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. Although wireless telegraphy in aviation is virtually non-existent these days (c.2006) the Q code still exists and is contained in ICAO PANS (Procedures for Air Navigation Services) Doc 8400 : The ICAO Q Code.
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:
p/s This article was forwarded to me by 9W2TZ...
Tnks for sharing Hanafi...
ICAO means International Civil Aviation Organization