Cross reference don't show actual radial?

[J van E]

Todat I discovered the cross reference option in v2 (thanks to reading the v3 manual  ;) ). However, I noticed that the information I get, isn't exact. Or not what I expected.  ;) I did a cross reference from the YXS VOR to CAH5 and it showed me I should fly on the 277 radial and the distance should be 132,4 nm. However, after doing the flight and missing the airport completely, I used the new radial option in v3 and that one showed me I had to be on the 284 or 285 radial. In the end the airport was somewhere on the 283 radial in FSX... ;)

Now I wonder where that difference between 277 and 284 comes from. Is there some way I can calculate this? I have to add that the distance to the VOR on CAH5 is 131 nm so quite a lot so even a small difference in the radial to use would get me lost. Maybe I should be using VOR for triangulation when the distances are above a certain amount?

[tim arnot]

Predominantly it's spherical geometry and the fact that VOR radials are rhumb lines not great circle arcs. So the bearing between two points will be different depending on whether you calculate from the origin point or the destination point, and the difference increases with both distance and variance from north-south.

The cross-reference is calculated from the destination point, so it will not be valid as the initial bearing if you are flying from the VOR.