I'm leveling up at a railway yard. I've taken out all electronics. Purple bad guys drive vehicles out of a tunnel and I take them out. Ammo box nearby. I'm having a great time - until the helicopters show up.
Is there a way to prevent the helicopters from arriving and is there an end to them or do they just keep coming no matter how many I destroy. Also, I don't seem to get many credits - tier one mode - for destroying them.
When it comes to Unidad (the purple guys), once they actually detect you and go up a Patrol level, no, you can’t prevent helicopters from responding. The higher the Unidad Patrol level, the more aggressive they are; Apache gunships will begin to respond.
For the Santa Blanca cartel (the orange guys), if they detect you, you can prevent helicopters from responding by destroying the air sirens or any generators that power the sirens in that specific area.
There's a way to stop them, though there's no surefire way to do so.
Basically you have to keep moving off road while destroying them. When you move off road, there will be no Unidad personnel can catch up with you other than the chopper ones to see your last position. In this case, when you keep destroying them and you do it quick enough, they will eventually lost you and clear the alert.
Remember, this is not surefire way. But it works for me multiple times.
For destroying helicopter not getting any Tier Point, I think that was an intended change that came several months ago to stop people from destroying helicopter back to back to grind Tier Point.
I think it was introduced in Helicopter Update where we finally have targeting dot and missile lock-on for helicopters.