Firstly I should like to express my deepest condolences and sympathies to all who have suffered in this despicable act of terror.
I echo the sentiments of Apollo entirely. Of course it was Mass murder by incredible stupidity, no doubt about that, especially after seeing that the "pilots" were some of us. However, the flight deck, the cabin and for all I care the cargo bays and wheel wells MUST be held sterile. This means no weapons and/or explosives whatsoever. Accordingly, the security and safety agencies, whatever their abbreviation may be, but as well as the airlines have to ensure the professional safety of PAX, crew and equipment; not the crew. What strikes me especially worrying is the fact that four airplanes from to companies could get high jacked in the first place with absolutely on one even suspecting any foul play at work. Should by any chance a Sky Marshall have been on these flights, I am not at all sure whether it would have had any difference to the outcome of the tragedy.
There should be no weapons on any flight; there should be a closer screening of anyone involved with the aircraft; we should be able to rely on our Intel. Services, and law enforcement and our employers to guarantee a "sterile" flight.