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Late last month, the Transportation Security Administration found a live explosive device in a checked bag month at Lehigh Valley International Airport in Pennsylvania. TSA officers took the appropriate actions and confirmed the find. Airport surveillance camera footage helped authorities identify a suspect, and the FBI made an arrest.

There are lessons to be learned from this incident.

As much as the TSA touts stopping firearms from getting onto airplanes, explosives are a more dangerous threat to the air system. That is why travelers are limited to 3-ounce liquids, aerosols, gels, creams and pastes in their carry-on bags.

With improvised explosive devices, numerous factors can mask what the item is and make it easy to miss. In the Pennsylvania case, the explosive appeared somewhat simple, making it possible to detect. TSA screeners were on target with their attention.

Of critical importance, the person now in custody was known to local law enforcement. Such individuals should be given extra security screening — of their person, carry-on bags and checked luggage. This is the foundation of risk-based security, which aligns security resources with security risk.

If a person is known to local law enforcement, this should flag them for additional attention at airports. Fortunately, most people do not carry such a record. However, the few who do demand extra screening. In this case, the person's checked bags needed extra attention, and fortunately, such attention prevented the likelihood of an air system incident.

So how can the TSA effectively concentrate its attention on the right people?

The TSA PreCheck program is designed for this purpose. When people subject themselves to the requisite background check, they become a known traveler to the TSA. And known travelers pose significantly lower risk to the air system.

This means that offering PreCheck at no cost to anyone willing to undergo the background check should be a top priority for the TSA. The expense of offering PreCheck for free would be recouped by the cost savings at airport security checkpoints in personnel and security equipment.

Anytime the TSA uses security resources and places excessive attention on a TSA PreCheck-vetted passenger, the agency is making two mistakes that effectively make the air system riskier.

First, the security resources and attention are being squandered, as the benefits accrued from such security are dwarfed by the costs.

Second, attention placed on vetted passengers is not being used on nonvetted passengers.

Most people believe that the TSA has access to an unlimited amount of security resources to protect the air system. Overallocating security resources to PreCheck passengers appears benign. But choices must be made on how to use security resources. When security resources are inefficiently directed, the security of the air system is marginally compromised.

Technology can support and enhance human judgment, but it can never replace it. And the best way to optimize the judgment of people is to minimize distractions that can lead to human error.

The good news is most passengers pose little risk to the air system. Yet finding the few who do is akin to finding needles in a haystack. The best approach that the TSA can take is parsing the haystack so that known travelers are partitioned away from unknown risks. Then the TSA can use its limited resources to focus on these risks.

As authorities learn more about the suspect in the Pennsylvania case, the hope is that this person acted as a lone wolf. This information will reaffirm TSA's mission and the benefits of risk-based security. Any other approach to security is not only wasteful, but it also makes the entire air system less secure for all.

Sheldon Jacobson is a professor of computer science at the University of Illinois at Urbana-Champaign. He applies his expertise in data-driven risk-based decisionmaking to evaluate and inform public policy. He has studied aviation security for more than 25 years, providing the technical foundations for risk-based security and TSA PreCheck. This article was first published by the Chicago Tribune.