It seems to me that a lot of the debate around aviation security is that we (generally) are conflating two separate questions:

1. What measures are appropriate to ensure the safety of the passengers on the plane.

2. What measures are necessary to ensure that the plane is not turned into a weapon against others (i.e. crashed into a building).

So long as we have secured cockpit doors, it seems that #2 is largely resolved. "Another 9/11," with a group of men armed with knives/box cutters couldn't turn a plane into a giant cruise missle. They could, however, do a lot of harm to the passengers on that plane.

It seems to me that there is a genuine national security interest in mandating safety precautions to block #2, since that sort of attack affects people who have nothing to do with the flights themselves. In terms of #1, however, airlines should be allowed to choose whatever level of security they want to pursue (i.e. screen for bombs or don't), and let the passengers decide.

So, this would lead to a Federal mandate banning carrying on items that could credibly allow passengers to breach the secured cockpit door (i.e. no SWAT solid-slug shotguns, no sledgehammers, no crowbars), but knives (which could in theory wreak havoc in the cabin, but can't seize the plane) and liquids (I know there's debate over this, but for the sake of argument, assume they could be used to make a bomb) would be allowed, as they only present a risk to the passengers on the plane.

Well thought out and articulate.

I also disagree with your contention that the door defeats knives. It only does so when its closed, and in most flights I've been on its opened at least three, but most likely four times, a flight.

That's when I'd make my move.

A tool is only as good as its use.

If I had a tool that I'd never needed, and even then it could only be found in my toolbox 5% of the time I looked for it, I'd question the usefulness of the tool, no matter that it be the best tool ever made.

A more useful place to apply resources these days, though probably not the armed, buff ones, would be here:

http://www.flyertalk.com/forum/showthread.php?t=673058

Armed, buff tools could find lots of action in OMNI. (but not from me)

Seriously, wide scale tampering of human food products is a real issue. I'm not normally a paranoid person, but if I were a terrorist, I'd make a probe into the system that looked exactly like this one.

I don't think that's likely to happen. Given 9/11 I'd imagine the next person to try to threaten people with a knife on a plane is likely to get stomped. Sure, 1 or 2 people may get hurt or killed, but I can't see that would stop the rest of the passengers and crew if they think that there's a chance they're going to be used as a missile.

Not really. Any security system is only as good as the humans involved, and it is difficult to say whether an FA with a knife to her throat would try to get the door open on demand or not.

It's more the changed likely response of passengers to an attempted hijack that would prevent this than whether the door was of the traditional type, more secure or wide open.

Relatively recently in the UK there was an issue with contaminated petrol that affected petrol sold in some supermarkets most notably Tesco. This caused engine damage to a lot of customers cars (at least thousands). I always thought it could be a malicious action, maybe by someone who wanted to cause damage to Tesco or the petrol supplier or some misguided environmentalist who wanted to punish car drivers.

But whatever people's motives it does seem a lot of damage can be caused by contamination.

I brought this concept up a long time ago and I got baked on here for it. Everyone on the plane has a right to be secure against attacks. This means that even though the whole plane was not used as a weapon when the passenger in 3a pulled a knife and started slashing other people, those other people could have been protected. You cant let some things go on a premise that the passenger beware. One thing that I have learned is that people DONT read signs, DONT listen to announcements, DONT watch video presentations etc.

Why is it that we have a "right" to security on an aircraft but not on a bus, train, public building, walking down the street, etc?

Those proverbial slashers aren't just relegated to aircraft.

If everyone has a "right" to be secure against attacks, then why shouldn't we ban wine bottles, laptops, electrical cords, metal eating knives, etc. The United States was not built on the premise of protecting everyone everywhere all the time. Under your premise, then neither knives nor handguns for which the owners have concealed permits should be permitted on the bus I ride.

Don't forget that the flight deck also has the options of doing a decompression and a sharp dive. An attacker can't make it too far nor too fast without the oxygen from the drop-down masks.

But what's the difference in pulling a knife versus using what's already at someone's disposal in the aircraft?

Metal knives have made their return on UA flights (as of 3/15/07). You can kill someone with a pen, you can walk right up to the galley and break the bottle of wine the FAs are using and certainly use that as well.

The point here is that if all of these weapons have been at someone's disposal for such a long time, why haven't they been used?

Oh, please! Please do not give them any ideas to start this on a bus, train, public building or walking on a street. There are enough idiots cranking out new rules and regulations that it is hard to know whether to laugh or cry.

Please show me where this is a "right" guaranteed by the Constitution - or elsewhere, for that matter.

An expectation is different from a "right".

Because we've seen them so often that we tune them out. Heck, my wife won't even let me get started on the FAA mandated briefing when we go fly. She knows how to fasten her seatbelt and open the door. And she isn't interested in taking the controls, so I could get away with "Get in, sit down, buckle up and hang on."

And it appears that the TSA doesn't either. As of 29 March, the video at EWR still talks about 3.0 oz.