Just an informational post -
A while back I was searching for a way to trigger an event on the death of a monster_apache.
The usual triggerTarget/triggerCondition key/values do nothing with this monster unfortunately.
However there is one workaround depending on the setup of your map:
monster_apache will activate a brush based trigger with the flag "monsters" set WHILE it is in its death spiral flying to the ground to blow up.
So, if you give an apache a flight path above a trigger, such that the apache will ONLY fly through the trigger when it falls from the sky and dies, you can detect the death spiral of the apache and then trigger events.
Of course, you cant put the trigger somewhere that other monsters might activate it, but with a bit of clever placement you can make it work in a lot of situations.
Enjoy