The heli update brought some crazy changes, making heli way more threatening but also way more counterable. But you can also accidentally create a no-go zone that scares heli into a flee mode fairly easily. You can see it happening if you cause it to pop flares. It's particularly easy to do if you shoot the tail rotor, so you should aim at that last.
It honestly seems like it is fairly easy to make it flee with 5 well placed shots, so you either have to take heli in 1 super strong burst, or slowly and painfully.
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