The NTSB has issued their preliminary accident report and an accident investigation report with two
urgent safety recommendations. These are available via
https://www.ntsb.gov/investigations/Pages/DCA25MA108.aspx .
In any aircraft accident investigation, there's a preliminary report after about a month. It contains the "obvious" facts, i.e. it describes what happened. How and why it happened is set down in the final report, which can take a year or more to produce.
Here's what I found important:
1) The Blackhawk's voice recorder indicates that the crew did not receive key information from ATC that would have helped them understand the situation.
2) At the time of the collision, the jet's left wing was low, and its aft end was down (i.e. the pilot was likely trying to evade left and up); the helicopter severed that wing, and its tail rotor hit the back end of the aircraft. The right wing then rolled the aircraft through 1¼ turn.
3) The DCA airport has a history of dangerous situations. NTSB chair Jennifer Homendy read out the following information at the latest briefing. She indicated that the FAA was examing other airports for these types of danger signs.
4) The accident investigation report is very clear that operating runway 33/15 and heli route 4 simultaneously is a bad idea, and should stop.
The NTSB is planning visibility studies and witness interviews to get a clearer picture of what the situation looked like from each cockpit and from the tower. They're also going to look at tower staffing, and at how the army is using the ADS-B transponders on its Blackhawk fleet. For now, most helicopter traffic on route 4 is suspended via NOTAM, but that's not a long-term solution.