Earlier this year, I wrote about a somewhat confusing (albeit pleasant) experience I’d had at McCarran International Airport in Las Vegas, where I and a number of other travelers were put through the TSA’s expedited PreCheck line — meaning no removal of shoes, belts or jackets — in spite of not being enrolled in the PreCheck program. At the time, the TSA didn’t offer too much insight into why this had happened, but a new report sheds some more light on the topic.

Back in January, a TSA rep explained to me that I’d been the beneficiary of something called Managed Inclusion, which is intended to both speed up the screening process by making on-the-fly risk-based assessments that will let more people use the faster PreCheck lanes, while also shaking up that same process to make it less predictable.

According to BusinessWeek, what’s behind this unpredictability is an app called “randomizer,” which is currently being used at around 100 airports to funnel some travelers out of long lines and into the faster PreCheck lines, which move about twice as quickly as the others.

The randomizer is used during those peak times when lines usually become congested with travelers trying to make their flights. Since the PreCheck program requires a registration process and an $85 fee, many people haven’t enrolled. So rather than let the PreCheck line go unused — and since even the TSA acknowledges that terrorists are the extremely rare exception and not the norm — it uses the randomizer and other risk-based methods to move people through the PreCheck line even though they aren’t part of the program yet.

The TSA tells BusinessWeek that, as PreCheck enrollment grows, it will likely use the randomizer less frequently because the PreCheck lines will be busy with registered travelers.

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