Loading a DME Fix on ATC Clearance

[Txbyker]

How do you best load a DME fix on a clearance when the fix is not on any charts as a way point and is truly a point along a VOR radial?  I am often given a clearance to fly to the 30 mile DME fix on the 321 degree ADM VOR radial for example.  I take too long to try to figure out how to load it in my Garmin G1000 and instead just hand fly the darn thing.  Foreflight does a good job of loading it as ADM/321/030 but not so for our GPS that I am aware.

Russ

[Robert C.]

Well, this may be more work than it’s worth:

1) got to WPT page #5

2) select “new wpt” soft key

3) name the wpt (e.g. DME fix)

4) in the “reference waypoint” window you should now be able to enter the VOR, radial and distance 

5) back to FPL page and insert the DME fix as you would with any new waypoint.

have never tried it but is the only way I can think of doing it.

Robert

[Mooneymite]

....or just ask for a vector.  

[Bob - S50]

48 minutes ago, Robert C. said:

Well, this may be more work than it’s worth:

1) got to WPT page #5

2) select “new wpt” soft key

3) name the wpt (e.g. DME fix)

4) in the “reference waypoint” window you should now be able to enter the VOR, radial and distance 

5) back to FPL page and insert the DME fix as you would with any new waypoint.

have never tried it but is the only way I can think of doing it.

Robert

I cannot think of a better way, but I've noticed when I do that with the GTN simulator, the fix does not end up on the correct radial.  That's because the GPS calculates magnetic variation and could be a couple degrees different than that used by the VOR.  Granted, if it is off by 2 degrees and you are going to the 30 mile fix you'll only miss the fix by a mile, but the engineer in me wants it to lie on the radial.  I might warn the controller that because of the way the GPS works, I might miss the fix by a mile or two and see what they say.

In my case, I'd probably just enter it into my KNS80 and use that to fly to the fix.

[jaylw314]

10 minutes ago, Bob - S50 said:

I cannot think of a better way, but I've noticed when I do that with the GTN simulator, the fix does not end up on the correct radial.  That's because the GPS calculates magnetic variation and could be a couple degrees different than that used by the VOR.  Granted, if it is off by 2 degrees and you are going to the 30 mile fix you'll only miss the fix by a mile, but the engineer in me wants it to lie on the radial.  I might warn the controller that because of the way the GPS works, I might miss the fix by a mile or two and see what they say.

In my case, I'd probably just enter it into my KNS80 and use that to fly to the fix.

According to Rod Machado's IFR training series, the VOR radials and GPS tracks should be consistent.  While magnetic variation affects the VOR radials, the maps also take into account inaccuracy in the VOR transmitters as well.  The end result is that if you plot a radial from a VOR on GPS, it should be consistent with that same radial on a map.

That being said, why not press the OBS button on Garmin equipment, dial in the radial, and track that radial out to the DME distance?  When ATC wants you to fly to a DME fix, that's usually what they expect to happen, right?

Edit: Oh, now I see what you're saying.  The maps take into account inaccuracy in the VOR transmitter, but the GPS does not, so the fix could be off by how much the transmitters are allowed to be off (+/- 1.4 deg)

Edited December 5, 2017 by jaylw314

[midlifeflyer]

40 minutes ago, jaylw314 said:

According to Rod Machado's IFR training series, the VOR radials and GPS tracks should be consistent.  While magnetic variation affects the VOR radials, the maps also take into account inaccuracy in the VOR transmitters as well.  The end result is that if you plot a radial from a VOR on GPS, it should be consistent with that same radial on a map.

That being said, why not press the OBS button on Garmin equipment, dial in the radial, and track that radial out to the DME distance?  When ATC wants you to fly to a DME fix, that's usually what they expect to happen, right?

Edit: Oh, now I see what you're saying.  The maps take into account inaccuracy in the VOR transmitter, but the GPS does not, so the fix could be off by how much the transmitters are allowed to be off (+/- 1.4 deg)

Also consider how much your VOR equipment is allowed to be off and still usable.

[Bob - S50]

18 hours ago, jaylw314 said:

According to Rod Machado's IFR training series, the VOR radials and GPS tracks should be consistent.  While magnetic variation affects the VOR radials, the maps also take into account inaccuracy in the VOR transmitters as well.  The end result is that if you plot a radial from a VOR on GPS, it should be consistent with that same radial on a map.

That being said, why not press the OBS button on Garmin equipment, dial in the radial, and track that radial out to the DME distance?  When ATC wants you to fly to a DME fix, that's usually what they expect to happen, right?

Edit: Oh, now I see what you're saying.  The maps take into account inaccuracy in the VOR transmitter, but the GPS does not, so the fix could be off by how much the transmitters are allowed to be off (+/- 1.4 deg)

And I think Rod was talking about airways, not radials.  That is, if there is an airway from a VOR to an intersection let's assume it uses the 180 degree radial.  Your GPS may tell you the desired track is 182.  Even dialing in the 182 course will take you to that intersection because the GPS is calculating a great circle route to a lat/long coordinate.  So even though the selected course is different, the track will be the same.  On the other hand, if you were to enter a manual waypoint, YOU are supplying the coordinates for the GPS to steer to.

Try it next time you fly.  Pick an intersection on an airway.  Look on the low chart and find the radial and DME for that fix.  Then create a new named waypoint using that radial/DME.  Then look at the map page and see if your new waypoint lies on top of the intersection or off to the side.  I'm guessing the error will be greatest if you live in the NE or NW part of the country where magnetic variation is greatest.  If you live in the heartland of America it probably will be pretty close.

[jaylw314]

Yes, I realized that halfway through my post.  I suppose the only comfort is that with your VOR receiver allowed a +/- 4 deg error, fixes off a VOR by definition do not imply a lot of precision...