Originally Posted by
Luc Lion
200 ft is not the separation between the 2 aircrafts, it's the maximum altitude allowed in the helicopter corridor. As the airplane on approach is supposed to be at about 250 ft when crossing this corridor, there is no way a 200 ft separation could ever have been achieved.
500' vertical, parallel separation is what a TCAS RA/Resolution provides. At the heights of the involved, RAs are suppressed. Hence why the Republic had to go around the day prior, but the 737, earlier and lower did not.
500' is also the VFR and IFR vertical offset standard. If unable to achieve, should not be allowed. 200' leg must be to be 500' below south flow DCA departures, so North flow arrivals need a better gate.