Prevention Security measures Terrorism -- 5 Hijacking of aircraft -- 4 Aeronautics, Commercial -- 3 Airports -- 3 Hijacking of aircraft 2 more ... Security measures -- 2 Terrorism 2 Astronautics and state -- 1 Civil defense 1 Civil defense -- 1 Civilian use -- 1 Defenses 1 Exploration -- 1 Freight and freightage -- 1 Harbors -- 1 History 1 History -- 1 Merchant marine -- 1 National security 1 National security -- 1 Passenger traffic 1 Political aspects -- 1 Politics and government -- 1 Space race -- 1 Space security -- 1 Space warfare -- 1 Surface-to-air missiles 1 Total quality management 1 less ...