FOR FS9 ONLY!
Hi, I know there are a bunch of freeware calulators for descent figuring
but for FS9 fliers that have FS Navigator, you can do a real kool thing
on the FSNav map. At about half way through your flight or 200 nm out
or so from your destination airport, set your Auto Pilot ALT at the level
for catching the ILS (i.e., 2800 ft). Then set your Vertical Speed (VS)
at -100 fpm. Zoom in on your dest airport and increase your VS until
you see an "arrow" appear on your flight path. Now decrease your
VS until the arrow is just before the outer marker of the dest airport.
That arrow means that your aircraft will attain that altitude (2800ft)
where the arrow is pointing on your flight path. Play around with VS
in order to see the arrow because it disappears if it is way out there.
But when doing this, watch for mountains in your path (FSNav
shows peak hights on map) and check out your dest airport altitude
and add (i.e. 2800) to that total and you are good to go.