Gentlemen,
Making an aircraft "safe" IMHO is a very difficult task nearing the impossible when considering the numbers of people that have access to a long haul aircraft all over the world and the number of everyday objects that one can use as a life threatening device.
Security should start at the booking stage and not just at the end of the aerobridge as it was in the States until recently. In addition to this maybe we should also be looking at changing the way security is run at the airports when people do eventually get there. Just asking a few questions is not enough in my mind. We have all heard reports of recently released felons working airport security around the world and maybe this is one way to start. Unfortunately the saying "pay peanut, get monkeys" jumps to mind.
The comments of Boing are on the spot I feel and while they should be heeded, awareness in the cabin is surely a good way to help when it comes to a potential hijack situation rather than padlocking every door, hatch and access panel in sight.
These were 4 airplanes that were hijacked on the same day as many, many more took off on perfectly routine flights. The percentage loss was minimal and I have always taken it as a risk of the job. Locking doors diverts the focus of the attack somewhere else and puts others at further risk and possibly ourselves at greater peril once access is gained to the flight deck.
In short, vigilence has got to be a much greater step than the brightly coloured steel bars talked about by another contributor.