VOR navigation trouble (Navigraph issue?)

[masconti 2]

My route from KMKC to KCPS uses V12 from ANX Vor to COU Vor via Franc intersection.

The correct magnetic heading from ANX to Franc is 88 (as reported on VFR sectional and IFR Low charts), but:

for Littlenavmap the Heading is 93 (Navigraph 2309 DB)

for Pilot2Atc tre Track is 95 (Navigraph 2309 DB)

for Navigraph Charts is 94 (update at yesterday)

Only Skyvector give me the correct heading (88).

I think may be an issue of Navigraph database

[JRBarrett 3,123]

3 hours ago, masconti said:

The correct magnetic heading from ANX to Franc is 88 (as reported on VFR sectional and IFR Low charts), but:

The number associated with a VOR radial on a published FAA chart is not (necessarily) the actual magnetic heading of the radial, nor the heading you have to fly to track it. This is a common misconception.

88 degrees is the course you set into your OBS in order track the airway (V12) with a centered CDI.

When a VOR is first put into service, the zero-degree radial is aligned with magnetic north as it existed at the time the VOR was put into service. When ANX VOR was calibrated in the year 1965, the magnetic variation at that location was 7 degrees east.

But, the earth’s magnetic North Pole is not fixed - it is continuously moving to the northwest, year by year.

The magnetic variation at the location of the ANX VOR today, in the year 2023, is 2 degrees east. The actual magnetic heading of the VOR’s zero-degree radial is now offset 5 degrees from where magnetic north was in 1965.

A VOR does not “know” or “care” where magnetic north actually is. The zero-degree radial of the VOR is an electronic reference set into the VOR transmitter by the technicians who calibrated it.

The published radial for V12 is 88 degrees. That number represents the number of electrical degrees that the radial is offset (clockwise) from the VOR’s zero degree radial, and that zero-degree radial is based on 1965 variation. It has nothing to do with the heading you have to fly (today) to track the radial.

Typically, once the variation of a VOR’s north (zero degree) radial is initially set, it is never changed again, no matter how many years pass, or how much the actual variation changes.

Most of the VORs in the western US are based on 1965 variation, and many are now offset as much as 7 or 8 degrees from magnetic north in the year 2023.

When ANX VOR was brand new in 1965, tracking V12 with a centered CDI needle wouid have indeed been done with an actual aircraft heading of 88 degrees (assuming no crosswind).

In 2023, the aircraft heading required to track the radial would be 88 + 5, or approximately 93 degrees. Navigraph and LNM show the actual magnetic heading of V12.

As long as your VOR course selector is set to 88, and you fly outbound from the VOR, (doing whatever you have to do aircraft heading-wise to keep the CDI needle centered), your track will follow the path of V12 over the ground perfectly. That would have been true in 1965, and is still true today.

 

Edited September 23, 2023 by JRBarrett

[martinboehme 523]

Fascinating - I never knew that!

Apparently, Little Navmap even has an option that lets you switch between whether to apply the current magnetic variation or the one the VOR is actually calibrated to:

Quote

Little Navmap offers several options to display course labels along the flight plan line using VOR calibrated declination or not. This can be changed in Options on page Map Display Labels.

https://www.littlenavmap.org/manuals/littlenavmap/release/latest/en/MAGVAR.html

@masconti This might be an option worth trying out. I assume on your system the option is set to use the current variation.

Edited September 23, 2023 by martinboehme
Fixed formatting

[masconti 2]

Thanks to all.

[mmcmah 442]

1 hour ago, JRBarrett said:

The number associated with a VOR radial on a published FAA chart is not (necessarily) the actual magnetic heading of the radial, nor the heading you have to fly to track it. This is a common misconception.

88 degrees is the course you set into your OBS in order track the airway (V12) with a centered CDI.

When a VOR is first put into service, the zero-degree radial is aligned with magnetic north as it existed at the time the VOR was put into service. When ANX VOR was calibrated in the year 1965, the magnetic variation at that location was 7 degrees east.

But, the earth’s magnetic North Pole is not fixed - it is continuously moving to the northwest, year by year.

The magnetic variation at the location of the ANX VOR today, in the year 2023, is 2 degrees east. The actual magnetic heading of the VOR’s zero-degree radial is now offset 5 degrees from where magnetic north was in 1965.

A VOR does not “know” or “care” where magnetic north actually is. The zero-degree radial of the VOR is an electronic reference set into the VOR transmitter by the technicians who calibrated it.

The published radial for V12 is 88 degrees. That number represents the number of electrical degrees that the radial is offset (clockwise) from the VOR’s zero degree radial, and that zero-degree radial is based on 1965 variation. It has nothing to do with the heading you have to fly (today) to track the radial.

Typically, once the variation of a VOR’s north (zero degree) radial is initially set, it is never changed again, no matter how many years pass, or how much the actual variation changes.

Most of the VORs in the western US are based on 1965 variation, and many are now offset as much as 7 or 8 degrees from magnetic north in the year 2023.

When ANX VOR was brand new in 1965, tracking V12 with a centered CDI needle wouid have indeed been done with an actual aircraft heading of 88 degrees (assuming no crosswind).

In 2023, the aircraft heading required to track the radial would be 88 + 5, or approximately 93 degrees. Navigraph and LNM show the actual magnetic heading of V12.

As long as your VOR course selector is set to 88, and you fly outbound from the VOR, (doing whatever you have to do aircraft heading-wise to keep the CDI needle centered), your track will follow the path of V12 over the ground perfectly. That would have been true in 1965, and is still true today.

 

That it one of the clearer explanations I've seen on these forums! Thank you for the edification!!

[JRBarrett 3,123]

42 minutes ago, mmcmah said:

That it one of the clearer explanations I've seen on these forums! Thank you for the edification!!

You’re welcome! The amount a VOR’s variation changes over time depends on where you are located. Here in the US northeast, the direction of the magnetic north pole’s movement is almost directly away from us in a straight line. The local variation has changed less than 1 degree in the past 20 years. In the western US, the rate of change is much faster because the direction of the pole’s movement is basically at right angles to that part of the country.

The FAA rarely changes a VOR’s north radial calibration once set, because it would result in many complications. The radial numbers would change, resulting in all publications and charts referencing the airways having to be modified. The path of a particular airway over the ground never changes, no matter how much the actual variation changes.

It’s kind of a moot point these days, since so many VORs are being either completely decommissioned, or converted to DME-only facilites.