GNS530W Radio Navigation Question

[Cody Stallings]

Curious.

Under the VLOC Frequency window on the 530W there is a third window that can have Traffic or the VOR info your tracking.

In that window, the Distance To said VOR, is that DME distance or GPS Distance?

Thanks in advance.

[kortopates]

Curious.
Under the VLOC Frequency window on the 530W there is a third window that can have Traffic or the VOR info your tracking.
In that window, the Distance To said VOR, is that DME distance or GPS Distance?
Thanks in advance.

GPS distance, after all it's a GPS.
There isn't also a DME in the box.


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[carusoam]

Great question...

I have forgotten, or didn’t know exactly how DME actually determines distance... other than straight line, to the station from altitude.

GPS systems don’t use the DME technology...

The all in one boxes use the actual VOR and ILS for some types of approaches... and GPS for the rest...

Yet, no DME...

But then again, the FAA has made DME less and less important as it is slowly phasing away...

PP thoughts only, not a CFI...

Let me know if I have missed something with this import nav equipment question...

Best regards,

-a-

[McMooney]

my understanding, they are actually going to add dme's back to the system.

https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/transition_programs/nextgen_dme/

 

[carusoam]

Bummer... the modern world will still need a good plan B... go DME... 

Last time we needed good plan Bs.... we were not allowed to fly... 9/11...

Best regards,

-a-

[Cody Stallings]

33 minutes ago, kortopates said:

GPS distance, after all it's a GPS.
There isn't also a DME in the box.


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Okay, so when it’s giving you a radial To Or From the station an distance, that’s all GPS based. The Actual VOR isn’t doing the communication to the box?

So if a VOR is turned off for whatever reason, the 530 will still track it because it’s just a Fix?

[kortopates]

39 minutes ago, Cody Stallings said:

Okay, so when it’s giving you a radial To Or From the station an distance, that’s all GPS based. The Actual VOR isn’t doing the communication to the box?

So if a VOR is turned off for whatever reason, the 530 will still track it because it’s just a Fix?

The 530W doesn't do anything internally with the VOR signal other than identify the station. It merely passes the signal to an external CDI. If the VOR is the active waypoint and you have it LOC mode, the internal nav information being displayed (distance, left/right of DTK, time to station etc) is all based on GPS data. The LOC button merely controls what is passed to the external CDI or HSI. The VOR is just database waypoint. If the VOR is out of service, you can still navigate enroute using GPS. You won't be affected by a down VOR until it defines the final approach path of a VOR approach, since we can not substitute GPS for a VOR approach unless we can also monitor the raw VOR nav signal while using GPS (think bearing pointer or second CDI turned to VOR, then you can keep the box in GPS mode on a VOR approach). But if the VOR is required for the missed approach, then we can use RNAV to substitute for the down VOR and still fly the approach, but ATC will also have a documented missed approach fix that can be used on a VOR or ILS approach to keep the approach available for the non-rnav users.
Did that answer your questions? 

Edited July 17, 2019 by kortopates

[kortopates]

2 hours ago, McMooney said:

my understanding, they are actually going to add dme's back to the system.

https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/transition_programs/nextgen_dme/

 

I don't think its as much adding DME back as it is incorporating DME in our new PBN RNAV requirements. The truth is the FAA still has no clue what they are going to do strategically for a GPS backup. They're looking at everything imaginable including talking about the old Loran. I am just hoping they come up with something that uses the same spectrum as GPS that might be compatible with our existing expensive GPS's with new software, rather than new hardware. But I am sure that is pure fantasy wish on my part. 

Edited July 17, 2019 by kortopates

[Ragsf15e]

As others said, the distance displayed in the GPS is only based off the Gps.  It doesn’t have a DME system in the box, only gps.  

Heres a couple additional tidbits... if you did have a separate DME and it was tuned to the same VORTAC or VOR/DME (VOR by itself doesn’t have DME), the displayed distance wouldn’t always match exactly.  DME measurements are line of sight, so altitude affects the calculation as you get closer to the station.  If you pass over at 12,000’, it will show 2nm where the gps will show 0.

Also, the Gps can give you a radial from/to the station based off the gps waypoint for the station if it’s in gps mode.  It can also give you radial to/from with the raw data in vloc mode by passing the raw data to your cdi.  Those will also be slightly different due to some issues with VOR magnetic deviation.

The faa has determined that we can substitute the gps for all the VOR information except for monitoring the final approach portion as Korpates said - even with the minor differences.

