I agree securing the cockpit door (plus the new cabin cameras so the flight crew can see in the cabin) along with passenger awareness means its unlikely there will ever be another in flight incident like 911. No crew would ever open the door and no future passengers would sit back and do nothing.

Targeting a shopping mall or high speed train would be a lot easier and just as effective. Its an oxymoron at Heathrow where shoes are removed for x-ray except when its busy (generally every two minutes or so) and the staff allow it to be bypassed. In fact in terminal three the far left immigration lane lane usually walks by most of the time as any frequent traveller (or terrorist) would know.

If you take the time to read about how to make a liquid explosive (widely available on the web) its completely implausible that could ever be a serious threat.

The best weapon if you are so minded is already allowed on board being duty free liquor. The obvious risk is having several hundred liters of flammable substance rolling around overhead lockers unsecured in glass bottles and the chance of bottles falling on passengers heads (I have seen this).

However they also make great clubs as demonstrated by the hijacking some years ago of an Air NZ B747 in Fiji whilst on the ground where the hijacker was clubbed and knocked out by the flight engineer with a bottle of duty free.

Breaking it on a galley/toilet edge would make a handy knife and it would be easy to make into a molotov cocktail. I guess airlines and airports make too much money from duty free sales to do anything about it so thats why they like to pick on grandmothers with nail clippers! Heaven forbid a rampaging 80 year old grannie on the loose with nail clippers.

The sad part is the guy is sitting in a cave somewhere in Afghanistan is no doubt laughing at the chaos we have allowed to be inflicted on ourselves and knowing we have inflicted on ourselves much more chaos and disruption than he could ever have.