Garmin Pilot App - Ruler Feature ...what I am missing

[texasclouds]

See attached picture. I used the ruler feature to draw a line over the 021 radial. The ruler says my line is 19.7 NM long and is pointing towards a magnetic heading of 026. The magnetic variation is -7E, but I had expected the two to match since the vortac radials are magnetic not true course. I am assuming the 026 M means magnetic. What I am missing here?

 

[Van Johnston]

I’ve seen this type of discrepancy before, and I don’t like it...

Put FST to MAF in your flight plan and check mag course and true course. Mine says TC=032 and MC=026. (GP on iPad).

Now, in map mode, go put your finger on FST to pop up its details, and note it says the variation is 11 deg. So 32 - 11 = 21.

Also note the closest isogonic line to FST IS 7 deg E.

As to why the variation for FST is so different from the isogonic line, I don’t know. GP’s calculation is closer, but still a degree off. Maybe others have better insight to the synchronization, or lack thereof, of FAA database and chart updates, and real world.

 

[dmspilot]

The VOR's magnetic variation of 11°E is from 54 years ago (1965) which explains 4 degrees of the discrepancy, with the remaining degree probably rounding error.

 

[texasclouds]

Shouldn’t the current sectional chart have updated VOR info? Like when they rename runways due to changing magnetic N? Will I find similar differences on a paper sectional chary?

 

[dmspilot]

Shouldn’t the current sectional chart have updated VOR info? Like when they rename runways due to changing magnetic N? Will I find similar differences on a paper sectional chary?

It's not an issue with the chart, it's an issue with the physical alignment of the signals transmitted by the VOR. The radials were aligned with magnetic north in 1965 but no longer. It's like a runway that hasn't been renamed, and now the numbers are wrong.

The number printed on the chart, 021° in this case, is the radial of the VOR, not the magnetic course along the airway, which would have been 021° in 1965, but as you discovered is now 026°. The radial 021° is like the runway number that hasn't changed with the times.

 

[texasclouds]

Thanks