It is late at night and I got a little agitated reading some of the comments at Schneier's blog post about airplane security. When I'm tired my inhibtions drop and I write things I might not normally. Here's a duplicate of the rant I left in Schneier's comments:
Regarding dust explosions...
This is about 8 ounces of flour over an ounce of black powder (the original gun powder): http://www.joehuffman.org/FlashTek/06-FFFFgFlour.mpeg
That is in open air. In an enclosed room of an abandoned house a similar test brought the house down. Sorry, that wasn't my test and I don't have any video for it.
Shaped charges made from match heads? I don't think so. The "detonation" velocity is just too slow. It's more properly called deflagration than detonation for that type of "explosive". Shaped charges require MUCH faster propagation rates.
Binary explosives are available here: http://www.tannerite.com/ No background check, no license required, delivered to your door via UPS. Now THAT is something you can make a crude shaped charge with.
The "projectile" (typically a slug of molten copper) from a shaped charge is moving at 6 to 10 kilometers per second. At the pressures generated when it hits a "target" everything is "plastic". Hardened steel develops a hole just like a high velocity stream from your garden hose nozzle punches a hole in a dirt bank. Penetration for a properly configured 10 (ten) gram shaped charges is about 2 inches of steel. Yes--a shaped charge using less than one half ounce of explosives will penetrate two inches of steel. See Explosives Engineering by Paul W. Cooper, ISBN 0-471-18636-8 page 442. Or do you think the doors to the cockpit are more resistant than two inches of steel?
Do you think someone could not get a half ounce of explosives through TSA security? You could probably successfully hide that in your mouth or arm pit if you didn't want to use some other body cavity.
Oh, and you know why the explosives detectors work fairly well with plastic explosives? It's, by international agreement (Montreal, March 1, 1991, Article XIII of the Convention on the Marking of Plastic Explosives -- http://www.atf.gov/explarson/fedexplolaw/subpartj.pdf ), that all plastic explosives be "marked" by their manufacture with a chemical that is easily detected. Do you think Iran and others are going to abide by that International Convention if they want to provide some terrorists plastic explosives?
We really should spend the $2 billion/year, or whatever it is, on finding and stopping the bad guys before they arrive at the airport/train-station/shopping-mall/etc. than on pointless screening. The bottom line is that the acronym TSA should be reversed--it really stands for "A Security Theater".