QDM QDM QDM Request QDM

On July 10, 2010, in Aircraft Guides, Safety, by admin

Have you ever wondered what all that nonsense about QNH, QFE, QTM and so on are all about?  I certainly did and I used to ask my pilot friends regularly. I was still a student then, but nobody answered me. I thought perhaps that QFE might stand for “Question for Field Elevation” and QNH might be “Question for Nautical Height” or some such nonsense. It turns out the real story is more random and less complicated. In 1912 in London the Q-Codes were created by the Radiotelegraphy Convention. For Aviation the range QAA-QNZ had been allocated, although the range QRA-QUZ are available to all stations. The ICAO then assigned meaning to many Q-Codes, presumably so that communication could be more effiicient.

However you should not use Q-Codes which are so obscure that the receiving station does not know what they mean. For example if you received:
Golf Alpha Bravo Charlie Delta Request sea level QAH and QAK
You response might be:
2 Thousand feet. Negative. Request QAU.
Luckliy as pilots we only need to remember a few Q-Codes and their meaning.
Aviation Specific
QDM – Magnetic heading to steer towards you with no wind.
QDR – What is the magnetic bearing from you
QFE – Subscale setting to indicate height above your airfield
QNH – Subscale setting to get the field elevation if I were on the ground at your airfield.
All Stations
QTE – My true bearing from you
QTM – What is your magnetic bearing.
The Q-Codes relating to bearing are sometimes used as examples for Instrument training tracking towards or from stations but these are rarely if ever heard these days.
By the way QAH is requesting a height, QAK is asking if there is a risk of collision and QAU is requesting where the fuel should be jettisoned.
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