I hope you will like it!
https://www.youtube.com/watch?v=G4rCFGOAWUU&feature=youtu.be
I’m having this same problem. I hit the helicopter with ~6 rockets and then it just starts to spin there endlessly. I can’t advance or anything, it really sucks. I’m also afraid to save now because it might be glitched out forever if I do that…
EDIT: I just loaded up a previous save and the same thing happened…
I don’t know how this happened to me, but try to load like 1 Min before that helicopter. I continued playing after that glitch, didn’t see anything after that! But don’t your helicopter crash on the rocks ?
I had a similar thing happen, but the helicopter was facing away… I killed it and it spazzed out trying to hit its scripted crash site
The exact same thing happened to me too after I ran back into the cave. It faced the same direction as in your video.
I hope you could continue game after?
I’ve tried loading up multiple saves from before and making my way all the way back, but every time it just bugs out.
So, you just cant take down the helicopter?
It starts smoking and beeping all over the place, but it just spins forever and doesn’t actually crash.
Dont know how to help man, you should try to load older saves?
I had the same thing happen, as well. If you go back into the bunker (I did for cover) the chopper’s pathing seems to ignore you and its preset routines, but the cannon and rockets will still shoot at you if you come within line of fire. At least that’s been my impression.
I had to go back into the bunker because otherwise you don’t have enough rockets to take him out…
I didn’t try but, it’s not shooting you right? Why won’t you just continue?
Hey guys, this time I tried again without going into the bunker for ammo (instead leaving some outside) and it doesn’t spin around forever this time. Instead, it’s smoking and beeping and everything but it just keep shooting at me, even when I go inside the bunker and close the doors…
You need the helicopter to crash into the rocks to continune, right? Or am I missing something?
I’m not really sure about it, go inside the cave, look at the helicopter and turn right, there will be ladder, climb it up and continue.
There is no ladder in the cave. I think what it is is that the back door can be opened, but only after the helicopter has crashed. I can’t open it…
Nono, ladder is not in the cave, its outside, just look at the helicopter and go right!
Actually now it worked this time o.O
After it spinning around forever, I just shot it again 3 times with rockets (Glad I didn’t miss!) and it crashed. That’s a bit weird considering you can never miss if you want to get passed it (considering the available ammo).
I’m happy for you! 
Now have fun! And watch out for that HeadCrab in the pipe 