VOR's and VORDME's use slaved magnetic variation. This value indicates the magnetic variation at a point in time - either the installation date of the VOR/VORDME or the date of the last alignment to magnetic North. Over time the magnetic variation in the area of the VOR/VORDME changes so that the nav aids North radial (0 degrees) no longer aligns to magnetic North.
When calculating using VOR/VORDME's, the slaved magnetic variation must be used.
There are two ways to update a VOR/VORDME's slaved magnetic variation:
Create a Custom Nav Aid
If you have an up to date slaved mag var value for a VOR/VORDME you can simply override the existing data by creating a Custom Nav Aid. Enter the ICAO Ident of the VOR/VORDME and the fields will be populated. Update the Slaved Mag Var field and click the Save button.
Calculate the Slaved Mag Var
- Locate a chart that contains the VOR/VORDME to be updated and also contains a radial bearing from the VOR/VORDME to another nav aid.
- Enter the ICAO Ident of the VOR/VORDME in the VOR section.
- Enter the ICAO Ident of the other nav aid identified in step 1 in the Known Defined Fix/Point/Nav Aid section.
- The Latitude and Longitude will be automatically populated.
- Enter the radial identified on the chart in step 1.
- Click the Calculate Slaved Magnetic Variation button and the True Bearing and Mag Var fields will be populated.
- Click the Save button. Note this will create a Custom Nav Aid using the existing VOR/VORDME data but with an updated slaved mag var.