I'm no expert on airport security. But I'm not surprised that the Transportation Security Administration didn't come out looking good in recent studies, as described in Orin's last post. I have had personal experience with their incompetence. Here are two examples.

In 2004, my brother was on an international flight originating in the US, and was trying to get something out of his carry-on luggage. To his surprise, he found a Swiss Army knife in there. He hadn't been trying to sneak the knife on the plane, but had simply forgotten to remove it from his backpack before packing for the trip. Yet the TSA missed it. Obviously, if you can sneak a knife through TSA security without even trying, imagine what a moderately competent terrorist who actually was trying might be able to get on board?

Then there was the time in 2002 when I was waiting in line to have my checked baggage X-rayed by TSA. For some reason, I struck up a conversation with one of the TSA agents there. To my surprise, he launched into a detailed description of exactly what kinds of things their equipment could detect and what kinds it couldn't. I interrupted him to ask whether he was really allowed to reveal this information. He assured me that he was, which leads to the conclusion that TSA either has very lax secrecy rules about its procedures, or hires a substantial number of very stupid agents, or perhaps both.

Now I readily grant that these two cases might be exceptional. I'm sure there are plenty of competent and dedicated TSA personnel. In fact, let's stipulate that 90% of TSA screeners are more competent than the individuals involved in these two cases were. Still, a failure rate this high has to be cause for concern. If hijackings succeed 10% of the time, the terrorists might well take those odds. And if only a minority of TSA agents are lax about revealing their capabilities, it is likely that the information will quickly get to the terrorists.

Moreover, as Orin suggests, the underlying problem may not be merely incompetence by individuals, but the generally poor performance incentives in government bureaucracies. TSA personnel, like most other government bureaucrats, are highly unlikely to be punished or fired for their mistakes. Numerous studies suggest that contracting out to private firms both reduces the price and increases the quality of goods and services relative to direct government provision. As this Reason Foundation study by airport security and privatization expert Robert Poole points out, private provision is the model used for airport security in Israel and Western Europe, where the system is generally better run than in this country. Certainly, I doubt that I could sneak a knife past Israeli screeners without even trying.

UPDATE: I am impressed by the number of commenters with similar stories of accidentally getting weapons through TSA screening, including weapons such as switchblades that are more formidable than a Swiss Army knife. It doesn't say much for the TSA's competence.