article_snippet.sent: I think that there's absolutely a gap, and it's a very dangerous gap, with regard to our airspace,' Cummings said. '
article_snippet.sent: That could have been a major catastrophe.'
article_snippet.sent: The landing on the Capitol grounds 'just illustrates how hard it is to have an impermeable barrier.
article_snippet.sent: It's very hard to hermetically seal airspace,' said John Hansman, a Massachusetts Institute of Technology aeronautics professor.