With Thanksgiving kicking the end-of-year travel season into full gear, concerns over air travel safety have predictably resurfaced. The main issues this time surround the Transportation Security Administration's (TSA) advanced imaging technology (AIT) machines—even though the agency has been rolling out these devices over the past few years—as well as the TSA-administered security pat-downs of passengers who refuse to submit to AIT screening.

Controversy has bubbled up this month on a number of fronts. Some question whether AIT, which uses millimeter wave and backscatter imaging technology to detect metallic and nonmetallic objects and substances, poses a health risk. Other major concerns are that AIT images are the equivalent of a virtual strip search, that the TSA stores these images and that the machines tend to malfunction.

The TSA denies all of these allegations but recently softened its stance on its latest approach to aviation security. In a statement posted to the TSA's Web site on Sunday, agency administrator John Pistole noted that the TSA will work to make the procedures "as minimally invasive as possible" and that all security programs must undergo "a continual process of refinement and adjustment" as feedback is received from the public.

Yet Pistole also cited recent threats as the reason for the increased vigilance at airports. Earlier this month, a group known as Al-Qaeda in the Arabian Peninsula announced Operation Hemorrhage, a campaign to launch a series of smaller, low-cost attacks (the explosives on the cargo planes intercepted in Dubai and England cost $4,200 to make, the group says) against the U.S and its interests that disrupt commerce and perpetuate an "environment of security phobia." (pdf)

To address health concerns that have been raised about the new scanning equipment, the TSA has said that the backscatter radiation doses for the individuals being screened, operators and bystanders "were well below the dose limits specified by the American National Standards Institute (ANSI)." The agency also says that the energy projected by millimeter wave technology is "thousands of times less than a cell phone transmission." The TSA expects to deploy a total of 450 AIT units at airports across the U.S. by the end of this year.

Reactions to the pat-downs have added increased scrutiny of the TSA's approach to tightening security. Some say the TSA has crossed a personal privacy boundary by authorizing pat-downs for any passengers who set off metal-detector alarms or opt out of using the AIT. High-profile protests have been initiated, including one by 15-minute YouTube hero John Tyner, who refused both to use the AIT and to submit to a pat-down on November 13. And Rep. John Mica, R-Fla., is calling for a review of the TSA's pat-down procedures as well as the replacement of TSA workers with private contractors.

Far less visible are suggestions for practical alternatives to the TSA's security policies. Scientific American asked Brian Michael Jenkins, a senior advisor at the RAND Corp. and a former member of the White House Commission on Aviation Safety and Security, for his perspective on the TSA's latest moves and other options for tightening aviation security.

[An edited transcript of the interview follows.]

The TSA has been testing Advanced Imaging Technology (AIT) machines for years. Why has this become such a high-profile issue over the past few weeks?
Though they've been studying this for years, it was only after the December [25, 2009] attempted bombing of the flight over Detroit by Umar Farouk Abdulmutallab that led to the decision to deploy thousands of them across the United States. The time of year also has something to do with the attention this is getting. We're going into the Thanksgiving and Christmas holidays, which are peak travel times when people who do not otherwise travel find themselves at airports and on airplanes. So you have larger passenger loads, and you tend to have longer lines at security check-points. You also have the news media's seasonal coverage of commercial aviation issues this time of year. This year, these travel stories have elements that are particularly attractive to our contemporary news media: First, it's a story about terrorism and, number two, if you read between the lines in these stories, particularly on television, you're talking about groping, modesty, nakedness and the genital area. This combines terrorism with titillation and leads to precisely the kind of lurid coverage that has come to characterize the American news media.

There's no question that the body scanners and the physical pat-downs taking place now are more intrusive, and that is provoking a reaction. The problem over the long term is that terrorists can build and conceal devices on persons in places that will make them undetectable to all but the most intrusive searches. So, it's a more intrusive measure in response to an evolution of terrorist tactics; it is a bit of fabricated theater because the vast majority of the passengers accept the measures, and it is a bit of agenda-serving by passengers' rights groups and posturing politicians that neatly come together.

Is backscatter AIT "nothing more than an electronic strip search," as it has been called by the American Civil Liberties Union (ACLU)?
Put aside the ACLU statement, because I cannot recall in the last 15 years a single security measure at airports that they haven't opposed on grounds of the Fourth Amendment. So that's a hearty perennial. I don't mean to put them down. I honestly do believe that we do have to debate these security issues in our society as a society and decide what impositions we accept in return for what risks we are willing to take. That's a good debate, and it's a tough one.

