Prevention Security measures Terrorism -- 5 Aeronautics, Commercial -- 2 Airports -- 2 Hijacking of aircraft -- 2 Security measures -- 2 more ... Civil defense 1 Civil defense -- 1 Defenses 1 Freight and freightage -- 1 Harbors -- 1 Merchant marine -- 1 National security 1 National security -- 1 Passenger traffic 1 Politics and government -- 1 Surface-to-air missiles 1 Total quality management 1 Transportation -- 1 War on Terrorism, 2001-2009 1 less ...