In "Route Kanal" there're a couple of sequences in which the apache helicopter seems to move around to get the best angle for targetting you.
This example map demonstrates one way to accomplish that aggressive behavior by positioning path_tracks where the apache can fire at various positions where the player can "hide."
At each of those "hiding" positions is a triggle_multiple that changes the helicopters current path_track to the position where it can fire on you.
The map consists of a simple hallway with openings on either side. As you crouch behind the wall on one side of the hallway, the helicopter moves to the opposite side. By placing several triggers along the hallway, the helicopter moves along with you, forcing you to zigzag from side to side as you progress down the hall.
Some testing indicates that the triggers work better if they don't touch or overlap.