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

  1. 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.
  2. Enter the ICAO Ident of the VOR/VORDME in the VOR section.
  3. Enter the ICAO Ident of the other nav aid identified in step 1 in the Known Defined Fix/Point/Nav Aid section.
  4. The Latitude and Longitude will be automatically populated.
  5. Enter the radial identified on the chart in step 1.
  6. Click the Calculate Slaved Magnetic Variation button and the True Bearing and Mag Var fields will be populated.
  7. 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.
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