[bsder]

The problem that prevented any solutions was the reinforced door. The security theatre was worse than theatre--it backfired.

At this point, the flight crews are a bigger threat to passengers than terrorists. Since passengers won't sit still for a hijacking anymore, terrorists effectively aren't a threat.

You don't need a heavily reinforced door. You only need one that prevents entry for a few seconds while the passengers figure out that they need to subdue the attacker.

[SoftTalker]

Yes that's true, but in this case only because Lubitz chose to use the autopilot to make a controlled descent into the mountains. He could have put the aircraft into an unrecoverable nosedive while the captain was in the lavatory, and saving it would have been impossible even if the captain had been able to get back into the cockpit.

[bsder]

That is also true, but most people committing suicide like this want an audience. Otherwise, they'd simply do it alone. Many times they kind of even want someone to stop them. That gives you time.

We could have changed nothing after 9/11 and it couldn't have been repeated. The fourth plane is an example of that.