Edited July 17, 2019 by Ragsf15e

[jaylw314]

14 hours ago, Cody Stallings said:

Okay, so when it’s giving you a radial To Or From the station an distance, that’s all GPS based. The Actual VOR isn’t doing the communication to the box?

So if a VOR is turned off for whatever reason, the 530 will still track it because it’s just a Fix?

Not to "dogpile on the wabbit" , but remember that DME info is transmitted on frequencies that are close to UHF, so it requires a separate antenna and receiver from the VOR receiver (which transmits its info over VHF ranges).  The 530 doesn't have any input for reception in that frequency range AFAIK

[kortopates]

As others said, the distance displayed in the GPS is only based off the Gps.  It doesn’t have a DME system in the box, only gps.  
Heres a couple additional tidbits... if you did have a separate DME and it was tuned to the same VORTAC or VOR/DME (VOR by itself doesn’t have DME), the displayed distance wouldn’t always match exactly.  DME measurements are line of sight, so altitude affects the calculation as you get closer to the station.  If you pass over at 12,000’, it will show 2nm where the gps will show 0.
Also, the Gps can give you a radial from/to the station based off the gps waypoint for the station if it’s in gps mode.  It can also give you radial to/from with the raw data in vloc mode by passing the raw data to your cdi.  Those will also be slightly different due to some issues with VOR magnetic deviation.
The faa has determined that we can substitute the gps for all the VOR information except for monitoring the final approach portion as Korpates said - even with the minor differences.

Very good points.
Differences in magnetic variation are very real, typically the VORs will be different by at least a degree or more for good reason unfortunately. This translates in being careful when using OBS mode as we could be a ways off. But this issue is eliminated by flying a leg rather than using OBS mode at significant distance away from a VOR.
But difference in DME becomes indiscernible at approach altitudes where it becomes important. Why? - basic trig shows difference is less than 0.1 NM. But at enroute altitudes we really don't care about the difference; especially crossing a VOR which is went we see the max difference. In fact GPS is then giving us the accurate distance.


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[jaylw314]

21 minutes ago, kortopates said:

Very good points.
Differences in magnetic variation are very real, typically the VORs will be different by at least a degree or more for good reason unfortunately. This translates in being careful when using OBS mode as we could be a ways off. But this issue is eliminated by flying a leg rather than using OBS mode at significant distance away from a VOR.
But difference in DME becomes indiscernible at approach altitudes where it becomes important. Why? - basic trig shows difference is less than 0.1 NM. But at enroute altitudes we really don't care about the difference; especially crossing a VOR which is went we see the max difference. In fact GPS is then giving us the accurate distance.


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That error is probably the most significant when you're given non-published hold instructions from ATC, e.g. "hold on the 270 radial from the VOR at 25 nm DME".  Since you're not flying point to point, you don't have a leg to fly.

[kortopates]

That error is probably the most significant when you're given non-published hold instructions from ATC, e.g. "hold on the 270 radial from the VOR at 25 nm DME".  Since you're not flying point to point, you don't have a leg to fly.

Sort of us, but not really. Today whether you are RNAV or not, ATC will assume you are and the old ground based nav holding instructions aren't used unless you ask. So like your example, instead of being told to "hold west on the 9 DME 83 degree radial..." you'll hear hold west of VISTA...". You'll virtually always be given a RNAV waypoint to hold on, eliminating any concern for these differences. But if you got such and an old style, I would be looking at the enroute chart for the waypoint name and use that.

But where it's important, and about the only real practical example I can offer, is in departure clearances that are not in the database. These can involve intercepting and flying a radial to an waypoint or VOR that is ways away from the VOR. For these you'll want to take advantage of OBS mode for it's ease and effeciency, but if the distance away from the VOR is great and variation differences are too (easily looked up) we need to be aware of consequences of the variation differences and sometimes go to the trouble of defining legs in the flight plan to eliminate such error when that significant. It's generally not that significant till you are going by class Bravo airport's traffic flows.


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[Steve W]

One thing to note is that if the active waypoint is a VOR many devices will give the VOR corrected radials in OBS mode(even with a GPS source) but if the waypoint is a fix then you'll get current variation.

i.e. in the GTN 750 trainer

UBG to GLARA shows 091(local current magnetic) in the flight plan.

If you set UBG as the active waypoint and set OBS mode and 091, you'll miss GLARA. If you set 085(the correct radial for the VOR), then you'll hit it

If you set GLARA as the active waypoint and 271(180+91) in OBS, then you'll hit UBG.

And, of course, this is not well documented.