Are you using the latest Beta Patch? (not available through Steam)
You might want to check out this thread:
http://forum.1cpublishing.eu/showthread.php?t=33649
There is also a good informative thread over at ATAG. the thread has a long history going back to the original game release version, so you might want to read through it all:
http://theairtacticalassaultgroup.co...u-88-Tutorials
I hope this helps!