The logic is based on the fact that DCA
is so close to the White House, US Capitol, and the Pentagon. When planes approach DCA
from the north, all of these landmarks are clearly visible, and a hijacked plane could easily appear to be approaching normally before making a sudden turn into one of these buildings. The 30-minute rule is a safeguard -- if anyone stands up, divert immediately before any hijack can take place. Personally, I don't know how effective this is, but I understand the argument. This was the price we paid to have DCA
reopened. Remember, it was closed long after all other airports reopened; there was serious talk at the FAA and Secret Service about closing it permanently (although I don't think that would have ever happened, due to DCA
's political clout).