In the aviation community (at least outside North America), the terms QNE, QNH, and QFE are used to describe standard pressure, local altimeter, and field elevation, respectively.

But what is the origin of the "Q" code names?


QNE, QNH, and QFE are Q Codes - the Q Codes are designed for telegraph (or radiotelegraph) use where information is transmitted in morse code and brevity is essential (e.g. "QNH KJFK 2992 INS" is much shorter to tap out in morse code than "JFK Altimeter 29.92 inches of mercury")

They are still used in verbal communication (radiotelephone), though much less frequently.
ICAO defines a list of standard Q codes for use in aviation (this site has a list).

Regarding the choice of Q as the prefix for these codes, this is to avoid confusion with station callsigns. The ITU currently will not assign prefixes beginning with Q to any country.
(There may be further historical reasons behind the choice of "Q", but I'm not aware of any.)

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    $\begingroup$ "Q" is not a common letter in many languages (the Germans used it as space when encrypting with enigma, which didn't have a space) $\endgroup$ – ratchet freak Jun 26 '14 at 11:19
  • $\begingroup$ @ratchetfreak That probably plays into the decision to use it as well -- Q isn't the thinnest part of the English dictionary, but it's also certainly not a commonly-used letter here either. $\endgroup$ – voretaq7 Jun 26 '14 at 18:42

One of my PPL textbooks briefly discussed the origins of QNH. Unfortunately I can't for the life of me find the correct passage, so I am unable to reference this properly. But from memory:

It dates back to the early days of navigation when the main communication method was morse code through the radiotelegraph. The aircraft, wanting the atmospheric pressure for altimiter calibration, would basically ask the ground station "I have a question - what is the atmospheric pressure at normal height?" The 'normal height' reference over time became the sea level reference that we use today.

So, because this question was so frequently required - and therefore an awful lot to communicate through morse code - it was abbreviated. "I have a question" became Q, "what is the pressure at normal height?" became NH - the message transmitted therefore was simply QNH.

I presume the other Q codes evolved in a similar manner.

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    $\begingroup$ That sounds a lot like a back-formation, to me. (I.e., "We have this pre-existing code, QNH. Can anyone think of anything it could stand for, so it's easier for people to remember?") $\endgroup$ – David Richerby Nov 21 '14 at 14:28
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    $\begingroup$ Q-codes can be questions or statements. Certain Q codes only make sense as one or the other, not both, whereas many can be used as both statements ("QTH SPRINGFIELD" meaning "my location is Springfield") and questions ("QTH?" meaning "what is your location?"). Also consider for example "QSL" meaning "I confirm receipt of your transmission" whereas "QSL?" means "please confirm receipt of my transmission". (With reservation for the exact literal meaning.) $\endgroup$ – a CVn Nov 21 '14 at 14:59
  • $\begingroup$ I agree with David Richerby. Without having a reference for this Q-code origin, I believe this statement is a back formation. I will look forward to being proved wrong, however.... $\endgroup$ – Skip Miller Nov 22 '14 at 17:21

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