(I) Since the terrorist attacks on 11 September 2001, anti-aircraft missile batteries have been installed to protect buildings in US cities. (II) However, less drastic solutions have also been suggested. (III) No software simulation is going to be sufficient to convince any pilot about the new avionics systems. (IV) An aerospace company, for instance, has proposed installing the electronics from its pilotless plane in passenger aircraft to allow ground control to take over a hijacked plane and land it remotely. (V) Others say automatic landing systems could steer planes to safety without human intervention.