Just to throw some grist to the mill here ...
Given that these terrorist groups are all rather well funded, what's to stop them buying a cheap B747 - ostensibly for some iffy charter operation based in, oh, let's say SHJ - and then fly it with theior own crews into whatever buildings they want without having to go through the whole hijack process in the first place?
Lowers the potential casualty numbers slightly - but you'd have a far higher chance of success!
Guv,
What you've proposed is exactly what went through my mind as I watched what I thought to be a 737 fly into the second WTC tower on the 11th! I really hadn't considered that they were hijacked airliners! With all the oil money floating around the mideast, I figured that some deranged millionaire financed a few 737s, and had them flown into the WTC.......I was OBVIOUSLY wrong!
BTW, are you any relation to Brian May?