I'm not a techie, but I have my reservations about the technology. I think that the decision to deploy the body scanners was driven primarily by a need to be seen doing something after the Abdulmutallab attempt. These machines are calibrated, and depending on the degree of calibration it is not certain in my mind that the device would have detected Abdulmutallab's bomb had he walked through a body scanner, given the quantity of the explosives he was carrying and where they were concealed. The likelihood of not detecting such a threat increases when you put measures in place to, understandably, protect personal privacy and modesty by blurring certain areas of the body, including the genitals, where Abdulmutallab was carrying the explosives.

If the TSA's latest technology does not greatly improve security, why are these machines being installed in so many airports?
The deployment of the body scanners represents a symptom of a longer term problem that we have to face. Passenger loads are increasing and so are the number of security procedures, in each case following a particular event. Following Richard Reid, the shoe bomber in 2001, we now take off our shoes. Following the Heathrow plot in 2006 [to carry explosives on board planes going to the U.S. and Canada] we now have restrictions on liquids. Following Abdulmutallab in 2009 we now have body scanners. But continually adding measures to look for objects over the long term may not be sustainable without completely degrading the screening performance. My objection to the body scanners is it was a missed opportunity. It was throwing another machine out into the airports without seizing the moment to do a fundamental review.

What improvements or alternatives are there to the current approach to air travel security?
We really need to fundamentally rethink the strategy of how we do this, and it's not an accumulation of yet another procedure or another piece of machinery. We really have to think about the issue of whether we focus our security efforts 100 percent on looking for objects or whether move toward a more discerning system that also begins to look at categories of travelers.

We board about one billion passengers in the United States per year, but that's not one billion different people. Frequent fliers account for the vast portion of total boardings. Moving some of them into a registered traveler category, where they willingly submit personal information as part of a pre-screening process, would free resources to be applied to other passengers. [The TSA concluded its two-year Registered Traveler test program at 19 airports in July 2008 but decided not to implement the program. Instead, the TSA has encouraged private sector vendors including Vigilant Solutions and FLO Corp. to provide pre-registration service in conjunction with airports and airlines. The TSA does have a prescreening program called Secure Flight that attempts to match passenger records with records of people on terrorist watch lists at the time domestic airplane tickets are purchased. Prior to Secure Flight, airlines conducted passenger watch list checking.]

You've said that security can be improved by randomly applying better detection measures. How might this work?
We know that terrorists watch our systems. When a system becomes routine and predictable, they will identify the vulnerability and go after it. The shoe bomber is an example and Abdulmutallab is another. There should be an element of randomness in which some passengers would be subjected to the more rigorous search methods based on the passenger's records and documentation and on behavioral assessments that security professionals make. Observations of people's behavior are just as important as the search procedure itself.

On top of that, you could have a computerized system that selects passengers at random for higher-level screening. This would not be an interrogation or an interview, and it would also apply to frequent travelers. We know that this type of randomness really is an impediment to terrorist planning, but it's also important from the standpoint of civil liberties because passengers are not singled out for any particular reason.

What are the chances that we'll see such an approach at airports in the near future?
There's a certain amount of receptivity to it, certainly on the part of the security screeners. Where it runs into barriers has more to do with public attitude and, to put it bluntly, posturing politicians. Americans prefer their security to be passive, nonintrusive and egalitarian. People feel more comfortable when exactly the same procedures are applied to every single person, which is of course the dumbest way we can do it. The minute you try to segregate people, it immediately raises allegations that this is somehow based on ethnic or racial profiling or there are other nefarious criteria that are being used to make these decisions.

With regard to the attitudes of politicians, sometimes people in Washington pretend that what we have at airports around the country is 100 percent prevention. The fact is there is no such thing as 100 percent prevention.

How much progress has been made with regard to air travel security since 9/11?
If you take the long view on this, security has had an effect on the number of hijacking attempts and airline sabotage attempts. There is no question that, as a consequence of screening measures and other factors, the number of attempts by terrorists has significantly declined over the years. In the 1970s and 1980s we were looking at a terrorist hijacking or an attempted terrorist sabotage of an aircraft something close to once a month. If you look at the post-9/11 environment, clearly there have been plots and failed attempts, but we're looking at one of these incidents per year. We have obliged our adversaries to make smaller devices and use exotic substances to try to conceal them, and that renders them far less reliable. Yes, Richard Reid made it onto a plane with his shoe bomb, and Abdulmutallab made it on with his underpants bomb, but the bombs didn't work. So we've decreased the number of attempts and increased their operational difficulty. That is a positive result, but we're running into this dilemma now as the devices get smaller and concealment gets better—the terrorists will work this out. The challenge is how do we deal with that in our society in a way that is acceptable to society?