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As the VOR frequency is automatically selected when the DME is selected, under what system conditions is manual tuning of the VOR required?

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(aviation-safety-bureau.com)

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    $\begingroup$ "As the VOR frequency is automatically selected when the DME" Not in my plane it isn't, unless you are talking about the DME being colocated with the VOR. There are many VOR's to choose from, not all of which have DME. You need to choose the frequency of the one you want to navigate based on. $\endgroup$ – Ron Beyer Jan 19 '17 at 18:34
  • $\begingroup$ How is manual tuning of a VOR can be carried out from the aircraft VHF NAV control panel ? $\endgroup$ – Al Yaqdhan Jan 19 '17 at 18:39
  • $\begingroup$ On my aircraft you either use a knob on the NAV radio to select the standby frequency then hit the "flip-flop" button to move it over to active, or I have a Garmin G430W which I can tune NAV1 by selecting a menu and VOR then hitting the flip-flop button. This is pretty typical in most aircraft. $\endgroup$ – Ron Beyer Jan 19 '17 at 18:41
  • $\begingroup$ Sir it seems to me that you are flying small aircraft, what about a320 how would you tune the VOR ? $\endgroup$ – Al Yaqdhan Jan 19 '17 at 18:57
  • $\begingroup$ "when the DME is selected". This sounds confusing to me.Where do you select the DME exactelly ? $\endgroup$ – Radu094 Jan 19 '17 at 19:09
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As pointed out in the comments, I think you have things turned around. If you select the frequency of a VOR that has a co-located DME, the system will automatically also select the DME frequency. Thus, I'm guessing that what you perhaps meant to ask is under what conditions do you manually tune the DME frequency. If that is NOT what you are asking, put a comment after this answer to that effect, and I will delete this answer.

Now, if that is what you are asking, the answer in one sense is "never" in that, at least in civilian aircraft, you always select the VOR frequency. However, prior to my retirement in 1999 there were a few, very few as I remember, facilities that provided DME but at which there was no co-located VOR. To get the DME, you selected the VOR frequency that would have been paired with the DME had there been a co-located VOR. and it was the frequency of that non-existent VOR that was shown on the charts along with a clear and obvious note that there was no actual VOR. I have no idea whether in our current airspace system such still facilities exist.

You can find the standard VOR-DME frequency pairings here (PDF) or read about it on Wikipedia.

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  • $\begingroup$ HLE NDB / DME has a collocated NDB and DME. There is no VOR. There are several NDB / DME stations around. One reason to tune the DME without an operational localizer / VOR. skyvector.com/… $\endgroup$ – wbeard52 Jan 19 '17 at 22:15
  • $\begingroup$ I take it ILS/DME pairings work like their VOR/DME brethren? $\endgroup$ – UnrecognizedFallingObject Jan 19 '17 at 23:14
  • $\begingroup$ @UnrecognizedFallingObject, yes. The same receiver is used for both ILS and VOR (though the decoding is different) and the pairing works the same. $\endgroup$ – Jan Hudec Jan 20 '17 at 20:56

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