Harlan Ullman on Fox points out that a plane loaded with fuel and taking off from Heathrow would make a much bigger impact diving into the Parliment building than after most of the fuel had been burned off flying across the Atlantic.
Excellent point. Especially since, first, we know al Queda makes a habit of trying to go after targets they've gone after and missed (hence all the concern about LAX) and second, a little known fact: there was a fifth hijack team on September 11th -- but it was in London. As I have mentioned before, back when I was at blogspot, (scroll down to "Is This Why Tony Blair is So Loyal?") this is the conclusion of one of the world's foremost al Queda experts, Rohan Gunaratna, after debriefing the terrorist he believes to have been the intended hijacker-pilot, when the man was later in Indian custody. Money quote:
"[Al Queda] planned a simultaneous attempt to destroy the House of Parliment by crashing into it a British Airways aircraft hijacked from London's Heathrow airport. Muhammad Afroz, an Indian suicide pilot trained in Melbourne, Australia, Britain and the US was subsequently arrested in Mumbai, India.".