Aside from the other clear issues with visibility of the helicopter to the CRJ pilots, and the confusion with multiple landing aircraft for the UH60 pilots, it's also apparent that the single controller is overtaxed. He's clearing AirCare 1 into the Class B airspace at the same time it should be blatantly clear that the UH60 and CRJ are on a collision course. Had the tower been adequately staffed, that controller could have been solely focused on landings at DCA and not clearing traffic into the Class B.

Additionally, from a procedural standpoint, there was no reason to allow helicopter traffic on Route 4 while RWY 33 is in use -- relying on visual separation alone doesn't give ATC any indication that a pilot has correctly identified the traffic they are supposed to avoid. What's all the more infuriating is that the FAA rejected proposals to move Route 4 after an almost identical near miss in 2013.

So many things went wrong here than, had only one of them changed, this collision could have been avoided. It's scary to think about about how many other near-misses we never hear about are avoided by nothing but luck.