Creative Speculation

...how curious! Why would one need to swap planes if they're already in the software? The sky's (pardon me here) the limit. One has prevented their hijacking signal from being sent and in fact, while we know that pilots were alive outside of the cockpit, there is really very, very little said over the radios from the planes and except for flt 93 I believe, nothing hijacking-related at all from the others. It would seem their comms are taken down. At the same time there are three other planes that day sending out false hijacking signals, one plane even three times but none of the four hijacked sent any signal. Sowing confusion. Someone was the ghost in several machines and there's no telling how much control over the planes they might have had.