Analysts said last week it was unclear whether the TSA's decision to send fewer nonenrolled travelers through PreCheck screening lines beginning early this month represents a change in direction brought about by the Trump administration or the continuation of a progression that began under the Obama presidency.

"It's really hard to tell," said University of Illinois computer science professor and aviation security expert Sheldon Jacobson, citing the relative secrecy with which the TSA designates nonenrolled fliers to use PreCheck.

Under PreCheck, which now has more than 4 million enrolled members, the TSA performs background checks on applicants, and those who are approved pay $85 for five years. In addition to enjoying the use of separate, often faster lanes at many airports for the identity-check portion of the screening process, PreCheck members can pass through security stations without taking off shoes and belts and without removing laptops from their carry-ons.

At present, fliers who aren't PreCheck members are also sometimes allowed into PreCheck lines, selected through a risk calculation based on information they provided to airlines during the ticketing process.

The TSA moved toward that method after abandoning a policy called "managed inclusion" in September 2015, under which agents on the scene selected non-PreCheck travelers to use the PreCheck lane.

In a statement last week, the TSA called the latest move to make the PreCheck lanes more exclusive a natural progression.

"In the future, we intend to only have enrolled or pre-vetted passengers, or those screened by canines, in the expedited screening lanes," the TSA said.

Citing security concerns, the agency did not provide details about how many nonenrolled fliers have until now been selected for PreCheck clearance, nor did it say how much the reduction would be.

Bruce Schneier, a fellow at Harvard's Kennedy School of Government who specialized in security, said that since the agency doesn't provide those numbers, it will be impossible to know if and to what extent such a reduction even takes place in the coming month and beyond.

But Schneier, a sharp critic of PreCheck, also said it did not matter. The enhanced airport screening measures implemented after 9/11, he said, are useless "security theater. … Intelligence, investigation and emergency response — that's what works."

Jacobson, who supports PreCheck, said the move to allow fewer nonmember travelers to use PreCheck lanes is a prudent step. Granting trusted traveler status to fliers who haven't gone through a background check raises questions, he said.

"If vetting done by the airlines is sufficient for security, then why do we need background checks in the first place?" Jacobson said. "On the other hand, if it's not adequate, then what we're doing is creating a security vulnerability."

The move to tighten access to the PreCheck lines comes approximately eight months after security-check lines that frequently lasted longer than an hour in large airports thrust the TSA onto network news programs and across the front pages of newspapers. The crisis was resolved quickly after Congress freed up $62 million of TSA funds that had been designated for other expenditures and after airports and airlines also used their own funds to increase staffing that facilitated the work of the actual TSA screeners.

In addition, communication between the TSA, airlines and airports was improved with the establishment of an incident command center, which coordinates daily calls between the parties.

The TSA said it doesn't expect that the decision to reduce the number of nonenrollees who can pass through PreCheck lanes will affect lines because the measures put in last year are still in place.

"That said, the TSA will monitor operational impacts of these changes on airport checkpoints and on TSA PreCheck enrollment capabilities and adjust resources accordingly," the agency said.

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