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I have confirmed this to work with a Pave Low and Attack Helicopter, don't know about Chopper Gunner or Harrier.
The Killstreak you want to takedown must be inside the map (Can't be AC-130)
To do this effectively, you must have Cold Blooded equipped when you're trying to destroy it.
Wait until the helicopter/harrier is staying still, and stand right near it, and underneath it.
Lock on to it with the Javelin.
Shoot the rocket. The rocket should go forward a little bit, the straight up and hit the target from the bottom. One rocket destruction.