The
Q code was instituted at the Radiotelegraph Convention held in London in 1912
as a means of creating a 'shorthand' for use with Morse code. At that time, the
Q code was intended for use by shipping. The code consists of a large number of
three-letter groups beginning with 'Q', of which the groups QAA to QNZ were later
reserved for the aeronautical service.
When radio was introduced to civil aviation in the early 1930s all radio communication was by wireless telegraphy (W/T). It should be noted that this included aeronautical point-to-point, as well as air-ground services.
Each code group had a specific meaning assigned which remained the same regardless of the language spoken by either operator, thus neatly overcoming the problem of communications on international services (the later move to voice communication by HF and VHF radio-telephone necessitated the adoption of English as the international language of aviation).
Each code group
is either a question, an answer or an intention depending on the direction of
the communication. For example, QAA is the first code group in the aeronautical
section. As a question from the ground station to the aircraft, QAA means "At
what time do you expect to arrive?" As an answer, or as a statement of intention
from the aircraft to the ground station, QAA means "I expect to arrive at...".
Numerals and other qualifiers could be added to the basic Q groups as required. Thus "QAA 1500" means "I expect to arrive at 15.00 hours". Examples of qualifiers included units of measurement such as FT (feet), ML (miles), MPH (miles per hour) and whether the aircraft was climbing (ASC) or descending (DES). Location indicators could also be used: for example, VML was the indicator for Melbourne.
An example of a W/T message using the Q code is given in Flying Empires: Short 'C' Class Empire Flying Boats by Brian Cassidy:
GJX GJX DE GADHL GADHL GADHL - GM - TEST - QRK - QSA - K
(Eastleigh from G-ADHL - Good morning - Testing - Do you receive me well? - Are my signals good? What is the strength of my signals? - Please reply)
The reply would be as follows:
GHL GHL GHL DE GJX - GM - QRK - QSA 5 - K
(G-ADHL [abbreviated] from Eastleigh - Good morning - Receiving you well - The strength of your signal is 5 - Reply)
The aeronautical part of the Q-code was, for British (including Australian) users, originally contained in Air Publication 1529 The 'Q' Code and Other Abbreviations to be Used in the Civil Aeronautical Radio Service. The Q Code was removed from ICAO PANS (Procedures for Air Navigation Services) Doc 8400 in 1999.
A few remnants of the Q code survive in speech communications. For example, QNH is used to refer to the altimeter pressure setting that would show elevation above sea level if the aircraft were on the ground at that location.
Some
selected examples of Q code groups are given below to illustrate the breadth of
the contingencies covered by the code. Frankly, the mind boggles in an attempt
to imagine situations where some of these groups would find a use:
| Q code | Question | Answer or Advice |
| QAB | May I have clearance (for ...) from ... (place) to ... (place) at flight level/altitude ... ? | You are cleared (or ... is cleared) by ... from ... (place) to ... (place) at flight level/altitude ... |
| QAU | Where may I jettison fuel? | I am about to jettison fuel. or Jettison fuel in ... (area). |
| QBF | Are you flying in cloud? | I am flying in cloud at ... flight level/altitude ... [and I am ascending (descending) to flight level/altitude ...]. |
| QCH | May I taxi to ... (place)? | Cleared to taxi to ... (place). |
| QDM | Will you indicate the MAGNETIC heading for me to steer towards you (or ...) with no wind? | The MAGNETIC heading for you to steer to reach me (or ...) with no wind was ... degrees (at ... hours). |
| QEF | Have I reached my parking area? or Have you reached your parking area? | You have reached your parking area. or I have reached my parking area. |
| QFU | What is the magnetic direction (or number) of the runway to be used? | The magnetic direction (or number) of the runway to be used is ... Note.- The runway number is indicated by a two-figure group and the magnetic direction by a three-figure group. |
| QGH | May I land using ... (procedure or facility)? | You may land using ... (procedure or facility). |
| QKC | The sea conditions (at ... position) ... 1) permit alighting but not take-off. 2) render alighting extremely hazardous. | |
| QMI | Report the vertical distribution of cloud [at ... (position or zone)] as observed from your aircraft. | The vertical distribution of cloud as observed from my aircraft at ... hours at ... (position or zone) is : lowest layer observed* ... eighths (... type) with base of ... (figures and units) and tops of ... (figures and units) [*and similarly in sequence for each of the layers observed.] height above ... (datum). |
| 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). |
| QNH | What should I set on the subscale of my altimeter so that the instrument would indicate its elevation if my aircraft were on the ground at your station? | If you set the subscale of your altimeter to read ... millibars, the instrument would indicate its elevation if your aircraft were on the ground at my station at ... hours. Note.- When the setting is given in hundredths of inch the abbreviation INS is used to identify the units. |
| QNI | Between what heights above ... (datum) has turbulence been observed at ... (position or zone)? | Turblence has been observed at ... (position or zone) with an intensity of ... between ... (figures and units) and ... (figures and units) heights above ... (datum). |
| QNO | I am not equipped to give the information (or provide the facility) requested. |
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