Just in time for the holiday rush, airline passengers will once again be subject to random secondary security searches, including "pat-downs," starting Dec. 22.

That means some folks will be pulled aside for another going-over after they already pass through a metal detector and their carry-on bags are inspected at airport security checkpoints. That going-over, too, is being revamped.

On the same day, the restrictions loosen for what passengers can carry on the airplanes. Back in: scissors with blades less than 4 inches and screwdrivers and other tools that are 7 inches or less.

The changes will enhance safety, security officials say, because they'll take the predictability out of searches and reduce the time security workers spend searching bags for small scissors so they can focus on more-dangerous items.

Some passengers are concerned it will all add up to much longer lines and confusion.

"Whether you were a frequent flier or a potential terrorist, you knew what to expect,'' said Kip Hawley, Transportation Security Administration assistant secretary. "With the changes we are implementing later this month, that predictability will be gone."

Screening procedures will be easy for passengers to navigate, he said, but difficult for terrorists to manipulate.

The TSA won't say what percentage of passengers will get the random checks. They now can face extra screening because of actions such as buying a one-way ticket with cash or refusing to remove shoes at checkpoints.