I found an exploit for the apache fight after you get the rocket launcher. It is possible to cause the helicopter to bug out so he starts aiming sideways. It doesn’t seem like it can ever turn back, and it never aims at the player again.
I have a video demonstrating it here: https://www.youtube.com/watch?v=DFcnSEmqp88&feature=plcp
I just encountered this exact exploit. In case you were wondering if it was just you. 
I didn’t have a problem with it except dying 30 times because I found it very difficult to destroy it with low health
I experienced the same exploit. After a few hits with the RPG it turned sideways, to the players left as you look out the cave. It never turned back toward me until it was destroyed.
Happens to me to. you can check this bug out like this:
Pick up some RPG-ammo outside then take out the turrets and pick up the RPG itself. Going outside again, spawns the heli. Fire the first RPG rounds then go back to where you found the RPG and pick up the remaining ammo.
Going back to the shed a second time seems to confuse the pilot
When you crouch outside exclusively then the chopper won’t lose you. Hope this helps.
Your right! I remember I went in the room to find some health. The Apache glitched when I came back out.
@Garrand:
Hi there, I have filed the bug you found in the bugtracker, coz I think I may have found a duplicate of that glitch and need “your bug” to refer to it - thx & cheers
Bugtracker-URL:
https://bitbucket.org/bmscd/black-mesa-source/issue/231/surface-tension-apache-boss-fight-chopper
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