The LA Times reports that

Los Angeles International Airport screeners failed to spot simulated bombs in 75% of tests last year

(I was passed the link courtesy of Ben Goldacre's blog). The testing made clear the possibilities for carrying out a 'successful' attack using publicly available material and components:

Using cheap, easily available components, GAO investigators made an explosive device and a firebomb that, when tested, exploded with sufficient force to cause significant damage. Investigators then used public information on the Transportation Security Administration's screening procedures to devise ways to carry the bomb components through airport checkpoints without being challenged.

This poor performance was despite an "e-mail from TSA headquarters that not only warned employees of testing, but described the methods and appearance of those conducting the probes".

This is all somewhat disappointing - and serves as a reminder that, however 'advanced' the technological fix, there's always scope for a range of factors to mess things up. I would see this type of incident as a reason to both reconsider how airport security is handled, and to look at the broader social and political factors around the 'terrorist' threat. How the TSA and US government views it remains to be seen...