It is true that in X-Plane 922, some programmer dialed down the effective range of VORs.

That programmer was me.  (This is what happens when you let a non-pilot go poking at the nav code.)
The bug report was that a rather far away VOR could be received on the ground at KSFO; looking at the actual service volume, the notion that this could happen was crazy.  I ended up tuning the distance calculation and also the “fudge factor”.  The fudge factor is the increase in the service volume of VORs in the sim from the listed usable service volume (which is really more like a guaranteed minimum) that lives in the nav.dat file.
Here’s the real problem: VOR range has a lot to do with altitude, but X-Plane does not simulate shaped 3-d service volumes.  I think we will, but probably not for 930.  So for now we have to pick a fudge factor that is large enough to make IFR navigation work without allowing you to receive any VOR from any location.
Beta 3 is still a bit short for VOR range – beta 4 or 5 may improve things a bit.
Note that it is possible to change the service volume of navaids in the nav.dat file.  For example, KBOS and KLAX both have extended localizers; the fudge factor for a localizer doesn’t have to be 5x to allow KLAX to have a 100 nm final; the nav.dat entry for KLAX includes this special case.

About Ben Supnik

Ben is a software engineer who works on X-Plane; he spends most of his days drinking coffee and swearing at the computer -- sometimes at the same time.

One comment on “VOR Range

  1. Hey Ben. Speaking of all of this, I was talking to Robin about a problem in the nav.dat as well. Turns out that a bunch of the Low category VORs were set to the standard terminal service volume range (25 NM) instead of the standard low altitude service volume range (40 NM)!

    Of course, these are *minimums*. When I looked at the my L-1/L-2 enroute chart, I can see that some of these that were set to 20 NM, have published victor airways that force them to be longer.

    For example, Fortuna (114.0), up near Arcata, CA, seems to require reception to not less than 55 NM to the South in order to reach (JENNI) to intercept Menocino. V195, heading East, requires a similarly long 50 NM length.

    And even worse, Williams (144.4), a published route (V200) that *requires* a change-over clear out at 84 NM (which requires looking at enroute L-9 just west of Reno to find)!

    Each of these had 25 NM in the nav.dat, are categorized as low (and hence should have a 40 NM service volume), but actually have *much* bigger service volumes.

    At this point in time, I’d expect that the priority would be given to published victor airways so that IFR navigation can be practiced. As such, Robin is increasing the ranges of the ones I report, but it would seem that the airway data could be utilized to help determine necessary ranges.

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