I had almost the same problem today.
I wanted to make shells explode before hitting ground for AAartillery.
see my topic
http://www.ofpec.com/yabbse/index.php?board=6;action=display;threadid=10650read the script there for details or try:
Bum="
shell" camCreate [_x,_y,_z]
where
shell is Shell125, grenade or sth
then in the same time in the same place create a rock (the same u see flying around when sth blows nearby)
it would be
Bum = "fxexploground1" CamCreate [_x,_y,_z]
When a missile hits it u got explosion ;D
et voila
make some test to set proper distance from the craft to only damage it, but not to destroy