VOR Checks

[azpilot]

A few days ago I posted this thread regarding VOR checks, and the accuracy of VOR's.

https://www.pilotsofamerica.com/com...strument-training-and-checkride.139546/page-2

I learned quite a bit in the ensuing discussion, and this morning I decided to go out and get in the plane and see if I could do all four methods of checking the two VOR's in my club plane.

Here are the results

Method 1 - VOT

I really didn't want to land at Sky Harbor. I tuned up the VOT at KPHX and got within about six miles. I could have gotten a bit closer, and was well under the bravo shelf, but I abandoned this idea. If I ever land at KPHX in the future, I'll make sure to do this check while I'm there. Six miles to the South at 3,500', neither Nav 1, nor Nav 2 could pick up the VOT signal.

Method 2 - Airborne VOR check

I flew south along V105 from PXR to TFD. There is an intersection of two roads that is very distinguishable that I used as my visual reference point. That intersection is 22 NM from TFD.

With both NAV radios tuned to TFD and the OBS set to 163, I got a centered CDI needle on NAV 1, and NAV 2 was off by by 2 degrees. Setting the OBS to 161 on NAV 2 centered the needle.

Method 3 - Dual VOR check

This was just an extension of the Airborne check. Nav 1 was centered at 163 Nav 2 was centered at 161. They were both within limits.

Method 4 - VOR checkpoint

I radioed Gateway tower and let them know I wanted a full stop. Landed on 12R. Asked ground to taxi to the VOR checkpoint, taxied over on "G" between 12R and 12C, and ran the check.

When you're at the VOR checkpoint, they have a sign installed that tells you the bearing and DME to the VOR. That was convenient. The sign at the checkpoint indicated the bearing from the station was 299 deg, and the bearing to the station was 119 degrees.

Nav 1 was centered at 300 degrees, with a from indication, and was centered at 119 with a to indication. (Note - you read that right, I tried to squint really hard to make sure I did that right. But they did seem to be off by one degree in the 'to' and 'from'. Not sure if that is user error, or something else going on.)

Nav 2 was centered at 296 degrees and 115 degrees. Off by 4 degrees in each direction.

Magnetic Declination

TFD was built at 12 E in 1985.
PXR was set at 12 E in 2000.
IWA was set at 13 E in 1980.

TFD and IWA both sit nearly right on the 10E isogonic line per the current charts. PXR is between lines as is probably at about 10.125E.

Conclusion

So both of my Nav radios passed all three checks that I was able to complete. I recorded the results of the ground check in a log that I have left in the airplane.

What I have experienced in the plane is about a 4 degree difference between the GPS reported magnetic signal, and the VOR reported magnetic signal. I know my NAV 1 radio is pretty close to dead on. I can count on it to be right between 0 and 1 degree. NAV 2 is within limits, but not as accurate. PXR and and TFD were aligned decades ago and are both now 2 degrees off from current magnetic decliation. IWA is 3 degrees off from current magnetic decliation.

 

[Walboy]

A common airborne checkpoint is V105 directly over A39.

 

[Larry in TN]

the GPS reported magnetic signal, and the VOR reported magnetic signal

It is easier to avoid confusion if you are careful with the terms used.

A GPS can give you a magnetic COURSE to fly or show your ground TRACK. You can create a COURSE on a NAVAID's RADIAL (or BEARING-to) but they won't match unless the NAVAID's declination matches the variation. The GPS' COURSE will, however, be in the correct line in space.

The VOR can display RADIALs and BEARINGs-to but they will not match exactly with the magnetic COURSE that you will fly to track them unless the VOR's declination matches the variation.

Neither the GPS nor VOR gives you a HEADING.

 

[Chicago Bearhawk]

A few days ago I posted this thread regarding VOR checks, and the accuracy of VOR's.

I learned quite a bit in the ensuing discussion, and this morning I decided to go out and get in the plane and see if I could do all four methods of checking the two VOR's in my club plane.

Here are the results

Method 1 - VOT

I really didn't want to land at Sky Harbor. I tuned up the VOT at KPHX and got within about six miles. I could have gotten a bit closer, and was well under the bravo shelf, but I abandoned this idea. If I ever land at KPHX in the future, I'll make sure to do this check while I'm there. Six miles to the South at 3,500', neither Nav 1, nor Nav 2 could pick up the VOT signal.

Really interesting. does anybody actually know the range on a VOT?
I have never done one but will look for a chance to do that whenever I see one available and in range.

 

[luvflyin]

Really interesting. does anybody actually know the range on a VOT?
I have never done one but will look for a chance to do that whenever I see one available and in range.

Read AIM 1-1-4 a., b. and c.

