XML: VOR Radial Sign Rules
From FSDeveloper Wiki
(A:NAV1 RADIAL, degrees) (FS9) and (A:NAV RADIAL:1, degrees) (FSX) can return negative values.
When this happens, add that value to 360 degrees to get the actual Radial:
(A:NAV2 RADIAL, degrees) 0 < if{ 360 (A:NAV2 RADIAL, degrees) + (>L:VOR2 Radial, degrees) } els{ (A:NAV2 RADIAL, degrees) (>L:VOR2 Radial, degrees) }
In this example, (L:VOR2 Radial, degrees) represents the correct radial.
Applies in FS9 and FSX, NAV1 and NAV2.