TD, as you rightly state the situation of a bag travelling without its owner was not the case on 911.
Many other situations were similarly not encountered on 911, such as private flights by aircraft not N-registered. So why are they banned? For several days afterwards, flights into the USA were banned. Why?
Many other security provisions have been put in place in the USA since 911, when they guard against methods of terrorism that were not employed on 911.
Yet, this precaution is not popular with the airlines. Simply because it will inconvenience them, and cost them money. Yet, as things stand, downing an aircraft this way would be the simplest thing in the world to carry out.
Apart from terrorism, implementing such a precaution would have the very welcome side-effect of resulting in far fewer lost bags on US flights.
[ 09 November 2001: Message edited by: HugMonster ]