But the level of sophistication which gandalftb has described in this post, leads me to believe that fuel levels wouldn't have been neglected in the planning.
Maybe something went wrong in the execution.
Well, Muslims tend to screw up a lot. The ‘workplace accident’ thing. If we assume that they did in fact plan meticulously for this, the odds of them barfing it up increases directly with the level of complexity involved. That is of course true foe the best of men with the best of skills. But when Muslims are involved, you are on the opposite end of the spectrum.
That said, It’s all just IMHO/speculation on my part. They DID pull off 911. I just think it’s more likely than not they hosed it.