"If a dry run is occurring, the attack will shortly follow." That's according to Wolf Koch, a Boeing 767 pilot for Delta Airlines and an official at the Air Line Pilots Association International, who was discussing common terrorist tactics in the run-up to devastating attacks like those on 9/11. That is an extremely worrying thought given a memo leaked this week from the U.S. Airline Pilots Association, which warns of "several cases recently…of what appear to be probes, or dry runs" of such attacks.