If it is a co-ordinated attack, it would not take much more than a six pack of soda cans filled with ammonia and another six pack of bleach to create a noxious gas on a plane. Considering the reaction, checking all liquids, my guess is they were trying something along those lines. While I do not think that would be "an unimaginable scale" compared to 9/11, it could easily be done.
I agree.
"While I do not think that would be "an unimaginable scale" compared to 9/11, it could easily be done."
Unless there were more than 6 planes involved, (I heard 21 on the news as a possiblity), and if all of those were used as weapons....press conference authorities used stronger language this time than I've recently heard.