An American Black Hawk helicopter collided into the flightpath of American Airlines AA5342. So far 19 bodies have been recovered from Potomac River in Washington DC.

It looks like the helicopter made an intentional effort to crash into the plane. The sky is clear and the landing lights on the plane are blazing brightly so they must have seen it. The air traffic control tower also doesn't tell the helicopter to take evasive action to avoid a deadly crash. 

What is going on and how was this allowed to happen?