toadlife's HALO script in the Ed Depot might be the thing you're looking for.
The best way to make a chopper fly at a certain height is to use the command flyinheight. Or, if you want to setpos it to a certain height at a certain place put a gamelogic on the ground at that place and use the command line
chopper1 setpos [getpos gamelogic1 select 0, getpos gamelogic1 select 1, (getpos gamelogic1 select 2) + h]
where h is the height you want in metres. Syntax not guaranteed.