The real problem with this is people. Desperate people. Fanatical People. People willing to sacrifice their own lives.
The real weapon the hijackers had was their numbers, their willingness to sacrifice their own lives and their training.
A regular crew and pax had little chance against such people.
What can we do to stop this happening again ?
1. Psychological screening of all pax ?
2. Identity cards ?
3. Armed guards on all flights ?
It's terrifying, and all the security screening for knives and weapons is barely addressing the issue. The real danger is people.