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Thread: S.O.S - Q.D.M, question/answer ?

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    Default S.O.S - Q.D.M, question/answer ?

    Hello,

    Here is the mission statement of 425 Sqdn dated 7 December 1942 (Mission Mannheim). The Wellington III. BJ657, launches S.O.S. Q.D.M. 0060X 0020 hrs.
    I want to know when was the last position of Wellington when the browser launched its S.O.S.Q.D.M. There's coordinates 0060X ?
    Cordialement,
    Regards,
    Mit freundlichem Gruß,

    Dan

    Association Bretonne du Souvenir Aérien 39-45
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    QDM = 'what is the magnetic course to reach you with zero wind?' It's a course, not a co-ordinate.

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    The calculation must be complicated to achieve ?
    Cordialement,
    Regards,
    Mit freundlichem Gruß,

    Dan

    Association Bretonne du Souvenir Aérien 39-45
    http://www.absa3945.com/

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    When did the Darkie (or Darky, or Darkey) system of emergency radio nav bearings for aircraft in distress come into being? And what was its range?
    HTH
    Peter Davies
    Last edited by Resmoroh; 25th July 2015 at 10:34. Reason: QSD
    Meteorology is a science; good meteorology is an art!
    We might not know - but we might know who does!

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    Quote Originally Posted by Resmoroh View Post
    And what was its range?
    HTH
    Peter Davies
    Don't know when the Darky system started, but it used R/T (voice) so range was limited to around 10 miles. Hence locations could be given in clear. FWIW, a pilot's and W/Op's handbook from 1941 refers to the 'emergency R/T Organisation' and doesn't call it 'Darky'.

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    Default S.O.S - Q.D.M, question/answer ?

    Hello Dan

    When you refer to the Wellington “launches S.O.S. Q.D.M.”, I believe that the aircraft is initiating or sending the SOS QDM. Richard has answered the QDM generally in his post #2.

    However, having looked at my Air Ministry copy of “The ‘Q’ Code” (AP 1529 2nd Edition, June 1937 extract below) and your question, as to whether it is the S.O.S. Q.D.M., Question or Answer.

    Referring to “The ‘Q’ Code”, I believe the QDM will fall under QDM “Answer or advice.” In other words the aircraft is advising (sending) the QDM.

    A QDM will not give you a 'fix'.

    If the wireless station that the aircraft used (to take his QDM bearing), is known, then you should be able to draw a line and the aircraft was somewhere along that line approximately.

    Only one or two wireless stations taking a bearing of the aircraft SOS transmission, plus the Master Station taking a bearing and plotting the other bearings along with their own bearing (2 or 3 bearings in total) of the aircraft SOS, can a D/F 'fix' of the aircraft be established.

    Mark

    Last edited by Mark Hood; 25th July 2015 at 18:15.

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    Hi Mark - not sure that's quite right. I think the sense QDM is used in is best represented by the definition in AP1751 'Blind Approach Handbook' - 'What is the magnetic course to steer with zero wind to reach you?' It is asking the ground station to fix the aircraft (who is the most likely of the two to be lost) and give them a homing. The thing with Q Code is it is both question and answer (QDM from a/c = 'what is course to steer...', QDM from ground station = 'your course to steer is ...')
    HTH,
    Richard

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    Hello Richard

    According to Bill Chorley all the aircraft crew are on the Runnymede Memorial.

    Looking at Dan's statement, it is the aircraft that "launches S.O.S. Q.D.M." with degrees and a time.

    If the aircraft is losing height and it is doubtful whether there might be enough time for several ground/UK wireless stations to take D/F bearings of the aircraft in distress and plot them, to get a cut (where the bearings intersect) to 'fix' the position of the aircraft in distress, before it goes down. The Wireless Operator of the aircraft in distress can tap out an SOS QDM with the bearing he has taken, of the ground/UK Wireless Station and the time.

    When an aircraft wants a directional course to steer to reach his Station HF D/F, the aircraft usually requests a QDM and the receiving Wireless Station gives QDM and the number in degrees to the aircraft, for the aircraft to steer.

    However, an 'SOS QDM' with the number in degrees and a time, launched by the aircraft, is a reversal of the preceding sentence/paragraph above. The aircraft Wireless Op is giving the QDM, a bearing he has taken of the ground/UK wireless station which he is working, along with the time, pre-fixed by SOS.

    The SOS QDM from the aircraft in distress is saying ... Save Our Souls 'The magnetic course to steer with zero wind, to reach me is' with degrees and a time. So the UK Wireless Station is being advised of a directional bearing toward the SOS aircraft, should a Rescue Search be attempted.

    The Q Code, extract post 6, indicates the QDM can be sent from the ground wireless station to the aircraft, or in this case, vice versa.

    Mark
    Last edited by Mark Hood; 26th July 2015 at 07:27.

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    Hi Mark - thanks for the explanation, that makes eminent sense! I've spent a bit of time recently swatting up on D/F homing etc, but hadn't spotted that variation!

    cheers,

    Richard

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    Strictly speaking (although the W/T experts will correct me if I'm wrong) if the Tx Sta issues a Q-Code it is a statement from the Tx Sta to the Rx Sta. If the Tx Sta is asking a question of the Rx Sta then the signal should be "QDM IMI" (where 'IMI' is the Morse interrogative, or question-mark). However, the transmission of "SOS QDM . . ." by the a/c would appear to supercede the normal procedures - as has been demonstrated. The last thing the WOP would do before leaving his position in order to bale out would be to screw the brass key down (with the transmitter 'on') so that even though the a/c may have been 'empty', and if the engines/generators were turning, it would give the land-based D/F stations a chance to get as good a bearing as possible before the signal faded/stopped so that they could give the ASR boys as good a position to start looking as possible!
    Nowadays, we can't move anywhere without 100 systems knowing where we are. But in those WW2 days it was often a matter of life or (more often, regretfully) death. We are lucky
    HTH
    Peter Davies
    Meteorology is a science; good meteorology is an art!
    We might not know - but we might know who does!

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