Putting this in the ATC forum because looking for a professional answer. Feel free to relocate to Spotters if inappropriate.
Evidently, in "turning the airport," Tower ATC didn't complete/redirect all approaches before launching planes in the new direction. Recognizing that this process is always complex, is a screw-up like this at a major airport something that (a) pretty much never happens; or (b) happens once every few years; or (b) more frequently? Thanks.
Two planes taking off from National put on collision course with plane trying to land - The Washington Post