 

[Sluggo63]

A few days ago I posted this thread regarding VOR checks, and the accuracy of VOR's.

https://www.pilotsofamerica.com/com...strument-training-and-checkride.139546/page-2

I learned quite a bit in the ensuing discussion, and this morning I decided to go out and get in the plane and see if I could do all four methods of checking the two VOR's in my club plane.

Here are the results

Method 1 - VOT

I really didn't want to land at Sky Harbor. I tuned up the VOT at KPHX and got within about six miles. I could have gotten a bit closer, and was well under the bravo shelf, but I abandoned this idea. If I ever land at KPHX in the future, I'll make sure to do this check while I'm there. Six miles to the South at 3,500', neither Nav 1, nor Nav 2 could pick up the VOT signal.

Method 2 - Airborne VOR check

I flew south along V105 from PXR to TFD. There is an intersection of two roads that is very distinguishable that I used as my visual reference point. That intersection is 22 NM from TFD.

With both NAV radios tuned to TFD and the OBS set to 163, I got a centered CDI needle on NAV 1, and NAV 2 was off by by 2 degrees. Setting the OBS to 161 on NAV 2 centered the needle.

Method 3 - Dual VOR check

This was just an extension of the Airborne check. Nav 1 was centered at 163 Nav 2 was centered at 161. They were both within limits.

Method 4 - VOR checkpoint

I radioed Gateway tower and let them know I wanted a full stop. Landed on 12R. Asked ground to taxi to the VOR checkpoint, taxied over on "G" between 12R and 12C, and ran the check.

When you're at the VOR checkpoint, they have a sign installed that tells you the bearing and DME to the VOR. That was convenient. The sign at the checkpoint indicated the bearing from the station was 299 deg, and the bearing to the station was 119 degrees.

Nav 1 was centered at 300 degrees, with a from indication, and was centered at 119 with a to indication. (Note - you read that right, I tried to squint really hard to make sure I did that right. But they did seem to be off by one degree in the 'to' and 'from'. Not sure if that is user error, or something else going on.)

Nav 2 was centered at 296 degrees and 115 degrees. Off by 4 degrees in each direction.

Magnetic Declination

TFD was built at 12 E in 1985.
PXR was set at 12 E in 2000.
IWA was set at 13 E in 1980.

TFD and IWA both sit nearly right on the 10E isogonic line per the current charts. PXR is between lines as is probably at about 10.125E.

Conclusion

So both of my Nav radios passed all three checks that I was able to complete. I recorded the results of the ground check in a log that I have left in the airplane.

What I have experienced in the plane is about a 4 degree difference between the GPS reported magnetic signal, and the VOR reported magnetic signal. I know my NAV 1 radio is pretty close to dead on. I can count on it to be right between 0 and 1 degree. NAV 2 is within limits, but not as accurate. PXR and and TFD were aligned decades ago and are both now 2 degrees off from current magnetic decliation. IWA is 3 degrees off from current magnetic decliation.

re: the PHX VOT check…

Are you familiar with the Class B transition over PHX? You pretty much fly over the field somewhere between 4,000 & 6,000.

I’d be surprised if you couldn’t pick it up doing the transition.

 

[asicer]

Read AIM 1-1-4 a., b. and c.

That doesn't directly answer the question technically ("How far can I be and still pick up the VOT signal?"). Section (a) sort of answers it from a regulatory standpoint, though ("You gotta do what the Chart Supplement says").

 

[azpilot]

re: the PHX VOT check…

Are you familiar with the Class B transition over PHX? You pretty much fly over the field somewhere between 4,000 & 6,000.

I’d be surprised if you couldn’t pick it up doing the transition.

Yes, I've done the Bravo transition quite a few times. I was really just dealing with limited time yesterday. I knew the other three methods would work, so I abandoned the VOT attempt pretty early. I'll plan on trying the VOT in the future for sure.

 

[luvflyin]

That doesn't directly answer the question technically ("How far can I be and still pick up the VOT signal?"). Section (a) sort of answers it from a regulatory standpoint, though ("You gotta do what the Chart Supplement says").

True. Hope he read it though so will realize that there’s more to it than being able to ‘pick up’ the signal. That it can “…display out−of−tolerance readings when located at greater distances where weaker signal areas exist…”

 

[azpilot]

It is easier to avoid confusion if you are careful with the terms used.

A GPS can give you a magnetic COURSE to fly or show your ground TRACK. You can create a COURSE on a NAVAID's RADIAL (or BEARING-to) but they won't match unless the NAVAID's declination matches the variation. The GPS' COURSE will, however, be in the correct line in space.

The VOR can display RADIALs and BEARINGs-to but they will not match exactly with the magnetic COURSE that you will fly to track them unless the VOR's declination matches the variation.

Neither the GPS nor VOR gives you a HEADING.

