The CH47 has 5 basic AI behaviors: Idle, Patrol, Orbit (combat), Egress (escape), and DropCrate.

It's difficult to unpack exactly how these behaviors work, and maybe somone with more experience with the AI can weigh in.  That said, the Patrol AI is probably responsible.  It appears that the CH47 has a "main interest point" and will start there and patrol around to nearby "interest zones".

I am speculating, but perhaps if you have a large enough map and the "interest zones" are sufficiently spaced apart, then the helicopter AI will tend to stick around one particular area.

Aye, I uderstand that but these helicopters stick to the towers like they get stuck on it and flip upsid down sometimes. Like a bug zapper, they just fly straight into in and get stuck there.