Reply #71: Your guarantee is not satisfying

[Woody Box]

because it takes for granted that one or both UA 175 were ordinary civilian flights.

We know, however, that the military performed several exercises on that day. In the past, some of these exercises have been designed as realistic hijack scenarios, with Pentagon employees posing as passengers etc. Suspiciously, many of the 9/11 passengers were employees of Raytheon, a company providing the Pentagon with radar systems, electronic devices, etc. Furthermore, the crews of at least some of the flights were replaced last-minute for unknown reasons, fueling the suspicion that they were part of a secret military operation:

http://shoestring911.blogspot.com/2008/03/last-minute-pilots-passengers-and.html

I accept that neither ATC personnel nor computer software accept two planes with identical call signs or transponder codes. But it is perfectly possible that the UA175 that sent the 8:23 takeoff message to its airline used another call sign and/or transponder code when communicating with ATC - exactly because it was part of a secret military exercise, like I said. For the same reasons, it is perfectly possible that controllers were informed that a secret military exercise was going on and therefore accepted the identity change of UA175.