@Larry in TN - So, let's suppose I'm working on my Instrument Rating, and my instructor tells me to track the 220 degree radial from the WIllie VOR (IWA), to intercept V105 south to Stanfield (TFD). We tune up the VOR, and start tracking the CDI. At the same time, we program the GPS to track outbound on a magnetic course of 220 from IWA (not KIWA).

In this case, the 220 radial from IWA and an actual magnetic course of 220 from IWA would be misaligned by 3 degrees, as IWA was built when the magnetic variation was 13E (but in 2022, it's on the 10E isogonic line). If the Nav 1 radio is perfect, and I have the Nav 1 OBS set to 220, I should see that there is a 3 degree difference between where I'm at, and the GPS ground track. Likewise, I would need to rotate the OBS on nav 1 by three degrees, and fly to that new radial in order to show that I'm on the GPS ground track with the CDI centered.

But if I'm flying the VOR-5 approach into KCGZ, the approach plate is designed with the understanding that TFD VOR was built when the magnetic variation was 12E. So I fly the 048 radial from TFD to KCGZ regardless of what the actual magnetic bearing from VOR to the airport is. TFD radial 048 will take me to KCGZ even if the magnetic poles flip because TFD 048 points directly at KCGZ.

Do I have that right?

 

[Larry in TN]

@Larry in TN - So, let's suppose I'm working on my Instrument Rating, and my instructor tells me to track the 220 degree radial from the WIllie VOR (IWA), to intercept V105 south to Stanfield (TFD). We tune up the VOR, and start tracking the CDI. At the same time, we program the GPS to track outbound on a magnetic course of 220 from IWA (not KIWA).

When you build a course from the VOR, the GPS will give you a course which tracks the specified radial. Since it's tracking the radial, the course and ground track may not be the same as the radial if the VOR's declination does not match the variation. The GPS knows the NAVAIDs declination and takes care of it for you so, the R-220 you entered, may end up being a course of 217 or 223, etc. No don't have to do the math yourself but you should understand why the Course/Track displayed may be a few degrees different from what you expected.

Do I have that right?

Yes.

 

[Chicago Bearhawk]

True. Hope he read it though so will realize that there’s more to it than being able to ‘pick up’ the signal. That it can “…display out−of−tolerance readings when located at greater distances where weaker signal areas exist…”

I did infact read it. And based on the Yellow highlighting and hand written notes in my FAR/AIM, it was the second time I ready it. the first most likely in 2015... But I did not remember any of these details... I have always just done the air borne dual VOR check, honestly my deviation has always been 0 between the 2 VORS so I never had to remember is it +-4 or +-6 etc...

So now I think I have a better understanding...

for airborne VOT, (which I have never done...) it clearly states "The airborne use of VOT is permitted; however its use is strictly limited to those areas/altitudes..."

 

[John Collins]

VOR navigation is based on radials, so set the VOR OBS to the desired radial and navigate based on keeping the CDI centered. GPS is a point to point system and generally uses current magnetic variation for the desired track, DTK, so in the US, there is almost always a difference between VOR and GPS. If you use a VOR as the point you are proceeding too or from when in OBS mode, your GPS will determine the course based on the selected VOR declination, but this only works in OBS mode, otherwise, GPS uses the current magnetic variation. Airports and runways also have declination that is used for approaches, but they get updated more often than VOR. So the true course while on an ILS is likely to differ from the GPS indication, but they are the same path over the ground.

 

[MauleSkinner]

If you use a VOR as the point you are proceeding too or from when in OBS mode, your GPS will determine the course based on the selected VOR declination, but this only works in OBS mode, otherwise, GPS uses the current magnetic variation.

So this is saying that a VOR OBS set to 360 should match up with GPS in OBS mode when set to the same 360 radial?

 

[John Collins]

So this is saying that a VOR OBS set to 360 should match up with GPS in OBS mode when set to the same 360 radial?

Yes, but only when a VOR is used as the fix. If one uses a named fix on an airway, the GPS will use the current magnetic variation and will not align with the radial. There is one other significant difference between how a CDI works when connected to a GPS verses a VOR receiver, the deviation indication is linear for the GPS and angular for a VOR receiver. So when the GPS is in enroute sensitivity, full scale is 2NM (WAAS) or 5 NM (non WAAS), whereas the VOR it is 10 degrees.

 

[flyingron]

VOR navigation is based on radials, so set the VOR OBS to the desired radial and navigate based on keeping the CDI centered. GPS is a point to point system and generally uses current magnetic variation for the desired track, DTK, so in the US, there is almost always a difference between VOR and GPS.

Hold the phone. You're missing concepts. GPS or VOR, the DTK changes on a straight line (great circle) as you travel along except in a couple of degenerate cases. Since it changes in either case, it's not the same as the VOR radial number (except very close to the station.