According to data provided to the 9/11 Commission, the push-back (departure from gate) times and wheels-off (wheels leave runway) times for the 9/11 flights are these:
- American 11 7:40 7:59
- American 77 8:20 8:10 !!!! Wheels-off time before the push-back time!
- United 175 7:58 8:14
- United 93 8:00 8:42
The times used by the Commission, and the times in transcripts of Air Traffic Control conversations, are consistant with the wheels-off times above, except that 8:20 is used for American 77. (It's possible that the person entering the data reversed the two numbers.) However, the Bureau of Transportation Statistics gives different wheels-off times for the United flights. (The push-back times, called the actual departure times, are almost the same.) The American flights have zeros, and obviously had no actual data:
- American 11 0:00 0:00
- American 77 0:00 0:00
- United 175 7:58 8:23
- United 93 8:01 8:28
The BTS numbers are reported from data automatically transmitted (using ACARS) upon releasing the breaks and pushing back (the first numbers) and wheels leaving the runway (the second numbers). Even if the ACARS clocks were inaccurate, the time differences would have been the same if the Commission's numbers were correct.
I believe that Truther Woody Box has the most likely explanation, namely that two different aircraft took off for each of the United flights: one being the actual flight, and the other a military hijack-exercise flight actually crashed in 9/11. In any case nobody outside of Truthers has addressed the discrepancy.