NTSB finds Army chopper in fatal midair crash with plane was above altitude limit

A crescendo of poor practices meeting at the wrong time...

A significant contributing factor, what are the rest?

The immediate solution to this specific situation is both simple and obvious -- which accounts for by neither the Army nor the FAA considered it before -- either shut down Reagan Airport runway 33/15 completely or stop using military helicopter route 4 completely because it is clear that neither the FAA nor the Army are capable of coordinated use of airspace that poses any risk of encroachment.

The longer term approach to the more general problem includes the legislation proposed by Sen Cruz, but that legislation is essentially the backup to the more direct approach of deconflicting military helicopter routes and airfield approach/departure routes much for strictly. Keep military helicopters away from civilian airports unless actually using that airport, and keep civilian aircraft out of areas where military helicopters need to be flying. No military helicopter should ever be within 1000 feet of any airspace authorized for civilian flight except while specifically operating under direction of an ATC. Yes, I know "that's excessively restrictive" and "we don't need that because all pilots are trained blah blah blah" -- sorry, but this fatal crash was just the product of dozens of near miss incidents that no one took action to correct the underlying problems