I have been reading about 8.43.1 fixing wrong bearings, but I still seem to get wrong values for legs on iPad and in MSFS 2024 (SU 5.1 beta). The route OLM TONNO MALAY COUGA ROARK BTG should be along a magnetic course of around 151 degrees, but Charts are displaying 155 to 156 degrees for the legs. Do I miss anything? I can’t explain the 4-5 degrees difference.
Hi, this is due to a difference between actual local magnetic variation and VOR station declination.
Because the magnetic north pole moves every year, the magnetic variation in a given location changes all the time. Currently at KOLM the magnetic variation is 15°E (also visible on the airport chart).
VOR stations however, have the magnetic variation hardcoded at the physical station. This is rarely updated, since a technician has to physically go recalibrate the station, which means most VORs actually use old declinations outdated by several years. Currently OLM VOR is using 19°E.
When tracking a VOR using aircraft instruments, the VOR needles will indicate magnetic tracks based on the outdated station declination. Enroute IFR charts will likewise show tracks based on the outdated station declination, because that’s what your instruments will be showing in the cockpit.
The Navigraph Charts purple route overlay will show GPS tracks based on actual current magnetic variation, so they won’t always show the same value as the enroute IFR charts. The discrepancy varies from VOR to VOR, some VORs use station declinations that are more outdated than others.
In this specific case, the LOW IFR enroute charts show a track of ~151° from the OLM VOR, whereas the route overlay in Navigraph Charts shows ~155°. The 4 degree difference corresponds exactly to the difference between current magnetic variation and the OLM VOR station declination (15°E vs 19°E).
To put this into practical terms, when navigating using GPS, you should expect to see a magnetic track of 155° (reference the purple route line in Charts). When navigating using VOR, expect 151° (reference the applicable airways on HIGH/LOW IFR charts).
Hope this helps,
Thank you very much for the great explanation, this was very helpful!
I validated the 19°E by using the ruler and also found it in the info box after clicking the VOR(TAC); 15°E is confirmed by the dashed line nearby.