitude reported and no on TL, it can point f.ex. to TMA transition with departure or arrival procedure. That TL is defined specifically from Country to Country but is logical that neighbored Countries have own specific DEP/ARR procedures of press set due maybe different requirements/rules about TL definition when aircraft comming/leaving it’s areas.

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