Both VOR’s Off by 36 Degrees

MBDiagMan

MBDiagMan

Final Approach
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This indicates to me that the problem is not with the instruments themselves but either the antenna, antenna cable or splitter, since they are all common to both radios.

My money is on the splitter. Any comments or experience to share?
 
I do use GPS, but there is this thing called a Radio Log that has to have an entry within the last 30 days or so. One of the VOR’s is the one from the 430 W. I can’t fly IFR legally without properly working VOR’s.
 
I thought that with the "W" model (WAAS) you were allowed to fly IFR without terrestrial navaids.
 
MBDiagMan said:
I do use GPS, but there is this thing called a Radio Log that has to have an entry within the last 30 days or so. One of the VOR’s is the one from the 430 W. I can’t fly IFR legally without properly working VOR’s.
Click to expand...
The gps 430w can be primary nav. No Nav receiver required.
 
MBDiagMan said:
I do use GPS, but there is this thing called a Radio Log that has to have an entry within the last 30 days or so. One of the VOR’s is the one from the 430 W. I can’t fly IFR legally without properly working VOR’s.
Click to expand...
That's the funny part. You CAN fly LEGALLY (but stupidly) because the regs require that there be no more than 4°difference between the two units (FAR 91.171 (c). Now you know and I know that you will wind up in Texas if you aim for Missouri, but LEGAL, friend, LEGAL.

And yes, you can fly legally without the VORs with an IFR GPS.

I do have a stupid question. Why whenever there is electronic malfunction is the stock answer either (bad ground)(dirty connection) (something spelled "antenna"). Somebody gotta 'splain to me how a bad antenna, coax, or coupler will cause the VOR signal to be off by 30+ degrees without so much as a by-your-leave to ask how the ident signal is coming through.

Jim
 
Thanks for the great posts!

I have been under the impression that if there are instruments, they must be operational. One of the VORs is the one that is part of the 430W. If the 430W without an accurate VOR is legal for approaches I still want to fix the VOR’s but the immediate need goes away. Is this plane legal for IFR? It is currently IFR certified.

I remember you Jim. You showed some rewiring you did on a 172 as I recall. Although my career migrated toward software long before I retired, I had radar and other electronic experience along the way and I too find it difficult to understand how an antenna or a piece of coax could cause this problem. The splitter is a different animal since it assumedly has passive components incorporated. Do you agree that the problem is likely the splitter?
 
Clark1961 said:
...The navs might have to be labeled inop and a log book entry made to be legal.
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I'm pretty sure that is required, and they would have to be deactivated as well. I'm not sure there would be any way to do the latter when they're integrated with the GPS, as is the case with the 430W.
 
Palmpilot said:
I'm pretty sure that is required, and they would have to be deactivated as well. I'm not sure there would be any way to do the latter when they're integrated with the GPS, as is the case with the 430W.
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‘Deactivated’ might leave room to disconnect the nav antenna. Usually the inop item is de-energized but maybe disconnecting the antenna would suffice in this circumstance.
 
“you can fly legally without the VORs with an IFR GPS”

It’s my understanding that we can fly legally (even IFR) without VORs, but a VOR approach must be done with a VOR receiver and can’t legally be done with just a GPS. That’s what the G1000 in the plane that I rent tells me whenever I load a VOR approach into a flight plan. (I know the G1000 isn’t an aviation lawyer or FAA official, but it wouldn’t lie to me about a thing like that, would it?)
 
Would you want to fly in the soup with VORs marked INOP and hope the GPS doesn't die?
 
Lon33 said:
“you can fly legally without the VORs with an IFR GPS”

It’s my understanding that we can fly legally (even IFR) without VORs, but a VOR approach must be done with a VOR receiver and can’t legally be done with just a GPS. That’s what the G1000 in the plane that I rent tells me whenever I load a VOR approach into a flight plan. (I know the G1000 isn’t an aviation lawyer or FAA official, but it wouldn’t lie to me about a thing like that, would it?)
Click to expand...

That is accurate. You must have the raw VOR signal displayed "somewhere" in the cockpit. You can have the GPS-derived course shown on your primary NAV display if you like, but the VOR signal must be somewhere.
 
MBDiagMan said:
I remember you Jim. You showed some rewiring you did on a 172 as I recall. Although my career migrated toward software long before I retired, I had radar and other electronic experience along the way and I too find it difficult to understand how an antenna or a piece of coax could cause this problem. The splitter is a different animal since it assumedly has passive components incorporated. Do you agree that the problem is likely the splitter?
Click to expand...

I absolutely DISagree. The passive components in a splitter are either a bifilar wound transformer OR a couple of quarter wave sections for a Wilkinson splitter. And a 100 ohm resistor to balance the legs. THe transformer is either open or good. The coax is either open or good. Nothing in the splitter is going to make the VORs off by any measurable amount, certainly either completely dead or in the hundredths of a degree if some absolutely freakish failure has occurred that unbalances the legs. Even then, a mouse hair across the balance resistor won't do any more than reduce the signal, not create a phase shift in the subaudible range of the RF signal.

JIm
 
MBDiagMan said:
This indicates to me that the problem is not with the instruments themselves but either the antenna, antenna cable or splitter, since they are all common to both radios.

My money is on the splitter. Any comments or experience to share?
Click to expand...
Something interfering? Any new electronics added lately?

Sent from my XT1585 using Tapatalk
 
It sounds like they would pass a dual-VOR check, so what's the problem? ;)
 
Another helpful testing tool is the graphical CDI built into your 430W. Compare it to your analog CDI's and see which one is in error.
 
weirdjim said:
I absolutely DISagree. The passive components in a splitter are either a bifilar wound transformer OR a couple of quarter wave sections for a Wilkinson splitter. And a 100 ohm resistor to balance the legs. THe transformer is either open or good. The coax is either open or good. Nothing in the splitter is going to make the VORs off by any measurable amount, certainly either completely dead or in the hundredths of a degree if some absolutely freakish failure has occurred that unbalances the legs. Even then, a mouse hair across the balance resistor won't do any more than reduce the signal, not create a phase shift in the subaudible range of the RF signal.

JIm
Click to expand...

Thanks Jim! Great explanation and sharing of experience.

Since being away from the thread I was sitting at my IA’s desk and an avionics book was setting on the table. I picked it up while he was working on my logs. From the book, it sounds like this is likely an antenna bonding problem. I will be back at the hangar tomorrow and pursue it further. The biggest problem for me to overcome is not having a test set or a VORthat can be tuned from the ground. The airport where I used to hangar has a VOR five miles away that you can receive on the run up pad. I have friends including an IA there with plenty of tools, so I might plan on spending a day there.
 
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