Plane collides with Blackhawk helicopter Washington DC

[Zaphod58]

Normally, it could, but supposedly the helo didn't have its radar transponder turned on.  That means that the helo pilot would have been on Visual Flight Rules (VFR).  VFR requires all pilots to see and avoid other air traffic.

If you look at the traffic pattern for DCA airport, the landing approach to runway 33 requires the aircraft to stay over the Maryland side of the Potomac River until making a left turn to short final that crosses directly over the Potomac River. Helicopters transiting in that region are supposed to fly along Helicopter route 4, which is basically along the centerline of the Potomac River.  About a quarter of a mile off the approach end of runway 33, the helicopter route passes directly under the extended centerline of the runway.  That means that if the helicopter is too high and/or the landing aircraft is too low and they happen to be at the same point over the Potomac at the same time, there could be a collision. 

The helo was stationed at Fort Belvoir, which is downstream on the Potomac from DCA airport.  I don't know if it was flying to or from Fort Belvoir, but if it was flying upstream, the jet would have been approaching from over the shoulder of the helo and probably would not have been visible by the helo pilot.

Their transponder was on. There’s a lot of bad reporting going on because they didn’t have ADS-B Out broadcasting, or may not had been equipped with an ADS-B transponder. They were still broadcasting other modes.

VFR still broadcasts a transponder signal, using 1200 as their code.