VOR off course

cgrab

cgrab

Pattern Altitude
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May 2, 2014
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Huntsville AL
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cgrab
I was out flying the other day and decided to use my one VOR to check the three GPS's in the plane. I was flying due south looking at the VOR and when I centered the needle it shower 150. I turned out and made another run in on course 100 and it centered up on 110. My first thought was that I don't know if it is the KI209 or the KX155. How do I figure that out and how do I fix which ever is out? We don't have a VORTAC at our airport so I would need a source to check against.
 
What are you comparing?

Few VORs, if any, will have their 360 radio aligned exactly with magnetic north. The difference between the two is the VORs declination. You need to setup your GPS to fly a radial, not just your direct track (DTK) in order to compare to the VOR radial.
 
FAR 91.171 is pretty clear on how to perform VOR checks.

Here is the way to do an air check:

(i) Select a VOR radial that lies along the centerline of an established VOR airway;

(ii) Select a prominent ground point along the selected radial preferably more than 20 nautical miles from the VOR ground facility and maneuver the aircraft directly over the point at a reasonably low altitude; and

(iii) Note the VOR bearing indicated by the receiver when over the ground point (the maximum permissible variation between the published radial and the indicated bearing is 6 degrees).
 
cgrab said:
I was out flying the other day and decided to use my one VOR to check the three GPS's in the plane. I was flying due south looking at the VOR and when I centered the needle it shower 150. I turned out and made another run in on course 100 and it centered up on 110. My first thought was that I don't know if it is the KI209 or the KX155. How do I figure that out and how do I fix which ever is out? We don't have a VORTAC at our airport so I would need a source to check against.
Click to expand...

Using GPS to check VOR I can see. Using VOR to check GPS is like using a sundial to check a stop watch
 
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Using GPS to check VOR I can see. Using VOR to check GPS is like using a sundial to check a stop watch
Click to expand...
Next time I'll figure out how to use the smiley to denote a joke.
 
Does Huntsville Intl. still have a VOT signal? On surface, 111.00, set OBS 180 with a To flag.
 
I used the VOT at KHSV and the TO lined up 29 degrees off and the FM lined up 26 degrees off. How do I know if the receiver (KX155) is putting out the wrong signal or if the indicator (KI209) is just misinterpreting it?
 
cgrab said:
I used the VOT at KHSV and the TO lined up 29 degrees off and the FM lined up 26 degrees off.
Click to expand...

Does your ISP charge you by the character? If not, would you please interpret the above so we know what you are talking about?

Thanks,

Jim
 
cgrab said:
I used the VOT at KHSV and the TO lined up 29 degrees off and the FM lined up 26 degrees off. How do I know if the receiver (KX155) is putting out the wrong signal or if the indicator (KI209) is just misinterpreting it?
Click to expand...
There is no "wrong signal".

The VOR transmits two signals or "tones". One is fixed, the other variable (based on direction). The receiver decodes the two "tones" and sends them to the indicator. The indicator compares the phase of the two signals and the difference between them is displayed by the CDI. When the phases match the needle is centered. The OBS knob adjusts a phase-shifter to change the desired needle-centered point.
 
OK, with the plane out of the hangar and pointing east. I tuned the KX155 Nav to 111.0 which is the VOT at KHSV. I turned the OBS until the needle was vertical with both the TO and FM flag. The dial indicated 151 with the TO flag and 334 with the FM flag. The VOT transmits on the 360 radial so I am out 26 or 29 degrees.

How do I determine if the receiver is decoding improperly or the indicator is not comparing them properly?
 
cgrab said:
OK, with the plane out of the hangar and pointing east. I tuned the KX155 Nav to 111.0 which is the VOT at KHSV. I turned the OBS until the needle was vertical with both the TO and FM flag. The dial indicated 151 with the TO flag and 334 with the FM flag. The VOT transmits on the 360 radial so I am out 26 or 29 degrees.

How do I determine if the receiver is decoding improperly or the indicator is not comparing them properly?
Click to expand...

You don’t. Take it to an avionics shop and get it diagnosed.
 
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But seriously. Would Just have avionics look at it quick.
 
Actually, declination is the difference between the VOR's 360 radial and TRUE north.

Note, that except in degenerate cases, the actual bearing to the station (what the GPS is displaying) is not the same as the radial even when the VOR is perfectly aligned with magnetic north.
 
cgrab said:
OK, with the plane out of the hangar and pointing east. I tuned the KX155 Nav to 111.0 which is the VOT at KHSV. I turned the OBS until the needle was vertical with both the TO and FM flag. The dial indicated 151 with the TO flag and 334 with the FM flag. The VOT transmits on the 360 radial so I am out 26 or 29 degrees.

How do I determine if the receiver is decoding improperly or the indicator is not comparing them properly?
Click to expand...

The direction the airplane is pointing makes no difference.
 
cgrab said:
How do I determine if the receiver is decoding improperly or the indicator is not comparing them properly?
Click to expand...
Comparing what to what? On the 155 all the radio puts out is a l/r signal to the indicator. On other radios like the 165, the indicator processes the phase errors between the two parts of the VOR signal.
 
flyingron said:
Actually, declination is the difference between the VOR's 360 radial and TRUE north.
Click to expand...
Right, which can be compared to the current local magnetic variation to see how close the VOR radials are to magnetic courses.
 
There is an adjustment screw that is located behind the upper panel mounting screws. The LH side is for the VOR and the RH is for the Localizer (I think).

Your avionics shop will have the special tool to make the adjustment. They will turn it like how you adjust your altimeter.
 
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