"mass murder on an unimagineable scale"
Which means there were more than 6 planes involved...
And which probably also means that the plot was more than blowing up planes on transatlantic flights.
Are liquids being banned for explosives? Or, could the matrial be used to disable a plane load of people. Thus, there would be more "missiles" capable of killing an extraordinary number of civilians.
Our casualty count for 9/11 was 3,000...this attack needed to be cataclysmic in order for the authorities to make the above chilling statement.
Domestic levels raised, Egyptian students missing...more to this than we know yet.
It seems that they planned to blow them up over major American cities during approach.
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.