[MRM]

The direct cost of the 9/11 attacks were just a tiny portion of the total cost, mostly because we inflicted the additional damage to ourselves.

The solution to airport security that would prevent another 9/11 attack is simple and was partly implemented quickly. 9/11 happened because a band of hijackers were able to 1) Sneak onto airplanes with rudimentary tools that would pass a cursory security inspection; 2) Access the cockpit; and 3) Gain control of the airplane with the intent of using it as a flying bomb.

US anti-hijack doctrine had long been to surrender control of the airplane to the terrorists and wait out the siege, because until now the purpose of the hijacking had always been to use the plane and passengers as hostages, so it was easier to wait them out and nab the bad guys as they made their getaway.

So, in a fully rational world, we would respond to the incident that happened, specifically. If we did that, we would:

1) Change hijack response doctrine to not surrender control of the airplane under any circumstances.

2) Barricade cockpit doors to prevent access to the cockpit.

3) Place Air Marshalls on most flights interspersed with passengers in a way that they cannot be identified.

With those three steps there would never be another 9/11-style attack again and the ability of a terrorist to do significant harm even if a team of hijackers got inside the aircraft would be severely limited to the point that it would be a tragedy for those involved, but not a significant event in the scheme of things.

But if we did that, and only that, there wouldn't be enough disruption that people would feel a false sense of security because of all the activity they see as they try to board a plane.